O CRGANIARDENING GExtension Bulletin 0648

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Organic Gardening ................................. 1

Overview of Soil Management .............. 1

Adding Organic Matter ..................... 1

Composts ........................................ 2

Making Compost .......................... 2

Using Compost ............................. 2

Green Manure ................................. 2

Mulches........................................... 3

Weed Control ................................ 3

Soil Moisture and Temperature .... 4

Tilling Mulches into the Soil ......... 4

Nutrients and Fertilizers .................. 4

Comparing Organic and

Synthetic Fertilizers ......................... 4

Slow Release of Nutrients................. 5

Types of Organic Fertilizers .............. 5

Animal Manure ............................ 5

Biosolids ...................................... 7

Commercial Organic Fertilizers..... 7

Lime, Gypsum, and

Wood Ashes .................................. 8

Establishing How Much Organic

Fertilizer to Use ............................... 8

Soil Tests ..................................... 9

Extension Bulletins ...................... 9

Tips for Estimating Organic

Fertilizer Rates ............................. 9

Plant Disease Control ........................... 10

Plant Disease Principles .................... 10

Methods of Combating

Plant Diseases .................................. 11

Exclusion ...................................... 11

Eradication .................................... 11

Protection ...................................... 13

Genetic Resistance ........................ 15

Small Fruit Disease Resistance ...... 15

Black Raspberries ...................... 16

Insect Management .............................. 16

Biological Control of Insect

and Mite Pests .................................. 16

Lady Beetles .................................. 17

Predator Mites ............................... 17

Predacious Ground Beetles ............ 17

Green Lacewing ............................. 18

Syrphid Flies, Flowerflies ............... 18

Aphid Parasites ............................. 18

Fungi ............................................. 18

Nematodes..................................... 18

Other Beneficials ........................... 19

Insect Disease Organisms .............. 19

Birds ............................................. 19

Cultural and Mechanical Control of

Insect and Mite Pests ........................ 20

Natural Insecticides ....................... 24

Pyrethrins ..................................... 24

Neem ............................................. 24

Dormant and Summer Oils ............ 24

Lime-Sulfur ................................... 25

Elemental Sulfur ........................... 25

Soaps ............................................ 25

Certified Organic Produce ................. 25

Selected References ........................... 26

Table of Contents

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1

Overview of SoilManagement

A good garden soil allows water to enter,and excess water to drain from the root zone.It has the capacity to hold water, air, andnutrients available for plants and microor-ganisms. It has a stable structure that is easyto dig and resists erosion.

Improving and maintaining a garden soilinvolves:

• Proper use of soil amendments toprovide organic matter and plantnutrients

• Tillage at appropriate times• Prevention of runoff and erosion

Adding Organic MatterOrganic matter builds and stabilizes soil

structure, improving the porosity, infiltration,and drainage of the soil, and reducing ero-sion. It holds water and nutrients for plants.Organic matter also is a long-term, slow-re-lease storehouse of nitrogen, phosphorus,and sulfur. Soil microorganisms continuallybreak down organic matter. Gardeners usecomposts, plant residues, and mulches toreplenish soil organic matter. These materi-als are relatively low in available nutrients,and can be added to the soil in largeamounts.

Organic GardeningAuthors

Art Antonelli, Ph.D., Washington State University Extension entomologist, WSU Puyallup;Craig Cogger, Ph.D., WSU Extension soil scientist, WSU Puyallup;Holly Kennell, M.S., WSU Extension area agent, Snohomish County;Carrie Foss, M.S., WSU Extension pesticide education associate, WSU Puyallup;Roy Van Denburgh, Ph.D., WSU Extension agent, emeritus, Yakima County; andVan Bobbitt, M.S., Horticulturist, South Seattle Community College.

Organic gardening relies on ecologicalprinciples and natural processes to grow andmanage garden crops. Although organic gar-deners avoid the use of synthetic pesticidesand fertilizers, organic gardening is not a listof substitutes for synthetic products or a setof home remedies to kill pests. Organic gar-dening is a holistic approach that involvesunderstanding soil management, integratedpest management, and the life cycles ofplants, pests, and the pests’ natural enemies.When properly done, organic gardening canproduce high quality food and landscapes,enhance the garden environment, protectwater quality, and conserve natural resources.

The basic soil management and pest man-agement approaches of organic gardeningmake sense for all gardeners, whether youavoid all synthetic fertilizers and pesticidesor not. Using these approaches will reducethe amount of fertilizers and pesticides youneed, and can improve the quality of yourgarden.

Other benefits of organic gardening in-clude increasing the number and diversityof beneficial organisms and turning wastematerials into valuable composts and fertil-izers for the garden.

Organic gardening means actively work-ing with nature in your garden. Organic gar-deners need to be smart gardeners—know-ing the garden environment, observing plantsand pests, knowing choices for management,and acting at the appropriate times.

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CompostsComposts provide an excellent source of

organic matter for garden soils. Compostingalso closes the recycling loop by turningwaste materials into a soil amendment. Youcan make compost at home or buy commer-cially prepared compost, often made fromyard or food waste.

Making CompostThe key to composting is to supply a bal-

ance of air, water, energy materials (grassclippings, green garden trimmings, or freshmanure), and bulking agent (corn stalks,straw, and woody materials). You don’t needto buy additives to stimulate your compostpile. You just need to provide conditionsfavorable for natural composting organisms.

Home composting can be done in hot orcold piles, in worm bins, or in soil trenches.

• Hot (or fast) composting produces ahigh-quality, finished compost in 6 to 8weeks. To maintain a hot compost pile,balance and mix energy materials andbulking agents, keep the pile moist, andturn the pile frequently to keep itaerated.

• Cold (or slow) composting requires lesswork than hot composting. Build thepile, and leave it for months or longerto decompose. Cold composting doesnot kill weed seeds. Some gardenershave problems with rats and other pestsattracted to edible wastes in compostpiles.

• You can compost fruit and vegetablescraps in a worm bin. This is a goodmethod for urban gardeners who havesmall amounts of space.

• You also can bury fruit and vegetablescraps and allow them to decomposedirectly in the soil.

The WSU Cooperative Extension bulletin,Backyard Composting, EB1784, gives moredetailed information on making and usinghome compost.

Using CompostYou can till or dig composts directly into

the garden, or use them as a mulch over thewinter or summer before turning them intothe soil. One cubic yard of compost coversabout 300 square feet of garden one inchdeep. Adding 1 to 2 inches of compost eachyear helps build a productive garden soil.

In the first year after application, com-posts that are woody and not fully decom-posed will tie up part of the soil nitrogen,resulting in nitrogen deficiency for the plants.If plants show signs of nitrogen deficiency,add extra nitrogen (manure, blood meal, cot-tonseed meal, biosolids). In following years,most composts will contribute small amountsof available nitrogen to the soil.

Green ManureGreen manures are cover crops grown spe-

cifically to be tilled or dug into the soil. Plant-ing green manure is a way to grow your ownorganic matter. The value of cover crops goesbeyond their contribution of organic matter.Cover crops also can do the following:

• Capture and recycle nutrients thatotherwise would be lost by leachingduring the winter

• Protect the soil surface from rainfallimpact during the winter

• Reduce runoff and erosion• Help suppress weeds• Supply nitrogen (if legumes are grown)

No one cover crop provides all of these ben-efits. Deciding which cover crop or crop com-bination to grow depends on which benefitsare most important to you, and which covercrops fit best into your garden plan. You cangrow cover crops over the winter or in sum-mer.

Gardeners usually plant cover crops in thefall and till them as green manure in thespring before planting. The earlier cover cropsare planted, the more benefits they will pro-vide. Research in western Washingtonshowed that cereal rye planted in Septem-

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ber captured three times the amount of ni-trogen as an October planting. Legumes,such as vetch and crimson clover, need anearly start to cover the soil before coldweather arrives.

Because gardeners often grow crops intoNovember or December, it is not possible toplant early cover crops throughout the gar-den. In this case, plant cover crops in areasthat you harvest early, and use mulches onparts of the garden you harvest later. Forexample, plant a cover crop in a sweet cornbed immediately following harvest in Septem-ber. You also can start cover crops aroundand among late crops where space allows.

Table 1. Examples of cover crops grownin Washington

Cereal Rye Very hardy, grows quickly,matures rapidly in spring

Winter Wheat Leafy, covers soil well,matures slowly

Hairy Vetch Legume, fixes nitrogen,starts slowly, grows quicklyin spring, good companioncrop for cereal rye

Crimson Clover Legume, fixes nitrogen,slower growth than vetch

Buckwheat Fast growing, frost-sensi-tive, summer cover, ready totill in 30 days

Till or dig cover crops into the soil beforethey flower. After flowering, the plants be-come woody and decline in quality. Also, dig-ging the crop into the soil becomes quite dif-ficult if the plants grow too large. If you can-not till a cover crop in time, cut it off andcompost it for later addition to the soil. Youwill still get the short-term benefit of organicmatter from the crown and roots when youtill your garden.

The fresh organic matter from cover cropsstimulates biological activity in the soil andimproves soil structure. A good stand of vetchor clover can supply about half of the nitro-gen needed by the next garden crop. Becausecover crop residues decompose quickly in thesoil, these benefits last only about a year.Make cover crops an annual part of yourgarden rotation to gain their benefits eachyear. If cover crops do not fit into your gar-dening plan, use winter mulches as a sub-stitute. WSU Extension Bulletin EB 1824,Cover Crops for Home Gardens in WesternWashington and Oregon, gives details onchoosing and managing cover crops. Formore detail on individual cover crops referto EM 8704, Using Cover Crops in Oregon,available from the Oregon State UniversityExtension Service.

MulchesDuring the summer, mulches control

weeds and conserve moisture. Wintermulches also protect the soil from raindropimpact and runoff. Organic mulches mixedinto the soil at the end of the season will de-compose and add to the soil organic matter.

Mulches are categorized into two groups:

1.Organic mulches include materialssuch as straw, leaves, compost, grassclippings, and sawdust. Till thesematerials into the soil at the end of theseason or leave them on the surface.Use bark mulches or wood chips aroundperennial plantings and on paths. Donot till them into the soil.

2.Synthetic mulches include blackplastic and weed-blocking geotextiles.Remove and discard these materialswhen they are no longer useful asmulches. Some people use old newspa-pers or cardboard as a synthetic mulchthat will decompose in the soil. Covernewspapers and cardboard with organicmulches to improve the appearance ofthe garden.

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These two types of mulches provide some-what different benefits, described below.Many organic gardeners avoid plasticmulches because they cannot mix them intothe soil or recycle them.

Weed ControlMulches control weeds by blocking light.

Black plastic, geotextile, and cardboardmulches also provide a physical barrier toweed growth. Mulches alone will not controlweeds, but they can be a key part of gardenweed management. Mulches have limitedeffectiveness against perennial weeds suchas horsetail, quackgrass, and morninglorythat can send rhizomes or roots consider-able distances.

To control weeds, remove weed seedlingsfrom the area and apply 1 to 2 inches of or-ganic mulches when desirable plants are 2to 3 inches tall. Be careful not to cover theplants themselves. You may need as muchas 6 inches of straw mulch. Although weedseeds can germinate in a mulch, it is easierto pull young weeds from mulch than fromsoil.

Soil Moisture and TemperatureOrganic mulches help maintain soil mois-

ture by improving movement of water intothe soil, and by reducing evaporation fromthe soil surface. Plastic mulches reduce bothevaporation and infiltration. We do not rec-ommend plastic mulches in perennialplantings because the mulches make watermanagement more difficult. Soils remain wetlater in the spring beneath plastic mulches,creating soil conditions that encourage rootrots. In the summer, plastic mulches reducethe effectiveness of overhead irrigation.

Mulches can either increase or decreasesoil temperature, depending on the type ofmulch. Loose organic mulches insulate thesoil. This is a disadvantage in the springwhen warm soil temperatures are needed tospeed germination and growth. In the heatof summer, organic mulches can be a ben-

efit, keeping soils cooler. Black plastic ab-sorbs heat, and warms the soil in the spring,creating a better environment for warm sea-son crops like melons.

Tilling Mulches into the SoilYou can turn organic mulches into the

soil in the fall or spring, depending on yourgarden plan. Digging or tilling mulches isusually easier than tilling cover crops. Somemulches—sawdust and straw—contain littlenitrogen. Once turned into the soil, they willtie up a large amount of nitrogen. To pre-vent nitrogen deficiency in the next crop,add fertilizer—blood meal, cottonseed meal,or manure.

Nutrients and FertilizersSoil is the source of most plant nutrients.

Carbon, hydrogen, and oxygen come from airand water. The soil supplies the remaining13 essential nutrients. We add fertilizers tosupplement native soil nutrients. This pro-motes plant growth and replaces nutrientsremoved when plants are harvested.

Comparing Organic andSynthetic Fertilizers

Organic fertilizers are natural materialsthat have had little or no processing. Theyinclude both biological (plant and animal)and mineral materials (Table 2). Organic fer-tilizers release nutrients through natural pro-cesses in the soil, including chemical weath-ering of mineral materials, and biologicalbreakdown of organic matter. The releasednutrients are available to plants in a water-soluble form. These soluble forms of nutri-ents are the same as those supplied by syn-thetic fertilizers.

When compared with synthetic fertilizers,organic fertilizers usually are less concen-trated in nutrients, and release nutrientsmore slowly. Larger amounts of organic fer-tilizers are needed, but their effects last

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longer. Organic fertilizers contain a varietyof nutrients, but the amounts are not alwaysbalanced according to plant needs.

Using organic fertilizers recycles materi-als that otherwise would be discarded aswastes. Production of synthetic fertilizers, onthe other hand, can create wastes and usesubstantial amounts of energy.

Slow Release of NutrientsOrganic fertilizers slowly release nutrients

to plants over the course of the growing sea-son. The rate of release of nutrients from or-ganic materials depends on soil microorgan-ism activity, which in turn depends on soiltemperature and moisture. Temperature andmoisture conditions that favor plant growthalso favor the release of nutrients from or-ganic matter.

Nutrients in most synthetic fertilizers areavailable immediately. They can furnish nu-trients to plants in the spring before the soilis warm. However, nitrogen in these fertiliz-ers is vulnerable to leaching loss from heavyrainfall or irrigation. Note: Once nitrogenmoves below the root zone, plants can nolonger use it, and it may leach into ground-water.

Some organic fertilizers contain imme-diately available and slow-release nutrients,nourishing plants both early in the seasonand later. Fresh manure, biosolids, and fishemulsions are examples of organic fertiliz-ers containing available nutrients. As ma-nure ages, the most readily available frac-tion is lost into the air or leached into thesoil, leaving slow-release material in the agedmanure.

Some material in organic fertilizers breaksdown so slowly that it does not become avail-able the first season after application. Re-peated application of organic fertilizers buildsa pool of material that releases nutrients veryslowly. In the long run, the pool will decreasethe need for supplemental fertilizer.

Types of Organic FertilizersAnimal Manure

Animal manures vary widely in nutrientcontent and nutrient availability, dependingon the type of animal that produced themanure, and the age and handling of themanure. Mixing with bedding dilutes ma-nure. Exposure to rain leaches nutrients.Composting under cover retains more nutri-ents, but reduces nutrient availability.

Table 2. Comparing organic and synthetic fertilizers

Organic fertilizers Synthetic fertilizers

Source Natural materials; little or noprocessing

Manufactured or extracted fromnatural materials, often undergoingextensive processing

Examples Manure, cottonseed meal, rockphosphate, fish by-products,ground limestone

Diammonium phosphate, syntheticurea, potassium chloride

NutrientAvailability

Usually slow-release; nutrients arereleased by biological and chemi-cal processes in soil

Nutrients usually are immediatelyavailable to plants

Usually high concentrationNutrientConcentration

Usually low concentration

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Table 3 compares typical nutrient val-ues of different manures. The nutrient con-tent of manure could differ substantially fromthe amounts in this table, depending on howthe manure was stored and handled.

Applying farmyard manures. It doesn’ttake much of a nutrient-rich manure, suchas poultry manure, to fertilize a garden. A 5-gallon bucket of poultry manure containsenough nutrients to fertilize 100 to 150square feet of garden. If more is applied, yourisk over-fertilizing, harming crops, andleaching nitrogen into groundwater.

Dilute manures, such as separated dairysolids and horse manure with bedding, con-tain far fewer available nutrients and can beapplied in larger amounts. You can use asmuch as an inch of these materials in thegarden every year. Use these manures mainlyas a source of organic matter.

Experiment with the amount you applyand observe the performance of your cropsto fine-tune your application rate. It is bet-ter to be conservative and add more manureif the crops appear deficient.

Commercial manure composts.Composted chicken and steer manures withknown nutrient contents are commerciallyavailable as bagged products. Table 4 showstypical analyses of these materials. Nutrientlevels and availability in steer manure com-post are so low that you should use steercompost as a source of organic matter only.Recommended application rates on packagesof these products are good guidelines for theiruse.

Table 4. Nutrient content of commercialmanure composts

Animal N P2O5 K2O

%

Chicken 1-3 0.5 1-2Steer 0.5 1-2 0.5

Using manure safely. Fresh manuresometimes contains pathogens that can causediseases in humans. These pathogens are nottaken up into plant tissue, but they can ad-here to soil on plant roots, or on the leaves orfruit of low-growing crops. Cooking destroyspathogens, but raw food carries a risk ofpathogen exposure. Washing and peeling rawproduce removes most pathogens, but somemay remain. The risk from pathogens is great-est for root crops (e.g. carrots and radishes)or leaf crops (e.g. lettuce or spinach), wherethe edible part touches the soil. The risk isnegligible for crops such as sweet corn, whichdo not come in contact with the soil, or forany crop that is thoroughly cooked.

Consider raw manure to be a potentialsource of pathogens, and avoid using freshmanure where you grow high-risk crops. Bac-terial pathogens die off naturally duringcomposting, extended storage, or after fieldapplication. Complete die-off of bacterialpathogens occurs in days to months depend-ing on the pathogen and environmental con-ditions.

Keep dog, cat, and pig manure out of yourhome compost and garden. Some of the para-

Table 3. Typical nutrient content ofuncomposted animal manures at thetime of application.1

Type N P2O52 K2O

Broiler with litter 33 29 30Laying hen 26 40 33Sheep 13 6 24Rabbit 11 7 10Beef 8 4 12Dry stack dairy 6 3 13Separated dairy solids 3 1 2Horse 6 4 111Divide these numbers by 40 to estimate the nutrients in a5-gallon bucket of fresh manure.2Phosphorus and potassium in this table are shown in unitsof P2O5 and K2O. These are the units typically used on fertil-izer labels. To convert from P to P2O5, multiply P by 2.3. Toconvert from K to K2O, multiply K by 1.2.3As-is is typical for manure stored under cover.

lb per cu yard as-is3

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sites found in these manures are very per-sistent, and may survive in both compost andsoil.

The best time to apply manure is in thespring before planting. You also can applymanure in the fall, but some of the nutrientsmay be lost over the winter. Environmentalrisks of leaching and runoff also increase. Ifyou do apply manure in the fall, apply it early,and plant a cover crop to help capture nutri-ents and prevent runoff.

Don’t overapply fresh manure. Becausefresh manure contains available nutrients aswell as slow-release nutrients, overapplica-tion can harm your crops.

A safe way to use fresh manure is to mixit into your compost pile and then use thefinished compost in your garden. The micro-organisms breaking down the other materi-als in your compost will absorb the availablenutrients, reducing the risk of nutrient over-application and leaching.

Because it is hard to maintain the hightemperatures needed to kill pathogensquickly in a backyard compost pile, allowyour manure compost to age for six monthsor more before using it in your garden. Analternative is to buy commercially compostedmanure.

BiosolidsBiosolids are a by-product of municipal

wastewater treatment. Federal standards fororganic farming do not include biosolids asan organic fertilizer. However, biosolids dohave two important characteristics of organicfertilizers: 1) their nutrients are released slowlyfrom the organic form by natural processesin the soil, and 2) they are a product of thewaste stream that can benefit crop growth.

Most of the biosolids produced in Wash-ington are used to fertilize agricultural andforest crops. The material used on farms isrich in nutrients and acts similarly to poul-try manure.

Some communities in Washington pro-duce a special class of biosolids and marketthem to gardeners. These are called Class A

biosolids: they have been treated using heator composting to reduce pathogens to back-ground levels, making them safe for all gar-den uses. Three types of Class A biosolidsare available in Washington: composts,blends, and heat-dried pellets. Biosolids com-posts are made from biosolids and yard de-bris or woody materials, and can be usedsimilarly to other composts. Biosolids blendsare formulated for different uses, includingturf topdressing, mulches, and soil amend-ments. Heat-dried pellets are rich in nutri-ents and are used similarly to commercialorganic fertilizers. Check with your localwastewater treatment plant to see if they haveClass A biosolids available for home use.

Commercial Organic FertilizersMany organic by-products and some un-

processed minerals are sold as commercialorganic fertilizers. Table 5 shows approxi-mate nutrient content of some of thesematerials. Figures represent total nutrientcontents; because most are slow-release fer-tilizers, not all of the nutrients will be avail-able the same year they are applied. The tableshows that each fertilizer contains one mainnutrient. The other nutrients are present insmaller amounts. Several companies producebalanced organic fertilizers, blended into asingle product that provides all of the pri-mary nutrients.

Commercial organic fertilizers tend to bemore expensive per pound of nutrients thaneither synthetic fertilizers or manures. Some-times the difference in price can be substantial.

Choosing organic fertilizers involvestradeoffs in cost and convenience. Farmyardmanure is usually inexpensive or free, but isless convenient than packaged, commercialmaterials. If you or your neighbors have live-stock it makes both environmental and eco-nomic sense to recycle the manure producedby the livestock.

Packaged organic fertilizers can be ex-pensive, but gardeners may choose themwhere convenience or quick availability ofnutrients is important, or for small gardens

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where little fertilizer is needed. The cost perpound of nutrients in organic fertilizers varieswidely, depending on the type of material, theconcentration of nutrients, and the size of thepackage. Compare costs and nutrient avail-ability when shopping for organic fertilizers.

Lime, Gypsum, and Wood Ashes Lime, gypsum, and wood ashes are all

mineral materials used as organic soil amend-ments. Lime and gypsum are commercialproducts, while wood ashes are producedfrom home woodstoves and fireplaces.

Lime and pH. Lime is ground limestone,a rock containing calcium carbonate. Limeraises the pH of acid soils, and supplies theessential nutrient, calcium. Dolomitic limecontains magnesium as well as calcium, andis a good choice for organic gardeners inwestern Washington, where garden soils of-ten are deficient in magnesium.

In strongly acid (low pH) soils, many nu-trients are less available to plants, and sometoxic metals are more available to plants. This

can be corrected by the proper application oflime. Soils are naturally acidic in humidareas—most of western Washington—and areneutral to alkaline in drier areas—most ofeastern Washington. Fertilizers tend to in-crease soil acidity over time; some easternWashington topsoils have become acidic fromfertilization.

The best way to determine if your soilneeds lime is to have your soil tested. In theabsence of a soil test, western Washingtongardeners can add about 50 pounds of dolo-mitic lime per 1000 square feet of garden peryear. Do not lime areas where you grow acid-loving plants, because they are adapted toacid soils. Lime is a slow-release material.Fall application will benefit a spring crop.

Gypsum (calcium sulfate) is not a substi-tute for lime. It provides calcium and sulfurto soils, but has little effect on soil pH. Gyp-sum has been promoted as a soil amendmentto improve soil structure. In the vast majorityof cases it will not work. Gypsum improvesstructure only when the problem results fromexcess sodium in the soil, a rare condition inWashington. Use organic amendments toimprove soil structure, as described earlier.

Wood ashes are a readily available sourceof potassium, calcium, and magnesium. Theyalso act like lime, raising the pH of the soil.High rates of wood ashes may cause short-term salt injury, so keep applications to lessthan 15-25 pounds per 1000 square feet ofgarden. We do not recommend using woodashes in alkaline soils.

Estimating How Much OrganicFertilizer to Use

Estimating how much organic fertilizer touse is a challenge. We have to estimate boththe amount of nutrients our crop needs, andthe availability of the nutrients in the organicfertilizer. Two standard methods for estimat-ing fertilizer needs are through soil tests andextension bulletins.

Table 5. Total nitrogen, phosphate andpotash content typical of some organicfertilizers.

Material N P2O5 K2O

%

Cottonseed Meal 6-7 2 1Blood Meal1 12-15 1 1Alfalfa 2 0.5 2Bat Guano1 10 3 1Fish Meal1 10 4 0Fish Emulsions1 3-5 1 1Bone Meal 1-4 12-24 0Rock Phosphate2 0 25-30 0

(only 2-3%available)

Greensand 0 0 3-7Kelp Meal 1 0.1 2-5

1These materials contain a substantial amount of quicklyavailable nitrogen that plants can use early in the season.2Very low availability. Useful only in acid soils.

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Soil TestsA soil test will give you the levels of nutri-

ents in your soil and a recommendation forhow much fertilizer to add each year basedon your soil test results and the crops youare growing. You don’t need to test your soilevery year—testing every 3 to 5 years isenough.

Washington State University and OregonState University no longer test soils, but pri-vate labs in both states do tests for gardensoils. Extension county offices have lists oftesting labs. If you have not worked with alab before, call them to make sure they areset up to do soil tests and make recommen-dations for garden soils. Ask the lab:

• If they routinely test garden soils forplant nutrients and pH

• If they use WSU or OSU test methodsand fertilizer guides

• If they give garden recommendations fororganic fertilizers

• How much a test costs• How quickly you will get results

Extension BulletinsIf the cost of a soil test is large compared

with your normal gardening costs, you canestimate your fertilizer needs using exten-sion bulletins instead of soil tests. Thesebulletins usually give recommendations forsynthetic fertilizers. You will need to adaptthese for the lower nutrient availability inmost organic fertilizers.

Tips for Estimating Organic FertilizerRates

• Organic fertilizers having large propor-tions of available nutrients (such as batguano and fish emulsions) can be sub-stituted in direct proportion for syntheticfertilizers.

• For other packaged fertilizers, applyaccording to their nutrient availability.Composts, rock phosphate, and plantresidues generally have lower nutrientavailability than more concentratedanimal products (bloodmeal, bone meal,and high-nitrogen chicken manure).Recommendations on the packageoften are a good guideline for applica-tion rates. Check the recommendationsagainst other products to make surethey seem reasonable.

• The nutrient concentration and avail-ability in manures varies widely depend-ing on the type of manure and its han-dling. Application rates range from 5gallons per 100 to 150 square feet forhigh-nitrogen chicken manure to 1 inchdeep for steer or horse manure compostedwith bedding. Estimate applicationrates based on your manure choice.

• Observe your crops carefully. It is some-times hard to estimate how muchorganic fertilizer to use. Lush plantgrowth and delayed fruiting and flow-ering are signs of high amounts of avail-able nitrogen, and may indicateoverfertilization. You can experimentwith different fertilizer rates in differentparts of a row and see if you noticedifferences. Plan your experiment care-fully, so you are confident that anyresults come from the fertilizer rates,rather than differences in soil, watering,or other management.

• Soil testing also is valuable in under-standing the nutrient status of your soil.Many established gardens have highlevels of soil fertility, and crops will growjust as well using less fertilizer.

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Plant Disease ControlSome people think that controlling plant

diseases always means spraying with chemi-cal pesticides. Pesticides are only one of themany techniques and tools used to combatdiseases. An organic gardener can use manyof the methods available, but also must bewilling to put in extra time and effort to ac-complish the job. A basic understanding ofplant diseases is essential if you are to besuccessful.

Plant Disease PrinciplesA plant disease is a process that harms

all or part of the functions of a plant. It alsomay affect plant structures. It is abnormaland harmful in some way.

Plant diseases are generally divided intotwo groups based on their cause:

1.Nonparasitic diseases are induced bysome cultural or environmental factorsuch as nutrient deficiencies, extremecold or heat, toxic chemicals (air pol-lutants, weed killers, or too much fer-tilizer), mechanical injury, or lack ofwater. These diseases cannot be spreadto healthy plants, and their controldepends solely on correcting the condi-tion causing the disease. Two-thirds tothree-fourths of plant problems fall inthis group of “diseases.”

2.Parasitic diseases are caused by livingorganisms (pathogens), which derivetheir food by growing as parasites uponplants. The most common causes ofparasitic diseases are fungi, bacteria,viruses, and nematodes. Only one-fourthto one-third of plant problems are in thisgroup of diseases.

Fungi are organisms that lack the greencoloring (chlorophyll) found in seed-produc-

ing plants and, therefore, cannot manufac-ture their own food. Between 50,000 and100,000 different species of fungi of manytypes and sizes exist, but not all are harm-ful. In fact, some, such as mycorrhizal fungi,are extremely beneficial to plant growth. Mostare microscopic, but some, such as themushrooms, are quite large. Most fungi re-produce by spores.

Bacteria are very small one-celled organ-isms that reproduce by simple fission. Theydivide into two equal halves, each of whichbecomes a fully developed bacterium.

Viruses are so small they cannot be seenwith the ordinary microscope. Many virusesthat cause plant diseases are transmittedfrom one plant to another by insects, usu-ally aphids or leafhoppers. Viruses also arevery serious problems in plants propagatedby bulbs, roots, and cuttings, because thevirus is easily carried along in the propagat-ing material.

Nematodes are small eel-shaped wormsthat reproduce by eggs. The number of eggsproduced by one female nematode and thenumber of generations in a season dependon soil temperature. Therefore, nematodesusually cause more problems in warmerareas of the country. Most nematodes feedon the roots and lower stems of plants, but afew attack the leaves and flowers.

It is helpful to think of a parasitic plantdisease as a process involving three factors:a host plant, a pathogen (microorganism),and the environment that affects both. Theconcept is illustrated in Fig. 1.

The host plant will have certain char-acteristics, such as being resistant or sus-ceptible to a particular pathogen. In turn,the pathogen will have characteristics thatmake it successful or unsuccessful as a

cause of disease on the particular host. En-vironmental factors (such as moisture, tem-perature, and nutrition) affect both the hostand the microorganisms that cause diseaseand play a vital role in the disease develop-ment process.

Ingredients for a plant disease epidemicwould be a large population of a susceptiblecrop, an abundance of an aggressive patho-gen, weather, and microclimatic conditionsaround the plants that favor rapid develop-ment of the disease. The probable outcomecould be changed only by changing the rela-tionship among the three factors—host,pathogen, and environment. When you beginto change this relationship, you are attempt-ing to control the plant disease. Your successwill depend on many factors, including yourunderstanding of the particular disease andthe management options available.

Methods of CombatingPlant Diseases

Attempts to control plant diseases can befrustrating, expensive, and unsuccessful ifyou do not choose the best method for theparticular plant disease. The phrase, “plantdisease management,” is a realistic descrip-tion because we seldom “eradicate” disease.The incidence and severity of many plantdiseases can be controlled until they are notmajor limiting factors in the production of acrop. As with insects and weed pests, wemust battle plant disease almost every yearon many crops.

ExclusionThis process involves controlling a plant

disease by preventing the introduction of apathogen to an area where it is not alreadypresent. That area can be a country, state,an individual garden, or an area of a garden.

Upon entering this country, and evensome states, you may be asked if you arecarrying living plants, fruits, vegetables, or

plant products. Such inspection is a methodof preventing entry of certain insect and dis-ease pests. Washington has restrictions con-cerning the introduction of certain plants intothis state. When ordering plant materialsthrough catalogs, you may find your orderreturned with a note stating these plantscannot be shipped to Washington. For in-stance, grape plants or cuttings are not per-mitted to enter the state to protect the grapeindustry from the introduction of several vi-rus diseases not yet known to be present inWashington.

Individual gardeners should be sure thatthe plants they put into their own yards areas free from disease as possible. We highlyrecommend using certified planting material,when available. In Washington, certificationprograms on potatoes, strawberries, raspber-ries, and fruit trees are effective in control-ling virus diseases on these crops. Plants willdisplay a state inspection tag if they qualifyfor certification.

EradicationEradication of plant disease organisms

(pathogen) is carried out in a number of ways.Many of these we commonly refer to as “cul-tural control practices.” They include croprotation and sanitation. In most situations,however, we do not actually eradicate theorganism, but reduce it to a level minimiz-ing significant loss.

Crop rotation. Rotating crops is as oldas agriculture and is based as much on su-perstition and art as on scientific fact. Con-tinuous cropping in one area can perpetu-ate and build up pathogenic organisms. Croprotation, however, is not always effective be-cause of the various microorganisms andtheir different capabilities of survival. A 3-to 5-year rotation is suggested for home gar-dens. The rotation should include plants fromdifferent families. Cabbage, cauliflower, andbroccoli, for example, are all related andwould not be considered good choices of se-quence in a rotation. Potatoes, corn, cole

11

1. No disease.

Host

Environment

Pathogen

2. Normal combination of factors requiresno control.

D

EH

P

3. Control by exclusion.Prevent introduction of pathogen.

EH

7. Epidemic level—control needed.

D

6. Control by eradication.Reduce pathogen population by sanitationor crop rotation.

4. Control by resistance.Planting varieties resistant to disease is thebest method of control.

D

EH

P

DE

H

P

5. Control by protection.Modify the environment withcultural or chemical practices.

D E

H

P

Fig. 1. Three factors of parasitic plant disease and levels of control. The disease (D) isrepresented in the areas where the circles overlap.

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crops (cabbage, broccoli, turnips, radishes,cauliflower, etc.), legumes (peas and beans),and leafy vegetables would be examples ofmore logical sequence crops.

Sanitation can be defined as the removaland destruction of diseased or dead plantsor plant parts as soon as the maladies arenoticed. It is a common and effective plantdisease control technique. A reduction in thepopulation of disease organisms results inless chance for serious disease outbreak.Destruction of volunteer plants, overwinter-ing host plants, infected crop residue, anddiseased plants would be good sanitation.

Sanitation in handling vegetativelypropagated materials is of utmost importancein preventing the spread of virus diseases.Remove and destroy virus-infected plants(roguing). These plants cannot be cured. Theyact as potential disease sources.

Pruning diseased twigs and branches ishelpful in controlling diseases such as brownrot, Coryneum blight of stone fruits, anthrac-nose, and European canker of apples. Makepruning cuts well below the diseased area(3-6 inches) to be sure you remove all dis-eased tissue. After cutting into diseasedtissue, disinfect the shears before makinganother cut. Disinfect shears by washingthem with soap and water and swabbing withrubbing alcohol. Also disinfect shears whenyou complete work on each tree. Leave untillast those trees in need of pruning for dis-ease control. This will lessen the chance ofspreading the disease. Destroy pruned-outplant parts.

Fruits such as strawberries, raspberries,or beans which are infected with gray mold(Botrytis) must be destroyed if you want tokeep this disease under control without theuse of fungicide sprays. Raking up and de-stroying leaves infected with apple scab isbeneficial in breaking the life cycle of thisdisease.

Diseased plant materials should not becomposted. Thoroughly hot composting(reaching a temperature of 140°F/60°C) will

inactivate most disease organisms. Incom-plete or cold composting, however, will spreadthe disease.

Controlling weeds also can be importantin preventing disease. Certain weeds can actas a source of inoculum (disease). Wild black-berries, for instance, often are infected withvirus diseases and the bacterium responsiblefor crown gall.

ProtectionFungicides are used in disease control to

protect the plant from infection; thus, theyneed to be applied before the plant is dis-eased. In only a limited number of situationscan fungicides actually cure a plant once itis diseased. However, the fungus that causespowdery mildew is located on the outside ofthe plant and is vulnerable to fungicidesprays after infection has taken place.

Elemental sulfur has fungicidal proper-ties, and some organic gardeners are notopposed to its use. To be used as a fungi-cide, it must be very finely ground. Sulfurfertilizer is coarse and will not act as an ef-fective fungicide. Sulfur, available as a fun-gicide, can be applied either as a dust ormixed with water and applied as a spray.Plant damage can result if elemental sulfuris used when temperatures are above 85°F/29°C. (See warning for elemental sulfur un-der Insect Management). Lime sulfur is ac-ceptable as an organic material and is com-mercially available.

Copper fungicides also are acceptableto some organic gardeners. Bordeaux mix-ture (a mixture of copper-sulfate and lime)and fixed coppers (such as Microcop) areavailable to home gardeners. If you chooseto use any of these fungicides, be sure tofollow label directions and precautions anduse them only on plants indicated on thelabel.

There are nonfungicidal methods to pro-tect plants from disease. These generallyinvolve avoiding situations that favor plantdisease development.

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Planting site. Choosing the right plant-ing site is important. This involves wide geo-graphic considerations, as well as specificsites in a yard or garden. For example, be-cause of the severe disease problems on apri-cots, cherries, and peaches (Coryneumblight, brown rot, bacterial canker, and peachleaf curl), the fruits are not easily grown inwestern Washington. The drier, warmer cli-mate of eastern Washington is the place togrow these fruits. Small fruits offer anotherexample: raspberries require soils with ex-cellent drainage to avoid root rot problems.Good winter water drainage is as importantas summer drainage. In contrast, blueber-ries tolerate wet soils.

Planting date. Date of planting also caninfluence disease development. Planting tooearly, especially pumpkin or squash, can leadto seed rot and damping-off of young seed-lings. Delaying planting until the soil haswarmed allows the young plants to growfaster and, thus, avoids rotting organisms.On the other hand, planting peas early avoidsvirus disease problems. Aphids, which trans-mit these viruses from clover-type plants topeas, are not active during the early part ofthe growing season; thus, the peas avoid in-fections by developing before exposure to thevirus-carrying aphids.

Planting conditions. Good air circulationand light penetration help avoid the humidconditions that promote disease. Overcrowd-ing creates micro-environments favoringplant disease.

Fertilization. Properly fertilized plants aregenerally more resistant to disease thanthose under nutritional stress. Overfertil-ization, leading to an abundance of soft, luxu-riant growth, also may lead to disease losses.

Moisture. Avoid diseases by proper wa-tering. Avoid using overhead irrigation (ap-plying water through sprinklers which wetthe leaf surfaces) when possible. Applying

water directly to the soil surface by diggingfurrows adjacent to rows, and using soakerhoses are better alternatives. If you must useoverhead sprinklers, water in the morningso the foliage has a chance to dry beforeevening. Late afternoon watering allows thefoliage to remain continuously wet through-out the night, a practice which invites disease.Most infective propagules (such as fungusspores) which initiate plant disease requiremoisture to germinate and cause infection.Thus, cultural practices that help foliagebecome dry or remain dry aid in control ofplant disease, especially foliar diseases.

Handling. Proper handling before andafter harvest can prevent rots from certaindiseases. Late blight of potatoes is a goodexample of a harvest disease. Late blight notonly causes a severe foliage disease, but alsoresults in a storage rot if the tubers becomeinfected. Tubers get infected during harvestwhen they contact the fungus on the diseasedvines. To prevent tuber infection cut the vinesand remove from the area 10-14 days beforeharvesting tubers. Cut the vines an inch orso below the soil surface. Not only will thetubers not contact the disease, but this 2-week curing period promotes a tougheningof the potato skins which will help preventwounding during harvest.

Another example of harvest disease isBotrytis gray mold, which can be responsiblefor rotting of berries before or after they havebeen picked. This postharvest rot can beavoided by picking the berries during coolparts of the day, by keeping picked fruit outof the sun, and by placing them in cool stor-age as soon as possible. They should not bewashed until they are ready to be consumedor processed, since moist surfaces allow ger-mination of the spores of rotting organisms.

Soil pH. Soil acidity also can influencethe development of certain diseases. Potatoscab, for instance, is most severe in soils thathave a neutral to alkaline pH. Thus, additionsof lime, wood ashes, and manure increase

14

the severity of potato scab. Club root of cab-bage and other cole crops, acts in just theopposite manner. Applications of lime havereduced the severity of this fungus disease.

Genetic ResistanceChoosing crop varieties resistant to one

or more pathogens is the most economicaland desirable way to avoid disease losses.When selecting varieties for disease resis-tance, it is important to know whether thedisease is a potential problem in your area.For example, apple varieties resistant to fireblight are desirable in eastern Washington;since the disease is essentially never a prob-lem in western Washington, fire blight resis-tance is not a criterion for selecting a varietyto grow there.

Locating information on disease resis-tance often is difficult and sometimes impos-sible. Generally, seed catalogs and othersources will advertise certain varieties ashaving specific disease resistance. If this in-formation is not given, assume the variety issusceptible. Treat cautiously a general state-

ment that a variety has good disease and pestresistance. The resistance it possesses mayhave no application to the disease problemsin your area.

Small Fruit Disease ResistanceMany varieties of berry fruits can be grown

in Washington. Each, however, has a differ-ent tolerance to various diseases. Tables 5and 6 and the following section summarizethe information available on small fruit dis-ease resistance.

Black RaspberriesBlack raspberries are subject to several

diseases that cause rapid deterioration ofindividual plants and seriously limit theproductivity and life of the plantings. The dis-eases include Verticillium wilt, anthracnose,and streak, mosaic, and curl viruses. Breed-ing and testing go on continuously through-out the United States to develop or find vari-eties resistant or tolerant to these diseases.Results have not been successful.

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Table 5. Tolerance of strawberry varieties to disease.

Disease Plant tolerance Variety

Viruses Tolerant Shuksan, Totem, Benton(aphid transmitted) Intermediate Rainier

Susceptible Hood, Quinault

Red stele root rot Resistant Quinault, Hood, Totem, Rainier,Shuksan, Benton

Gray mold Least susceptible Shuksan, TotemModerately susceptible Hood, Rainier, Benton

Powdery mildew Tolerant Hood, Totem, Benton, TristarModerately susceptible ShuksanVery susceptible Quinault, Redcrest

Verticillium wilt Resistant TristarSusceptible Vesper*Very susceptible Earlidawn*

*Varieties adapted to eastern Washington.

In the past, many people grew good gar-dens using few, if any, insecticides. While afew of our pests are recent imports from othercountries, for the most part we face the sameinsects found here before synthetic insecti-cides were developed. New approaches toinsect management have evolved. These,combined with many old-time mechanicaland cultural practices, make it possible togrow reasonably pest-free garden producewithout using synthetic insecticides.

Most seasonal gardeners use a decision-making process called Integrated Pest Man-agement (IPM), whereby they continuouslymonitor for pests. When a pest is discovered,have it accurately identified and learn aboutits life cycle, behavior, and host crops. Thisinformation allows choosing effective man-agement methods and timing them properly.Then, if unacceptable damage occurs, youcan employ these methods to suppress thepest to tolerable levels.

Gardening successfully without syn-thetic insecticides requires more knowledgeon the part of the gardener. It may alsorequire additional work, since many alter-native pest management approaches are la-bor intensive. Organic gardeners should bewilling to accept some produce less perfectthan that from gardens or farms which em-ploy pesticides.

Alternative pest control methods may bebiological, cultural, mechanical, or a natu-ral, less toxic insecticide. A gardener often

Insect Managementuses a combination of approaches to solve apest problem. These alternative methods aredescribed below.

Biological Control ofInsect and Mite Pests

Biological control is the use of any formof life to control a pest. A controlling agentmay be a disease organism, a predacious orparasitic insect, predacious spiders andmites, insect-feeding birds, rodents, toads,or any other vertebrates. A number of com-panies now supply insect and mite predatorsand parasites to gardeners. For a current andcomplete listing, refer to magazines on or-ganic gardening. Your Extension office mayhave partial lists. Many of these beneficialorganisms occur naturally, but often effec-tive numbers develop too late to control thepest before severe damage occurs. Keep inmind that when introducing an insect to preyupon or parasitize a pest, its numbers onlycan increase in nature if it has sufficient preyto feed upon. If you are experiencing littleinsect damage or the pest species are in lownumbers or absent, the beneficial organismsmust move elsewhere, where food is avail-able to survive.

To allow beneficials that feed on pests toincrease in number sufficiently to controlpest insects, you must accept a certain

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Table 6. Tolerance of red raspberry varieties to root rot.

Tolerance level Variety

Tolerant Newburgh, Sumner, LathamSusceptible Willamette, Meeker, Chilcotin, Heritage, TulameenVery susceptible Canby, Skeena, Comox

amount of insect damage. You can’t haveinsect-free garden produce and encouragebeneficial insects at the same time. Releas-ing predators or parasites can be highly ben-eficial in establishing them in new areas.

Biological control is seen as three differ-ent approaches: conservation, augmentation,and classical (introduction) biological con-trol. Conservation is seen as “protecting”what is already there. This is achieved byencouraging native, natural enemies throughproviding a “user friendly” environment (i.e.,using selective natural insecticides such asBacillus thuringiensis). Augmentation is seenas adding to what is already there or shouldbe there (i.e., purchasing and releasing natu-ral enemies). Classical biological control isthe releasing of foreign beneficials to controlintroduced pests in areas where their natu-ral enemies do not exist (i.e., cinnabar mothto control tansy ragwort). Gardeners can anddo use conservation and augmentation com-monly. Classical biological control is normallycarried out by government agencies.

A number of beneficial organisms are be-coming available to home gardeners. Themore important of these and some of the in-digenous natural enemies are discussedhere.

Lady BeetlesOrganic gardeners have long used lady

beetles as an approach to aphid control. Theprocess includes purchasing the beetles inbulk quantities and releasing them at thesite. The idea is a good one; however, aspectsof the beetle’s biology thwart the total effec-tiveness of such a practice. These beetlesoverwinter as adults in large masses in theforests or hillsides. They are collected at thistime and kept in cold storage until they aresold. The beetles often are released in largenumbers on a single site (backyard) and ex-pected to remain. The aphid population fre-quently is not large enough at the time ofrelease to support such a population of ladybeetles, so they do what any hungry animalwould do under such circumstances, they

leave the area in search of sufficient food.Many entomologists believe most species oflady beetle must undergo a dispersal flightafter overwintering before they settle down,mate, and lay eggs. This is a phase missingin the beetle at the time of purchase. Whenreleased they take flight and leave the area.Thus, the beneficial effects are only realizedby unknowing, nonpaying neighbors. Somegrowers have used this technique for manyyears. Since several are doing so on an area-wide basis, they apparently are achievingsuccess accidentally by trading beetlesthrough random multi-directional dispersalflight.

Predator Mites1

Several species of predator mites feed onharmful plant-feeding mites. The most com-mon beneficial mites include Typhlodromus,Phytoseiulus, and Amblyseius species. Thesetiny predator mites are usually smaller (about1/100 to 1/50 inch long) than the plant-feed-ing mites, two-spotted mite, and Europeanred mite upon which they feed. They usuallyare teardrop shaped and yellowish or clearin color. Beneficial mites overwinter as adultfemales on trees and in soil debris. Theybecome active in April and May and beginto feed on available prey. Female mites con-sume about 70 to 80 prey during their 6-weeklifetime. Ten or more generations can be pro-duced per year. Several predator mite speciesare available commercially.

Predacious Ground Beetles1

Predacious ground beetles, or carabids,are large beetles (1/4 to 11/4 inch), usuallyblack or dark metallic in color. Most specieshave the same characteristic shape. Elon-gate and wormlike larvae are fast moving.They capture prey with large mandibles. Bothlarval and adult stages feed at night on avariety of insects such as cutworms and

1Adapted from PNW343 Beneficial Organisms Associated withPacific Northwest Crops

17

maggots. Some species also feed on snailsand slugs. Adults are the wintering stage,and larval development takes about 1 year.Carabids forage in most Northwest gardens.

Green Lacewing1

Adult lacewings (Chrysopa spp.) are lightgreen. They have two pair of large membra-nous netlike wings. They usually are 1/2 to3/4 inch long. Adults feed on aphid honey-dew and plant fluids. The larvae reach 1/3inch long at maturity and resemble tiny lightbrown alligators. They feed primarily onaphids, capturing them with their sicklelikemandibles. Each lacewing may consume asmany as 750 aphids during its larval stages.Several generations are produced each sea-son. Lacewings are available commercially.

Syrphid Flies, Flowerflies1

These brightly colored flies closely re-semble bees and wasps but do not sting. Theadults often hover around flowers, where theyfeed on nectar and honeydew from aphidsand scale insects. The blind sluglike larvaeusually are pale green to brown and charac-teristically tapered toward the head.Throughout the growing season the larvaefeed on aphids and other soft-bodied insects.Black oily smears of excrement on plant foli-age are typical signs of syrphid fly feeding.Many generations occur each year. Syrphidsare not yet available commercially.

Aphid Parasites1

These small (less than 1/4 inch), solitarywasps parasitize and kill aphids. Their lifecycle is closely synchronized with that of theirhost. The adult female wasp deposits an egginside an aphid host. The hatching wasplarva eventually kills its host by consumingits internal tissues and organs. The deadaphid “mummy” has a bloated look, appearsbronze or gray in color, and is quite distinct

from unparasitized aphids. Inside the aphidmummy, the mature wasp larva spins a co-coon in which to pupate, and emerges as anadult through a hole on the top part of theaphid. Numerous overlapping wasp genera-tions occur each season. The wasps do notbite or sting people. Many of these wasp spe-cies are available for purchase.

Fungi1

Insects are susceptible to attack by manynaturally occurring disease organisms suchas fungi, viruses, bacteria, and protozoa.Because aphids have sucking mouthparts,they are commonly attacked by fungal dis-eases. The germ tubes produced by fungalspores penetrate their host directly. You caneasily recognize aphids killed by a fungalepidemic. They will be attached to a leaf andappear fuzzy or “moldy.” Fungus epidemics,limited by moisture and temperature, gen-erally do not occur unless relative humidityis greater than 90%. A few commercially de-veloped fungi are available for aphid control.Gardeners may notice naturally occurringepidemics of fungi, which can kill entireaphid populations. Some common fungi in-clude Beauveria, which attack beetles, andEntomophthora, which attack flies and grass-hoppers.

At least one commercial fungal agent isavailable for controlling certain insect pests.Always read the label to see what plants youmay use controls on.

Nematodes1

Insect-parasitic (entomopathogenic)nematodes attack and kill insects, primarilythose living in soil. The nematodes enter in-sects through natural body openings andrelease bacteria into the insect’s body cav-ity. The bacteria kill the insects, and thenematodes then multiply by eating the insectcadavers and the bacteria. Insect-parasiticnematodes are available commercially.

1Adapted from PNW343 Beneficial Organisms Associated with Pacific Northwest Crops

18

Follow label directions for the temperatureand moisture requirements of the nema-todes.

Other BeneficialsYou will run across many other beneficial

insects and spiders. These include tachinaflies, whose larvae are internal parasites ofcertain caterpillars; many predacious bugs(damsel bugs and pirate bugs) overcome preywith their powerful forelegs and suckingbeaks. Various crab and wolf spiders alsoadd to the array of beneficials in the garden.Always observe the behavior of these insectsand their relatives to see what they’re doing.They often turn out to be beneficials, or atleast harmless to plants.

Insect Disease OrganismsStrains of bacteria called Bacillus

thuringiensis (B.t.) produce a toxin that killsmany caterpillar pests. The insecticidal toxinis sold under various trade names. There arestrains of this bacteria specific to fungus gnatand mosquito larvae. Another strain is spe-cific to elm leaf beetle and the Colorado po-

tato beetle. Buy the appropriate strain of B.t.to control the target pests. Since B.t. is es-sentially a stomach poison, apply it when thetarget pests are in feeding stages. Targetpests are controlled more completely whenthey are treated as young larvae.

BirdsBirds are far more important in prevent-

ing insect outbreaks than in controllingthem. All bird species feed on insects to somedegree. The fly-catchers, swallows, warblers,vireos, creepers, nuthatches, and woodpeck-ers are almost entirely insectivorous, whileblackbirds, robins, crows, gulls, magpies,and even the birds of prey—the hawks andowls—commonly feed on insects.

To develop bird numbers near gardens,encourage those species which feed largelyon insects. If you encourage all species ofbirds, including those which damage gar-dens, such as starlings and blackbirds, youmay be asking for trouble. Encourage insect-feeding birds by providing cover, water,supplementary feed (particularly during win-ter and spring), and discouraging cats andother predators.

Bug Juice Sprays

“That plants and animals commonly die of disease without human intervention isobvious to gardeners. It is the basis for the folk pest control recipe for grinding upsick or dead insects and spraying the bug juice to spread the pathogens (microor-ganisms that cause the disease) and kill more pest insects. However, sprayinghomemade bug juice around your house may not be a good idea since some mi-croorganisms and fungi found on the dead bodies of insects are pathogenic tohumans and might get into the “juice.” But the idea of using microbes that causedisease in plants and insects to control pests is not a bad one. A number of suchmicrobial products are available commercially.”

Olkowski, Daar and Olkowski. 1991. Common-Sense Pest Control: Least Toxic Solutions for YourHome, Garden, Pets and Community.

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Attract insectivorous birds to your homeby planting ornamentals that provide suit-able bird cover and food. Some especiallyvaluable plants are

Dogwood (Cornus spp.)Mountain Ash (Sorbus spp.)Russian Olive (Elaeagnus spp.)Firethorn (Pyracantha spp.)Crabapple (Malus spp.)Elderberry (Sambucus spp.)Cotoneaster (Cotoneaster spp.)Western Red Cedar (Thuja plicata)Sumac (Rhus spp.)Holly (Ilex spp.)Hawthorn (Crataegus spp.)Highbush Cranberry (Viburnum trilobum)Cherry and Wild Plum (Prunus spp.)Serviceberry (Amelanchier spp.)

The Washington State Department of Fishand Wildlife has many useful publicationsthat address backyard wildlife sanctuaries.One in particular that will help you to en-courage desirable birds is called Nest Boxesfor Birds.

Besides encouraging wild birds, somegardeners use domestic fowl for pest control.Chickens, ducks, and geese eat insects withgreat relish. They also eat slugs and manyweeds, so they can be wonderful garden helpers.

Manage the domestic birds carefully. Ifthey have access to vegetables such as let-tuce and spinach, they will eat your crop.Keep them away from small or tender plants,since they can trample and break plants.

Some have employed geese in commercialorchards and small fruit farms. In strawberryfields, remove them during fruit season, sincethey love the berries.

Chickens usually are allowed access togardens between crops. They weed, eliminateevery insect they can scratch out of the soil,and fertilize—all at the same time. Some gar-deners have experimented with “chickentractors.” These are small, portable, hen-houses with attached runs. The outdoor runis built the exact same size as the gardener’s

vegetable beds. The “tractor” is moved frombed to bed as the soil needs the attention ofthe chickens.

Domestic fowl need proper care and feed-ing. They also need your protection. Birdsallowed to forage may be preyed upon bydogs, raccoons, or coyotes.

Cultural and MechanicalControl of Insect

and Mite PestsMany cultural practices reduce the sus-

ceptibility of garden plants to insect attack.In many instances mechanical devices orphysical destruction work well. Here aresome of the more popular techniques.

1. Rotate your garden plot. This is easierif you have a large property, but evenin a small garden you can change thesequence of plants grown in differentareas. Try to grow a particular crop ina bed or section of the garden no moreoften than one year out of three. Rotateby plant family (cabbage family) orgroup (root crops). Should you developa soil problem, such as wireworms orwhite grubs, you may want to use evenlonger rotations before growing tuber orroot crops, (potatoes or carrots).

Avoid or restrict growing insect-sus-ceptible crops. Unfortunately, we haveno nonsynthetic insecticides suitable forsoil insects. White grubs, wireworms,cabbage maggots, onion maggots, car-rot rust fly, and other soil insects maycontinue to bother you unless you usefallowing or exclusion techniques whereappropriate.

2. Fertilize, cultivate, and water well toinduce good, healthy growth. Insectinjury is less damaging on a healthyplant. Note: Fast release of high nitrogenfertilizers can lead to aphid, scale, orwhitefly problems. Using slow-release

20

fertilizer with a moderate proportion ofnitrogen may minimize these pestproblems.

3. Use interplantings (as opposed to solidplantings of a given species) to isolatethe infestation and reduce damage.

4. Handpick and destroy pests whenfeasible by knocking pests from foliageinto a bucket containing a mixture ofwater and soap. Remember many gar-den pests are nocturnal, so you mayhave to do this at night using a flash-light.

5. Use transplants. The longer a plant isgrowing in a garden, the greater itsexposure to potential insect attack.Plants of the cabbage family will avoidearly and often devastating attacks ofcabbage maggot if you purchasehealthy, mature transplants. A healthytransplant will more likely overcomesubsequent insect attack than a smallplant developing from seed in the garden.

6. Practice sanitation. Since many gardeninsects overwinter in plant debris, spadeunder old plants, (spinach and lettuce)during the summer, or add these plantresidues to your compost. The cabbageaphid, for example, may overwinter asan egg on the cabbage plant; the adultasparagus beetle overwinters in thehollow stems of asparagus; and severalspecies of leafhopper overwinter in oron plant debris. Immediately dispose ofyour reject onions, since the onionmaggot will continue to breed in them.Whenever a garden plant is no longerproducing, spade it in or relegate it tothe compost pile.

Keep your garden free of weeds andvolunteer plants: these can harborpests—particularly certain aphids whichmay transmit disease organisms. Tallgrasses and weeds that border yourflower or vegetable garden provide goodcover for slugs, so keep the grass andweeds trimmed. Piles of rocks, woodstacks, or old pots also can harborslugs.

7. Cultivating a garden exposes pests thatlive near the soil surface to birds andinjures or kills some insects. Fall culti-vation also exposes pests to the rigorsof winter.

8. Planting your crop prior to emergenceof a particular pest or late planting toavoid resident first generations of thepest can reduce but not necessarilyeliminate damage. For example, plantingpeas early can help reduce crop loss dueto viruses transmitted by pea aphid insusceptible varieties. Check with yourlocal authority on this approach sincepest populations often peak at differenttimes depending on geographicallocation.

9. Certain colors attract some insects. Youcan use this behavior against them. Aneffective example is capturing whitefliesin greenhouses where yellow cards orboards are hung every few feet amongthe plants and covered with sticky sub-stances. Whiteflies are attracted to theyellow card and become stuck on theboard. In many instances 100% controlof whiteflies is not necessary (hobbygreenhouses). Most plants can toleratea low level of whiteflies. Heavyweightmotor oil (SAE 90) also is an effective

Figure 2. Sticky yellow card for trappingwhiteflies and fungus gnats.

21

trapping material and is easier to wipeoff the boards. This may work on white-flies outdoors, although tests have notbeen conducted to determine the effec-tiveness. These traps also catch asubstantial number of fungus gnats.

10. Use trap crops. Pests prefer some plantsmore than those in your vegetable gar-den. Use them to steer pests away fromyour more desirable plants. Forexample, certain aphids populatenasturtiums before they move ontoother susceptible plants. Destroyaphids on the nasturtiums before theybecome abundant, or they will overflowonto other garden plants. This tech-nique often works.

11. Row or bed covers, wire, nylon, ormuslin screen cages are useful ingarden plots for excluding many insectsfrom the crops they normally infest.Lightweight fabric, sometimes calledfloating row cover, is especially easy touse since it does not require any sup-port frames. These row covers have beeneffective at keeping cabbage maggotsfrom cole crops, radishes, or turnips;carrot rust fly from carrots and pars-nips; and spinach leafminers from spin-ach, chard, and beet tops. They also can

be used to keep out pea leaf weevils untilseedling peas have reached the four– tosix–expanded leaf stage, at which pointthey are tolerant to weevil. Note: Rowcovers can make your pest problemworse if you employ them on alreadyinfested soils where the pests have over-wintered. They only can be used effec-tively on sections of garden where thepest did not occur the previous year, souse them in conjunction with carefulcrop rotation. (Hotcaps designed toenhance heat conditions will accom-plish the same end if built right.)

12. Stale beer placed in cans sunk in thesoil is attractive to slugs, which find thecontainers, crawl in, and drown. Thismaterial can be attractive to many in-sects, including beneficial ones such ascarabid ground beetles. To protectthese, leave a one-inch rim above thesoil line. The best way to control slugsis still to eliminate their hiding places(tall grassy or weedy areas).

13. Plant “sleeves.” Milk cartons with bothends cut out and placed snugly in thesoil enclosing the plant will serve as aphysical barrier to many pests. Foradditional protection apply a band ofsticky or greasy material, like Vaseline,to the exterior of the carton.

14. Other “insect barriers” are useful ifsome part of the known biology orbehavior of the pest in question lendsitself to manipulation by these methods.For example, most root weevils are nightfeeders. As day approaches, they dropoff rhododendrons and other hostplants to the litter below, where theyhide. They do not fly. If the main trunkis the only access to crawling back upthe plant to feed on foliage, the trunk isan ideal place to consider a barrier.Wrap a strip of plastic or plant wrap-ping paper snugly around the base ofthe trunk with a sticky material for anefficient barrier to root weevils. Checkthe strip from time to time, since debris

Fig. 3. The use of floating row covers canreduce the presence and damage of suchpests as cabbage root maggots by 100%.

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and insect accumulation will make itineffective over time. Remove duringwinter.

15. Resistant varieties. Many plant specieshave varieties that are moderately orhighly resistant to plant pests. Unfor-tunately, many are not available to orknown by name to the home gardener.See EB0970, Root Weevil Control onRhododendrons, for species and variet-ies of rhododendrons and azaleas thatdemonstrate resistance to root weevils.

Pest-plant relationships for straw-berries and raspberries follow.

Strawberry. Strawberry varieties havelittle resistance to major pests such asroot weevils and aphids. However, re-sistance to the two-spotted spider mitehas been found in the Linn variety. Allother varieties are susceptible. TheTotem variety is extremely susceptible.

Raspberry. Red raspberry has littleresistance to the major pests. However,resistance to the raspberry aphid, aninsect which spreads virus diseases,

can be found in Canby, Haida, Skeena,and Nootka varieties.

16. Water. A stream of water from a hosewill control aphids on certain gardenplants. The force of the well-directedspray will kill or dislodge the aphids.Those that are dislodged but withstandthe force rarely make it back to the hostplant. Include this method regularly inyour normal gardening operations. Donot spray plants with water at night ifthey are highly susceptible to foliardiseases. Spray during the daytime sofoliage has a chance to dry rapidly.

17. Other methods. Some publicity favorslight traps, reflective materials, such asaluminum foil, irradiation, electricshock, repellents, and the use of sexlures (pheromone traps). We cannot rec-ommend these methods at present.Eventually they may be of considerablevalue. Combination light traps and elec-trocution grids are fascinating as apotential insect control tool. In the gar-den area, they only serve to “pull” inpests from neighboring gardens. Recentreports indicate that they kill an extraordinary number of beneficial insects.

Companion Planting

“Many gardening books and magazines have published lists of plants that aresaid to protect neighboring plants by repelling pests, a concept sometimes calledcompanion planting. Research in this area has been limited but it has consis-tently shown no overall benefits under controlled conditions. For instance, Uni-versity of California research showed that while a cabbage plant surrounded byfour companion plants of various herbs had fewer imported cabbage worm eggslaid on it than a control plant not surrounded by herbs, yield reduction was se-vere due to the close proximity of the herb plants and competition for resources.When the number of companion plants per cabbage was reduced to two, the herbsgave no significant pest protection and yields were still substantially lower.”

Mary Louse Flint. 1990. Pests of the Garden and Small Farm: A Grower’s Guide to UsingLess Pesticide.

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Natural InsecticidesThe most commonly used natural insecticidesand miticides are listed and discussed brieflybelow. These materials are “natural” inas-much as they are derived from plants andbacteria or from elements taken from nature.

PyrethrinsPyrethrins derive from the dried flowers of aspecies of Chrysanthemum and have beenused for controlling insects since ancienttimes. Since they provide “quick knockdown”and have very short residual effects, theymust be used often. They frequently are soldwith an activator or synergist (piperonyl bu-toxide or peperonyl cyclonene). The use ofpyrethrins without these low hazard and safeactivators would be much less effective, dif-ficult to obtain, and almost prohibitive incost. The pyrethrins kill insects only by con-tact. They are effective against a wide rangeof garden pests, especially the soft-bodiedforms, but will not control mites. Do notspray around fish ponds. Consult the labelfor specific usages.

NeemHundreds of products come from the seeds

and bark of the neem tree. At least one prod-uct is a fungicide. The active ingredient bestknown as an insecticide is azadirachtin. It isextremely safe for humans and pets. It canact as a contact poison, a systemic, or agrowth regulator (interferes with normal molt-ing). Neem products are effective against manycaterpillars, flies, whiteflies, scales, and some-what effective on aphids.

Dormant and Summer OilsPetroleum oils were used for insect con-

trol as early as 1787 and are still popular,although not used as extensively as they

might be. Apply them only on woody plants.Two principal types exist: the dormant oilsonly should be applied on trees or shrubs inthe dormant or delayed-dormant condition;summer oils can be used during the growingseason but also are restricted to woodyplants. Applying a strictly dormant oil dur-ing the growing season will severely burnfoliage. For summer use, purchase oil espe-cially prescribed for this purpose and applyonly on those plants for which the materialis recommended. Some special oils can beapplied either summer or winter; however,the concentration used in summer is far less.

Oils control many insects and their eggs,such as overwintering leafroller, aphid andmite eggs, as well as nymphs and adults ofaphids, scale insects, and mites. Dilute theseoils first with water. They contain emulsify-ing agents that allow them to mix when addedto water. The oils cause little or no harm tomost beneficial insects. Pests rarely developresistance to these sprays. Used correctly,they are nonhazardous to human health. Donot apply oils during freezing weather.

Lime-SulfurLiquid lime-sulfur is an “old timer” that is

still in use. Use it much the same as for thedormant oils diluted with water. Do not ap-ply to apricot trees at any time; you may in-jure the foliage. Use only on woody plantsand only during the dormant season, or upto prebloom on some plants. The only ex-ception is on caneberries where it can be usedfor dryberry mite and redberry mite in thespring when vegetative buds are 1/2 inchlong. This material is particularly effectiveagainst pearleaf blister mites, rust mites andtheir close relatives, as well as for many in-sect eggs. These sprays also have fungicidalvalue. On fruit trees, lime-sulfur often ismixed with dormant oil to increase its effi-ciency. Use lime-sulfur with caution whenyou treat ornamentals near your house. The

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spray drift when dried is difficult to removefrom buildings and may cause stains onpainted surfaces.

Elemental SulfurA finely ground powder, elemental sulfur,

can be applied either as a dust or spray. Inaddition to controlling fungus diseases, italso will give some control of spider mites,especially during hot weather. Warning: ifyou plan to can the produce, do not use sul-fur on most vegetables just before harvest.Small amounts of sulfur in the “preserve” willproduce sulfur dioxide which can cause thecontainer to explode. It also may cause off-flavor. Sulfur can be used safely on berriesand other fruits without these hazards andon vegetables eaten fresh, dried, or processedfor freezing. Sulfur is very safe—in fact, it isan element essential for good health.

SoapsSoap diluted with water has been recom-

mended for certain soft-bodied insects, suchas aphids, since 1787. Most often these natu-ral soaps were derived from either plants (co-conuts, olive, palm, cotton seed) or from ani-mal fat (whale oil, fish oil, or lard). House-hold soaps vary tremendously in composi-tion and purity; also in effectiveness andpotential to harm crops. Use soaps specifi-cally registered and sold for use as insecti-cidal soaps.

Spinosad

This organic insecticide is produced byan actinomycete fungus, Saccharapolysporaspinosa. It is used for managing certainLepidoptera, such as cabbageworm, cabbagelooper, diamondback moth, armyworm, andcutworm. It has a low toxicity to fish, birds,and wildlife in general. However, it is toxic

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Certified Organic ProduceMost organic gardeners supplement their

harvest with fruit and vegetables purchasedat the store. Many retail outlets carry clearlyidentified organic products in separate sec-tions of the fresh, frozen, or canned goodaisles. In addition, many Farmers Marketvendors sell organic produce. To obtain listsof local Farmers Markets in your area, go to:http://www.wafarmersmarkets.com/ andclick on Market Directory. Other sources fororganic produce are Community Supported

Garlic Sprays

“Modern studies confirm that garlicoil exhibits antibacterial, antifungal,amebicidal and insecticidal quali-ties...”

“..although garlic does kill pest insectsand some pathogens, it also kills ben-eficial insects and microbes. Thus wedo not recommend it as an all-pur-pose spray for garden use.”

“We do not recommend garlic foraphid control since it kills the natu-ral enemies of the aphids as well asthe pests; insecticidal soaps are pref-erable.”

Olkowski, Daar & Olkowski. 1991. Com-mon-Sense Pest Control: Least Toxic So-lutions for your Home, Garden, Pets andCommunity.

to bees for three hours following treatment,so do not apply to blooming plants duringthe day.

Agriculture (CSA) farms. These farms sell“shares” which entitle buyers to weekly de-liveries of fresh produce during a definedseason. For a list of CSA farms in westernWashington, go to the Seattle Tilth web site,http://www.seattletilth.org, and click on theannually updated Community Supported Ag-riculture Directory.

The Washington State Department of Ag-riculture (WSDA) Organic Food Program ischarged with certifying organic farms in thestate. They maintain a list of certified pro-ducers which can be found at: http://ag r .wa . g o v/FoodAn ima l/Organ i c/default.htm.

For more information on certification pro-cedures or about how to become certified,contact:

Organic Food ProgramWSDAPO Box 42560Olympia, WA 98504-2560(360) 902-1805

Selected ReferencesHome Gardens. A.L. Antonelli, R.S. Byther,

S.J. Collman, R.E. Thornton, and R. VanDenburgh. Washington State UniversityCooperative Extension EB0422. 1988.26 pp.

Orchard Pest Management—A Resource Bookfor the Pacific Northwest. Eds. E.H. Beers,J.F. Brunner, M.J. Willett, and G.M.Warner. Pub. Good Fruit Grower WA. St.Fruit Comm. 1993. 276 pp.

Growing Small Fruits for the Home Garden.C.A. Brun. Washington State UniversityCooperative Extension EB1640. 30 pp.

Pests of the Garden and Small Farm—A Grow-ers Guide to Using Less Pesticide. M.L.Flint Univ. CA.-Div. Of Agric. and Nat. Res.1990. 287 pp.

Common-Sense Pest Control—Least Toxic So-lutions for Your Home, Garden, Pets, andCommunity. W. Olkowski, S. Daar, H.Olkowski. Tauton Press. 1991. 715 pp.

Beneficial Organisms Associated with PacificNorthwest Crops. R.L. Stoltz, H.W. Homan,C.R. Baird, and R.L. Johnson. PacificNorthwest Extension Bulletin PNW343.1994. 8 pp.

Using horticultural spray oils to control or-chard pests. Willett, M. and P.H.Westigard. Pacific Northwest ExtensionBulletin PNW328. 1998. 8 pp.

Online Resources:

HortSense Fact Sheets.http://pep.wsu.edu/hortsense

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College of Agricultural, Human, and Natural Resource Sciences

Use pesticides with care. Apply them only to plants, animals, or sites listed on the label. When mixing and applying pesticides,follow all label precautions to protect yourself and others around you. It is a violation of the law to disregard label directions. Ifpesticides are spilled on skin or clothing, remove clothing and wash skin thoroughly. Store pesticides in their original contain-ers and keep them out of the reach of children, pets, and livestock.

WSU Extension bulletins contain material written and produced for public distribution. You may reprint written material, pro-vided you do not use it to endorse a commercial product. Alternate formats of our educational materials are available uponrequest for persons with disabilities. Please contact the Information Department, College of Agricultural, Human, and NaturalResource Sciences, Washington State University for more information.

You may order copies of this and other publications from the WSU Bulletin office, 1-800-723-1763, or online http://pubs.wsu.edu

Issued by Washington State University Extension and the U.S. Department of Agriculture in furtherance of the Acts of May 8and June 30, 1914. WSU Extension programs and policies are consistent with federal and state laws and regulations onnondiscrimination regarding race, sex, religion, age, color, creed, national or ethnic origin; physical, mental or sensory disabil-ity; marital status, sexual orientation, and status as a Vietnam-era or disabled veteran. Evidence of noncompliance may bereported through your local WSU Extension office. Trade names have been used to simplify information; no endorsement isintended. Revised August 2004. C. Subject code 262, 200.

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