T E R Y L R . R O P E R , D A N I E L L . M A H R , PA T R I C I A S . M C M A N U S

GROWING APPLESIN WISCONSIN

A3565

Malus x domestica

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CONTENTS

The apple tree . . . . . . . . . . . . . . . . . 2

Site selection and preparation . . . . . . . . . 3

Cultivar selection . . . . . . . . . . . . . . . 3

Rootstock selection . . . . . . . . . . . . . . 4

Planting . . . . . . . . . . . . . . . . . . . 4

Mineral nutrition . . . . . . . . . . . . . . . 5

Weed management . . . . . . . . . . . . . . 5

Training and pruning . . . . . . . . . . . . . 6

Harvest . . . . . . . . . . . . . . . . . . . 10

Storage . . . . . . . . . . . . . . . . . . . 11

Insect pests . . . . . . . . . . . . . . . . . 11

Diseases . . . . . . . . . . . . . . . . . . . 20

Physiological disorders . . . . . . . . . . . . 21

Problem solving . . . . . . . . . . . . . . . 22

Related publications . . . . . . . . . . . . . 24

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Apples

THE APPLE TREECultivated apple trees generally consist of twocomponents—the rootstock, the below-groundpart that controls tree size, and the scion, theabove-ground part that produces fruit. These twoparts are joined by grafting and are equallyimportant.

Apple flowers and fruit are always produced atthe end of branches. If a fruiting branch continuesto elongate, it is from a side (or bourse) shoot.Apple trees may be spur types where fruit areborne on short shoots called spurs, standardtypes where fruit are borne on longer shoots, orintermediates. Spur-type trees are about 25%smaller than standard types.

Apples have two types of buds—vegetative andmixed. Vegetative buds produce only leaves andshoots, while mixed buds produce both leafyshoots and flowers. Each flower bud will producefive flowers. The first to open is the terminal orking flower. The side flowers open later, usuallywithin 48 hours of the king flower. The kingflower produces the largest fruit.

Apples are the most widely planted tree fruit inWisconsin. Apples occur in a wide variety of colors, sizes, flavors, andtextures and can be used in many different ways. Trees range in size fromvery small “super dwarfs” to large standard trees. Besides providing

fruit, apples can be a pleasing addition to the home landscape.

Before purchasing and planting apple trees, consider whether you have thespace, time, and expertise needed to grow and care for them. This bulletin

outlines the basics of apple production. For more information, contact your county Extension office.

Scaffoldbranches

FIGURE 1. Important parts of a young appletree. The graft union shows where the rootstockand the scion were joined.

Graft union

Rootstock

Centralleader

Scion(desired cultivar)

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Apple flowers are self-unfruitful. That is, pollenproduced by a flower from one cultivar cannotpollinate flowers from the same cultivar. Pollenmust come from flowers from a different cultivar.Insects, usually honey bees, carry pollen fromone tree to another.

The trunk and branches of an apple tree need tobe trained and pruned to support the weight offruit. Typically, apple trees are pruned to leave amain trunk (central leader) and numerous sidebranches (scaffolds). Selecting scaffold limbs withwide angles from the trunk gives the branchesmaximum strength.

Training apple trees does more than strengthenlimbs, it also improves fruit quality and produc-tion by ensuring that all leaves receive sunlight.Leaves require sunlight to produce carbohy-drates needed for fruit production and treegrowth. Leaves that grow in the shade cannotproduce the needed sugars for quality fruit.

The root system of apple trees is shallow andwell branched. The roots have roughly the samehorizontal spread as the branches. Most of theactive roots are found in the top 12 inches of soilwhere there is adequate moisture, oxygen, andnutrients. Roots do not tolerate wet or poorlyaerated soils. Under these conditions, trunkcrown rot and winter injury are more likely.

SITE SELECTION ANDPREPARATIONOnce a fruit tree is planted it is not easy to moveit to a more suitable location. Therefore, it is desir-able to establish the planting in a well-prepared,suitable site. Site selection and soil preparationshould begin the season before planting. Planningahead allows time to adjust the soil pH, controlperennial weeds, and amend the soil.

The first consideration when selecting a site isdetermining how much space each tree willrequire. Smaller sized (dwarf) apple trees requirethe least amount of space. Dwarf apple treesrequire about 75–100 square feet each and grow

8–10 feet tall. Semi-dwarfs require 125–200square feet each and grow to 10–20 feet. Standardtrees take 300–400 square feet or more and maybe over 30 feet tall.

The ideal site for apple trees is on land with agentle slope so that cold air can settle into adja-cent lower areas. The bottoms of valleys are“frost pockets” and may be several degreescolder than nearby hillsides. Hilltops are unde-sirable as they may be very windy. Apples growbest in fertile sandy loam soils, though they willgrow in all but the rockiest or heaviest clay soils.The soil must have good internal water drainage,as apple trees will not grow with “wet feet.” Thesoil should be slightly acidic to neutral, with apH between 6 and 7. Apple trees require full sunat least three-fourths of the day. Shady locationsare not suitable for apple trees.

Once a suitable site has been located, begin soilpreparation. Control perennial weeds either bytillage or by using non-residual herbicides. Takea soil test of the location to a depth of 6 inches.Follow soil test recommendations to adjust thesoil pH: add lime if the soil is too acidic; add sul-fur if the soil is too alkaline. To improve soil tilth,aeration, and water-holding capacity, addorganic matter such as manure, leaves, or com-post. For information on how to sample soil andwhere to send samples for testing, see Extensionpublication Sampling Lawn and Garden Soils forSoil Testing (A2166).

CULTIVAR SELECTIONMany apple cultivars grow well in Wisconsin.When choosing a cultivar, consider intended use(fresh eating, baking, processing), flavor, color,and texture. In addition, the cultivar must bewinter hardy in your area and must ripen bymid-October. Rome Beauty and Jonathan are nottypically grown in Wisconsin because they can’tsurvive Wisconsin’s cold winters. Fuji andGranny Smith require about 180 days betweenbloom and harvest and will not fully mature inWisconsin.

Another factor to consider is disease resistance.Some apple cultivars are resistant to apple scab,the most serious disease problem of apples inWisconsin. Such trees will not have to be sprayedwith fungicides to control the disease and arehighly recommended for home gardens inWisconsin. More information on cultivar selec-tion can be found in Extension publicationsApple Cultivars for Wisconsin (A2105), Home FruitCultivars for Northern Wisconsin (A2488), andHome Fruit Cultivars for Southern Wisconsin (A2582).

Since apple trees are self-unfruitful, there mustbe a second apple cultivar planted close by toprovide pollen for good fruit set. Many floweringcrabapples also can be adequate pollen sourcesfor fruit set in apples. You should assure that thetwo cultivars bloom at the same time so they canprovide pollen to each other. Some apple culti-vars are triploid (have three sets of each chromo-some rather than the normal two sets) and do notproduce viable pollen. Examples of triploidapples are Jonagold, Gravenstein, Rhode IslandGreening, Winesap, and Mutsu (Crispin). If youplant a triploid apple, a second cultivar not inthis group must be planted to provide adequatepollen. Most suburban residential areas have suf-ficient apple and crabapple trees to provide ade-quate pollination without planting two trees.Pollinizer trees should be within 200 yards ofeach other.

ROOTSTOCK SELECTIONApple trees available at commercial nurseriesconsist of two parts: a rootstock (the below-ground portion) and a scion (the desirable com-mercial cultivar). Such trees are made by graftingor budding a desirable scion to a rootstock withdesirable characteristics.

Rootstocks control tree size in apples. Trees ondwarfing rootstocks such as (Malling) M.9 andM.26 are best for home gardens. It is best to ordertrees from nurseries or garden centers that allowyou to select the rootstock. Small trees take upless space, are easier to spray for pest control,

and are easier to prune. Most operations can bedone from the ground, eliminating the need forladders. Dwarf apple trees bear fruit earlier; youcan expect a few fruit in the third year afterplanting dwarf trees. Standard trees won’t bearfruit for 5–7 years after planting. Additionally,planting several dwarf apple trees will yieldmore fruit over a longer season than one largestandard tree. For more information on applerootstocks, see Extension publication Rootstocksfor Fruit Trees in Wisconsin (A3561).

PLANTINGApple trees must be planted correctly. Failure todo so may mean losing the dwarfing characteris-tics of the rootstock. The procedure for plantingbare-root and potted trees is similar.

Bare-root. If trees arrive from the nurserybefore they can be planted in your area, keepthem in a cool place but don’t allow them tofreeze. Open the container and make sure theroots are still moist. If not, add a small amount ofwater to moisten the roots, but don’t saturatethem. You may soak the tree roots in a bucket ofwater for 4–8 hours before planting.

Potted. Potted trees may be kept for 2–3 weeksin the container. Potted trees will need regularwatering, but don’t overwater. The soil shoulddry slightly between waterings. Remove the treefrom the pot before planting and spread theroots. If the roots circle the inside of the con-tainer, make several vertical cuts through theroots and spread them out away from the trunk.

When you are ready to plant the tree, dig a holelarge enough to accommodate the roots withoutbending or cutting them. If one root is very longit can be shortened, but in general don’t prunethe roots. The hole should be deep enough so theentire root system will be in the ground with thegraft union 2–3 inches above the final soil level.The scion must not be in contact with soil or itmay produce roots and the dwarfing influence ofthe rootstock will be lost! Don’t add fertilizer orfresh manure to the hole. Fill using the soil

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Apples

removed from the hole and gently pack it in withyour foot to ensure good contact of the soil withthe roots. Water the tree immediately.

Stake trees on dwarfing rootstocks immediatelyafter planting. Suitable staking materials include3⁄4-inch metal electrical conduit, pressure-treated2 x 2 lumber or a 2-inch-diameter round stake.Stakes should be 10 feet long. Place the stake 3–4 inches from the tree and drive it 2 feet into theground. Using light rope, tape, or fabric strips, tiethe tree loosely to the stake in a figure 8 patternwhere the tie crosses between the stake and thetree. This will hold the tree away from the stakeallowing branches to grow on the stake-side ofthe tree. Tape may need to be replaced periodi-cally. The stake should be left in place for the lifeof the tree.

IrrigationYoung trees benefit from regular watering.During the first year an apple tree should receive1–2 inches (3–5 gallons) of water weekly. As treesget older their roots explore a larger volume ofsoil and irrigation becomes less critical. Don’twait for trees to wilt or show other signs of watershortage before watering. Regular wateringthroughout the season from planting and budbreak to leaf-fall will be most beneficial.

MINERAL NUTRITIONLike all plants, apple trees require some essentialmineral elements in order to grow. Have yourgarden soil tested the year before planting appletrees and till in all recommended nutrients.Micronutrients such as zinc, boron, and copperare not required in great amounts and fertilizingwith these nutrients is usually not needed inWisconsin.

Nutrients can be applied as liquids, granules, ormanures. Granular fertilizer is usually the leastexpensive form. Incorporate granular fertilizer bytilling the soil or watering within 24 hours ofapplications to get the fertilizer into the soil.Liquids can be applied with a hose-end applica-

tor or watering can. Dilute liquid fertilizersaccording to package directions. Manures aretypically low in mineral content and should beaged before shallowly incorporating them.

Several weeks after planting, a light applicationof a nitrogen-containing fertilizer can be made.Apply the fertilizer evenly around the drip lineof the tree (the ground area under the canopy).The rule of thumb is to apply 1 ounce of actualnitrogen to each tree per year of tree age, but notto exceed 1⁄2 pound of actual nitrogen per treeannually. Be sure to include any fertilizer appliedto lawns under trees in the total annual amount.

To calculate the amount of fertilizer to apply,divide the actual nitrogen needed by the percent-age of nitrogen in the fertilizer. For example, a3-year-old tree should receive 3 ounces of actualnitrogen. To calculate how much ammonium sul-fate (which is 21% nitrogen) to apply, divide3 ounces by 0.21 for a total application of14 ounces of fertilizer.

You may need to adjust the standard nitrogenapplication based on the tree’s growth. Shoots onyoung apple trees typically grow 15–20 incheseach year while shoots on bearing trees grow 8–12 inches annually. If growth is less than normal,apply 25% more fertilizer. If growth is more thannormal, don’t apply any nitrogen for a year.

WEED MANAGEMENTManagement of the soil around the trunk of thetree affects tree performance. Do not allow grassor other vegetation to grow within 18 inches ofthe trunk of the tree. A vegetation-free area of 2–3feet is even better. Vegetation competes with treesfor water and nutrients. Grass growing up to treetrunks also makes it difficult to mow withoutdamaging the tree trunk.

Prevent weed growth around tree trunks bymulching, cultivating, or applying herbicides.Cultivate shallowly (no deeper than 1–2 inches)to avoid damaging tree roots. Organic and inor-ganic mulches will prevent weed growth. Mulch

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Apples

is ideal because it prevents weed growth andconserves soil moisture. Apply 3–4 inches of anorganic mulch such as shredded bark, bark chips,or wood chips. Spread the mulch in a donut fash-ion around tree trunks. Avoid heaping mulcharound tree trunks. This can lead to fungal rotson the trunk and attract rodents that gnaw onthe bark.

Glyphosate (Roundup or Kleenup) is the easiestherbicide to use to prevent weed growth aroundtree trunks. For young trees, wrap the trunk withaluminum foil or plastic wrap before applyingherbicide. Apply glyphosate according to labeldirections and avoid getting spray on the trunkor leaves (or you!). Spray only on calm days.

TRAINING AND PRUNINGAnnual training and pruning is essential to theproduction of high-quality apples and to main-tain the health and longevity of trees. Propertraining and pruning allows light throughout thetree canopy and is required for producing qualityfruit. Pruning is always vegetatively invigoratingnear the cuts and may delay fruiting.

Remove all dead or broken branches annually,also suckers, water sprouts, and branches form-ing narrow angles that cannot be spread. Remove

the weakest of crossing or closely parallel-grow-ing branches. Remove downward-growingbranches and spurs. Thin out dense areas, partic-ularly in the top of the tree. Thinning cuts(removing an entire branch to its point of origin)are better than heading cuts (removing a portionof a branch) in making trees less dense.

S tudies have shown that the angle a

branch grows at determines the amount of

fruit it can produce. Branches that grow

straight up will produce mostly vegetative

growth and very little fruit. By contrast,

branches that grow straight out from the

tree are very fruitful, but will produce little

new vegetative growth. The ideal limb posi-

tion is about 30° above horizontal, creating

a 60° crotch angle. This maximizes fruit pro-

duction while still promoting growth of new

wood for future fruiting. The easiest time to

adjust limb position is when branches are

only 3–6 inches long with very soft wood.

PROMOTING FRUITFULNESS

Adapted from Oberhofer, H. 1990.Pruning the Slender Spindle. BC Ministry of

Agriculture and Fisheries, Victoria, BC Canada

60˚

30˚

best positionannualgrowth

FIGURE 2.Spread organicmulch in a donutshape around thebase of the tree.Don’t heap mulchagainst the trunkbecause this cancontribute to fun-gal rots or attractrodents.

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Positioning weights on a branch.Avoid placing the weight so far from the trunkthat the branch bends down in an arc; toomuch bend may mean the crotch angle iswider than you’d intended. The position mayneed to be adjusted periodically.

L IMB POSITIONING TECHNIQUES

Toothpick and clothespin spreaders.Use when branches are 3–6 inches long. Ifusing toothpicks, gently push them into thesoft bark of the limb and trunk to hold themin place.

Wooden spreader. For use on brancheslonger than 6 inches. Notch the ends or, forlarger stock, drive small nails into each endof the spreader, then cut off the heads of thenails using heavy pliers to create a sharp sur-face that will hold in the tender bark.

Various methods of tying and weighting.You can use twine, string, fiberglass tape, long rub-ber bands, or other material. Take care to not tiematerial tightly around branches. Use in late Junewhen young branches are at least 8 inches long.

60°

too close to trunk

just right

weightstring

rubber band

too far from trunk

Do not leave stubs when pruning. Make cutsclose to the trunk but do not remove the collar.These cuts will heal most quickly. Do not usepruning-wound paints or coatings as they keepthe wound moist, allowing diseases and insectsto invade the tree. It is best to allow the wood todry naturally. The tree will produce growth thatwill eventually cover the cut.

The best time to do major pruning is in latespring while the trees are still dormant (Marchand April). Prune between late July and earlyAugust to remove water sprouts and to allowlight into thick canopies. Do not prune after earlyAugust as it can delay dormancy and predisposetrees to more winter injury.

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Apples

Training young treesThe objective in training a young tree is todevelop a structure that will provide a strongframework to support fruit production. The topof the tree should be smaller and narrower thanthe bottom of the tree. This shape prevents thetop of the tree from shading the bottom of thetree. The central leader system (illustrated below)produces a vertical central leader or main stemand strong, properly spaced scaffold limbs. Thissystem is easy to prune and provides optimumproduction potential.

Over the years, you will train two to three tiersof scaffold branches. These branches will formthe central framework of the tree and shouldgrow at a wide angle from the leader.

At planting. If you plant an unbranched whiptree, cut off the top leaving the tree 30–45 inchestall. Side branches will grow from the whip thefirst year. New branches will grow just belowthis cut. You control the location (height) of thenew limbs by the height of the cut. If you’ve pur-chased branched trees, remove only broken,damaged, or poorly positioned limbs.

First year spring. Choose four or five goodbranches for the lowest tier of scaffolds. The low-est scaffold limb should be at least 24 inchesabove ground and can be as high as 36 inches ina landscape where flowers or bushes under thetrees are desired. Limbs growing closer to theground make it difficult to work around the tree.Select well-spaced branches growing withinabout 18 inches of the lowest branch that aregrowing neither exactly opposite nor directlyabove one another. Remove weak or poorly posi-tioned limbs that will not become scaffolds.

Second and third year spring. After two orthree years, select a second tier of scaffold limbs.Again, choose or create branches with widecrotch angles. The lowest branch of the secondtier should be at least 24 inches above the topbranch of the lower tier. This 24-inch gap allowslight to penetrate into the canopy and to strikethe lower tier of branches. The upper branchesmust be kept shorter than the lower branches to

At planting First year spring

Graft union should be2–3 inches above soil line.

24–36"

30–45"

first tier

keep them from being shaded. This will create a“Christmas tree” shape. For dwarf trees, two tierswill be sufficient; for semi-dwarf trees, repeat theprocess to create a third set of scaffolds near thetop of the tree.

Yearly maintenance. The central leader mustremain the tallest part of the tree. The highestpoint in the tree is dominant and most vigorous.If a side branch is becoming nearly as tall as theleader, bend it lower (see limb positioning) orprune it back into 2-year-old or older wood.

Once the central leader reaches the height youwant (usually 8–10 feet high for dwarf or 12–16feet high for semi-dwarf) you can adjust thevigor in one of two ways (figure 3). Take the top,supple part of the leader, bend it in an arc and tieit to the support post or the stronger part of the

tree. As new branchesbegin to grow on the arc,remove the ties andallow the leader to returnto the vertical position.Alternatively, cut off the leader just above a weakside branch. Both techniques reduce the vigor ofthe top of the central leader. To maintain treeheight, follow one of these techniques every yearfor the life of the tree.

9Second year spring Third year spring

24" gap

24" gap

FIGURE 3. Techniquesfor maintaining trees at aspecific height.

third tier

second tier

Remove all dead and broken branches annually,as well as suckers, water sprouts, and branchesforming narrow angles. By the fifth year, treesshould be well established with two tiers of scaf-folds. Spurs should be developing throughoutthe tree to provide annual fruiting.

Pruning bearing treesThe objective of pruning bearing trees is to main-tain maximum production of high quality fruiton a continuing basis. Properly trained treesrequire little pruning but must still be prunedannually. Limit pruning of bearing apple trees toremoval of weak, unproductive branches toimprove light penetration and distribution,reduce tree height, and improve spray coverage.

As trees grow older, you may need to make morethinning cuts. Don’t let the upper branches growlonger than the lower branches. Long upperbranches shade lower branches and reduce pro-ductivity. If necessary, prune upper branches into2-year-old or older wood to keep them shorterthan lower branches. Thin out weak, unproduc-tive branches, and keep the tree “open” for goodlight penetration. In the top of the tree, branchescan be cut back to the trunk leaving a short stub(about 1⁄2-inch long) on the bottom of the cut(figure 4). A new branch will often grow from thebase of the stub.

If an older tree is too tall for convenient sprayingand harvesting, more drastic steps must be taken.To lower the height of a tree, completely removeone or two of the tallest growing limbs. Make thecut where the limb joins the trunk. When youprune drastically, you must greatly reduce otherpruning in the tree that year. Over-pruning willstimulate too much growth and lower fruit pro-duction. Spread out extensive renovation prun-ing over 2–3 years.

HARVESTApples ripen over about a 3-month period in thefall ranging from early August to late October.Harvest apples before they are fully ripe, butafter they are mature. Maturing apples undergochanges in skin color, seed color, flavor, and firm-ness. As apples mature, they lose the brightgreen skin color of immature apples. Red applesbegin to turn red on the exposed side of the fruit;yellow apples first turn pale green then yellow;and green apples change from bright green topale green. Seeds change from cream to tan todark brown. Immature apples have a verystarchy taste and little apple aroma. As the fruitmatures, the starch changes to sugar and thearoma and flavor develop. Immature apples arehard to the touch and are very hard and crispwhen cut. Mature fruit should be firm but nothard. Different apple cultivars vary in their firm-ness at maturity.

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1⁄2-inchstub

FIGURE 4. Pruning to promote new growth.

To harvest fruit, hold the apple in the palm ofyour hand and twist it slightly while pulling.Gripping apples using only your fingertips willbruise the fruit. Avoid pulling spurs or branchesfrom the tree—these structures contain fruit budsfor next year’s crop. Gently place fruit into a pick-ing bag or basket. Never throw or drop fruit asthis will bruise the fruit. Empty the container care-fully into boxes or bins to prevent bruising fruit.

STORAGEOnce harvested, many apples will keep for sev-eral months if stored properly. Summer apples,which ripen before Labor Day, generally do notstore well and can be kept only a few days to 2weeks. Fall- or winter-ripening apples, whichripen in September and October, will store wellfor 1–5 months. If you plan to store the apples,harvest them before the peak of maturity whilethey are still firm. Discard or use any blemished,diseased, or damaged fruit. Store only the bestfruit. Overripe or bruised apples will not onlystore poorly, but the ethylene gas they producewill shorten the storage life of sound fruit.

Cool apples promptly and keep them constantlycold. For short-term storage, refrigerate at tem-peratures below 40°F. For longer storage, temper-atures of 32°–34°F and high humidity arerequired. Don’t allow fruit to freeze. Keepingfruit in plastic bags with small holes in the bagswill help avoid water loss and shriveling. Checkthe fruit occasionally and remove soft or dam-aged fruit.

INSECT PESTSOver 50 types of insects attack apple trees,foliage, or fruit in Wisconsin. Of these, about adozen are fairly common, but not all occur atdamaging levels every year or in every location.

There are two approaches to apple insect man-agement: a preventive approach where insecti-cides are applied routinely regardless of actualinsect damage, and a curative approach wherecontrols are applied only when pests are presentand capable of causing significant damage.

The preventive approach is used by apple grow-ers who are unable to do routine pest monitoringor who are uncomfortable trying to identify pestsand damage.

A minimal preventive program uses three to fourinsecticide sprays per year, timed at petal fall,2 weeks after the first spray, mid-July, and earlyAugust. This spray program usually protects asubstantial proportion of fruit. Where the bestpossible fruit quality is desired, or where insectnumbers are high, a more thorough insecticideprogram may be necessary, with applications at10- to 14-day intervals starting at petal fall andextending through August or early September.

The best approach to insect pest management isthe curative approach. This involves learning torecognize common pests and the types of injurycaused, monitoring pest activity routinely(weekly throughout the growing season), andapplying insecticides only when necessary.

The chart (table 1) will help you determine whento monitor for the most serious insect pests. Itsummarizes when insects are likely to be present,and the best times to apply controls. Use thechart together with the detailed insect informa-tion to know when controls are appropriate.

Several methods can be used to monitor insectactivity, including sticky traps, pheromone traps,and visual inspection. Not all methods work onall insects. Specific monitoring information isgiven for each pest.

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Pheromone traps are sticky traps with a synthe-sized attractant that mimics the natural odor orpheromone produced by female moths forattracting males for mating. The traps catchmales and help identify when mating occurs.Traps can be purchased at better garden centersand through mail-order catalogs. For best results,follow manufacturer’s directions.

Do not use insecticides during the blossomperiod. Apples are pollinated by honey bees andother insects. Broad-spectrum insecticidesapplied during flowering will kill these beneficialinsects and interfere with pollination.

The following descriptions are of the most seri-ous apple insects in Wisconsin. More thoroughand inclusive descriptions can be found inExtension publication Common Tree Fruit Pests(NCR063). For additional information on specificpests and pesticides, see also the list of publica-tions at the end of this book.

Fruit-damaging insectsThe most serious insect pests of apples are thosethat directly damage the fruit. These includeapple maggot (railroad worm), various types ofcaterpillars such as leafrollers, fruitworms, andcodling moth, plum curculio, and rosy appleaphid.

Apple maggot(railroad worm)

The adult apple maggot is atype of fly that lays eggs infruit. The larvae tunnelthroughout the fruit, causing it todeteriorate and drop. Apple maggot is a summerpest, causing injury from early July until harvest.If uncontrolled, it is the most serious insect pestof apples in Wisconsin.

Type of damage. The adult apple maggot flylays eggs under the skin of apple fruit. Severaleggs may be laid in a single fruit. The fruitdecomposes around the site of the sting, causinga small, darkened depression. The eggs hatch

into tiny, transparent larvae that tunnel throughthe fruit, leaving slender, brown trails. Fruit startto deteriorate and eventually fall from the tree.

Apple maggots also attack pear, cherry, andplum, as well as native hawthorn.

Description. The apple maggot fly is abouttwo-thirds the size of a common house fly. Itsbody and wings are marked with black andwhite bands and spots. The larvae are headless,legless cream-colored maggots about 1⁄ 3-inch longwhen fully grown. Young larvae are very tinyand virtually transparent, making them difficultto find within apple fruit, even with the aid of amicroscope.

Monitoring. Hang sticky traps during the lastweek in June and continue trapping until the firstfrost. There are two types of apple maggot traps:yellow sticky boards and red sticky spheres.Yellow traps are less efficient, but pick up insectsbefore they start to lay eggs. The red sphere trapis efficient for monitoring reproductively matureflies. An “apple volatile” lure, available for hang-ing with the red sphere, greatly increases theattractancy of this type of trap.

Apple maggot traps are not as selective aspheromone traps; many different types of insectscan be caught on apple maggot traps. For thisreason, it is important to be able to recognize theapple maggot fly and differentiate it from other,similar insects. Two types of cherry fruit fliesoccur in Wisconsin and are easily mistaken for theapple maggot fly. They can be distinguished basedon differences in wing pattern (see illustration).

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Apples

1⁄4"

Apple maggot

Black cherry fruit fly

Cherry fruit fly

Wing banding pattern of fruit flies

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Fruit-damaging insects

Apple maggot Hang sticky traps last week in June.Control is most critical July throughAugust.

Caterpillars

Fruittree leafroller Hang pheromone traps early June. Criticalmonitoring time during bloom. Spray onceat petal fall.

Redbanded leafroller Hang pheromone traps mid-April and mid-July. Spray once at petal fall and for secondgeneration if necessary.

Green fruitworm Spray once before blossom or at petal fall.

Codling moth Hang pheromone traps early May. Applyfirst spray about 1 week after petal fall.

Plum curculio Apply first spray at petal fall. Check fruitfor egg-laying damage in spring, feedingdamage in late summer.

Rosy apple aphid Control as needed starting at petal fall.

Plant-damaging insectsCaterpillars Several species can damage fruit and

foliage throughout season. Treat as needed.

Japanese beetles Apply sprays as needed or use floating rowcovers as soon as adults appear.

Scale insects Monitor fruit, foliage, and stemsthroughout year. Spray before budbreak orduring crawler stage.

Spider mites Most damage occurs mid-June throughAugust. Apply dormant spray, treat asneeded throughout season.

Spotted tentiform leafminer Hang pheromone traps early April. Countmines mid-June, early August, and earlyOctober.

March

April

May

June

July

August

Septem

ber

October

Comments

TABLE 1. Approximate dates for monitoring and controlling insectpests. Dates will vary depending on weather and location in state.Do not apply insecticides during blossom period.

Monitor adult insects

Monitor larvae and/or damage

Control periods

Check fruit for damage beginning mid-July andcontinuing until harvest. Infested fruit can bedetected by the shrunken, discolored dimples.When cut into, the normally white flesh will becrossed with the pale brown trails of the youngmaggots.

Prevention and control. Use, destroy, or buryinfested fruit as soon as they fall from the tree.Do not compost these fruit because larvae maysurvive.

Apple maggots can be controlled by trapping.Use the round red spheres along with the com-mercial apple volatile bait. Research shows thatone trap per 100 apples will catch most flies andwill minimize fruit injury. In larger plantings,place a ring of traps around the planting byhanging traps every 50 feet on the outside of theperimeter trees.

Apple maggots can be controlled with insecti-cides. In lightly infested areas, spray in early Julyand repeat once or twice at 2- to 3-week inter-vals. Reduce the time between sprays in heavilyinfested areas. Sprays can be timed by usingtraps to monitor for adult fly activity; spraywhen the first flies are caught, and again aftersubsequent catches, but no more frequently thanevery 2 weeks.

Caterpillars—leafrollers, fruitworms,and others

The larvae (caterpillars or “worms”) of severaltypes of moths feed on apple foliage and fruit.Leafrollers (especially redbanded leafrollers andfruittree leafrollers) and green fruitworms are themost common, but others include inchworms,cankerworms, and webworms. Most of these areearly-season pests, causing damage shortly afterthe blossom period, although a few cause dam-age in midsummer.

Type of damage. The larvae feed on bothleaves and fruit. Young larvae feed on leavesduring the blossom period, causing minimaldamage to the tree. Leafrollers use silken web-bing to roll leaves or tie two or more leavestogether, creating a refuge in which they live andfeed. Leaves are often tied around clusters ofyoung developing fruit, and the larvae feed onthe fruit surface, causing superficial smooth orcorky brown scars. Such damage caused early infruit development heals naturally, and, althoughthe fruit is scarred, the flesh is usable and doesnot rot. In contrast, green fruitworms do not tieleaves together and they feed deeper into theyoung fruit. Feeding damage from green fruit-worms may cause the fruit to abort and dropfrom the tree. More mature fruit in summer arenot able to heal feeding wounds, and usually fallfrom the tree and rot. Leafrollers, green fruit-worms, and similar caterpillars do not tunnelinto fruit, but feed only from the surface.

Leafrollers, green fruitworms, and similar cater-pillars feed on many types of broadleaf trees andshrubs, often in wooded areas adjacent to whereapples are planted. Some types also readily feedon other cultivated fruit plants, including pear,apricot, plum, and even berries.

Description. Leafroller larvae are pale yellowto pale brown, and have a yellowish, brown, orblack head, depending on species. They growfrom 1⁄8-inch long at hatching to about 3⁄4-inchlong. Green fruitworms are much larger androbust, growing to over 1-inch long. They aregreen and may have small white spots or palelines which run the length of the body.

Monitoring. Check during the blossom periodfor signs of larval feeding, which may appear astattered leaves or leaves with holes chewed inthem. Also check for leaves that appear stucktogether; carefully separate these to determine ifleafroller larvae can be found.

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Apples

1⁄2–3⁄4"

Pheromone traps are available for redbanded andfruittree leafrollers. These will help determineflight periods and therefore when eggs are beinglaid. Trap for redbanded leafroller mid-Aprilthrough mid-June and again from mid-Julythrough August. Trap for fruittree leafrolleradults from mid-June through mid-July.

Prevention and control. Insect populationsvary from year to year, in part depending onnumbers in nearby forests, wood lots, or aban-doned fruit trees. In some years they may beessentially nonexistent, whereas in other years,severe defoliation or fruit injury may occur if thetrees are not protected.

Insecticide sprays applied at petal fall (the veryend of bloom, when 75% of the flowers havefallen) will control most types of caterpillars.Traditional insecticides may be used. Also, micro-bial insecticides containing the active ingredientBacillus thuringiensis will usually provide satisfac-tory control as long as they are applied when thelarvae are very young.

Codling moth

Codling moth lar-vae are caterpillarsthat feed entirelywithin the fruit.This is one of the insect pests that cause“wormy” apples. Codling moth is not native toNorth America; its original home is Asia. It nowoccurs throughout the world, and is consideredto be the single most important insect pest ofapples worldwide.

Type of damage. Tiny codling moth larvaebore into the fruit and tunnel to the core. Theyfeed on the developing seeds and adjacent tis-sues. Their feeding leaves black residues and rotsthe center of the fruit. One or more noticeabletunnels lead directly to the outside, and insectwaste (frass) can pile up on the skin of the fruit.Damaged fruit fall from the tree and decompose.If harvested, damaged fruit rot rapidly, even ifrefrigerated.

Description. Codling moth larvae are less than1⁄8-inch long when they first hatch, eventuallygrowing to over 1⁄2 inch. Older larvae have abrown or black head and a body that is creamywhite to slightly pinkish in color. Larvae havethree pairs of conspicuous legs near the head anda series of fleshy legs along the body. Adultcodling moths have wings with slender bands ofalternating gray and tan; the tips of the frontwings are shiny golden-brown. The wings areheld tent-like over the body.

Monitoring. Pheromone traps are available forcodling moth. Hang traps at the beginning ofbloom and maintain them through mid-August.Replace the lures in early July in preparation forthe second flight of adult moths. Check trapsweekly.

Damage by larvae is easily observed because ofthe piles of frass on the outside of the fruit. Forpositive confirmation, cut open a suspect appleand check for feeding injury and rot in the core.

Prevention and control. If possible, eliminatewild hosts (apple, pear, hawthorn) growingwithin 100 yards of cultivated apple trees.Remove windfall fruit, which are usually insectinfested. If these fruit are not utilized, bury atleast 2 feet deep. Larvae can complete develop-ment if fruit are merely composted. Sprayingonce about 1 week after petal fall and againabout 10 days later gives the most control. Ifnumerous wild host plants grow nearby, appletrees will need an additional one to two sprays tocontrol the summer generation. Time the spraysbased on noticeable increases in pheromone trapcatches, usually from mid-July to early August.Microbial insecticides containing Bacillusthuringiensis are not particularly effective againstthis insect.

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5⁄16"

Plum curculio

Plum curculio is a nativespecies of weevil, a type ofbeetle. As its name suggests,its preferred host is plumbut it attacks other stonefruits as well as apple andpear. Plum curculio is com-

mon throughout Wisconsin and is one of themost damaging apple insects.

Type of damage. Plum curculios damageapples in three ways: egg laying, larvae feedingwithin the fruit, and adults feeding at the fruitsurface. The adult female scars the fruit surfaceat egg laying by cutting small crescent-shapedflaps in the skin of young fruit. This damageoccurs when the fruit are smaller than 11⁄2 inchesin diameter. As the fruit grows, it becomes verymisshapen, with lumps and dimples. Many eggsand young larvae do not survive in the hard tis-sue of young apples. Ifthey do, the larvae tun-nel through the fruit,causing considerabledeterioration and even-tual fruit drop. Adultsfeed on the fruit surface,causing small, shallowirregular holes. The sur-rounding areas decay and rot.

Description. Adult weevils are less than 1⁄4-inchlong and are gray-brown to dark brown. Theplum curculio has three pairs of bumps on theback, and a long curved snout on the front of thehead. The larvae are pale and grub-like, with adistinct pale brown head but no legs. Fullygrown larvae are about 1⁄4-inch long.

Monitoring. Monitor for adult weevils frommid-April through mid-June and again from lateJuly through mid-September. To monitor, spreada white sheet beneath a tree, then sharply tap thebranches with a stick. Adults will fall to thesheet, pretending to be dead. Check fruit for 4weeks beginning shortly after petal fall; look forthe characteristic crescent-shaped scars.

Prevention and control. Collect and burywindfalls as soon as they fall. As the weevils caneasily tunnel through soil, bury fruit at least 2–3feet deep. If possible, remove vegetation fromfence rows and eliminate other sites where bee-tles may overwinter. Chickens readily feed onmigrating beetles and may provide some benefit.Do not allow chickens to forage in areas treatedwith pesticides or where there may be pesticidedrift or runoff. Appropriate insecticides appliedat petal fall and 10–14 days later will provideexcellent control.

Rosy apple aphid

There are several types ofaphids that feed on appletrees. Of these, rosy appleaphid is the only type thatinjures the fruit.

Type of damage. Aphids feed by sucking plantsap from leaves and small succulent stems.During feeding, they inject saliva into the plantto aid in feeding and digestion. Aphid saliva isoften toxic to the plant. When rosy apple aphidsfeed near young fruit, the injected saliva ismoved by the plant into the fruit, resulting insmall, hard, misshapen apples.

Description. These aphids are about 1⁄8-inchlong and are generally found in large colonies.They vary in color from a pale rose to dark pur-ple and are partially covered by a whitish, dustymaterial. Occasionally, black, winged individualscan be seen in the colony.

Monitoring. Check leaves near flower clustersfrom the end of the blossom period through June.Infested leaves will be curled, with the aphidsfeeding on the lower leaf surfaces. The clusters ofsmall aphids are easily seen. Do not confuse rosyapple aphid with other aphids which are not asdamaging.

Prevention and control. Elimination ofbroadleaf weeds from the vicinity of the appletrees may help reduce local populations byrequiring the winged aphids to fly further to findtheir required alternate summer host plant, nar-row-leafed plantain.

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Apples

1⁄8"

scars caused byegg laying

1⁄4"

Native natural enemies, such as lady beetles andlacewings help control all aphids attackingapples. Lacewing eggs can be purchased com-mercially and released into the trees during theblossom period to augment native natural ene-mies; we do not recommend purchasing ladybeetles because they disperse too rapidly afterrelease.

An appropriate insecticide applied at petal fallwill control aphids. Insecticidal soap will providesome control if coverage is thorough.

Plant-damaging insectsInsects and mites that feed on foliage or branchesweaken trees. Severe infestations can cause treesto grow poorly, resulting in reduced bloom andfruit set, and small, low-quality fruit. This groupof pests includes aphids, caterpillars, scaleinsects, spider mites, and leafminers.

Aphids

Several types of aphids feed on apple foliage andyoung stems throughout the growing season.Feeding damage often causes newly developingleaves to twist and curl. Other than rosy appleaphid, aphids are generally of minor conse-quence to apple trees. For information on preven-tion and control, see rosy apple aphids.

Caterpillars

Various caterpillar species are important defolia-tors of apple trees. Some feed on fruit as well asleaves. Eastern tent caterpillar and fall webwormare common problems. Both caterpillars are rela-tively large and hairy. Eastern tent caterpillarsspin densely webbed “tents” in early spring,soon after the first leaves have formed. The lar-vae first feed in groups, outside of their tents,and several colonies can completely defoliate atree. They return to their tents when not feeding.Fall webworms produce large loose tents whichsurround the colonies of feeding larvae; there aretwo generations, spring and late summer. For adiscussion of control, see the previous section oncaterpillars in “Fruit-Damaging Insects.”

Japanese beetle

The Japanese beetle is a relativelyrecent invader of Wisconsin. It ismost serious in the southern partof the state, but extends into cen-tral Wisconsin, and will likelycontinue to be an increasing problem.

Type of damage. They feed on many types oftrees and shrubs. The USDA lists apples as one ofthe beetle’s top 10 favorite food plants. Beetlesprefer apple foliage and usually will not feeddirectly on the fruit. Populations can build tovery large numbers, resulting in substantial defo-liation of the trees.

Description. The 1⁄3 inch beetles are reddishbrown and metallic green, with a series of whitetufts of hair around the edge of the wing covers.The larvae are white grubs that feed on plantroots and organic matter in the soil, especiallyunder turfgrass.

Monitoring. Japanese beetles are strong fliersand can invade from considerable distances fromoutside the immediate garden area. Watch forthem from late June through early August.Modest defoliation (10–15%) will not affectmature fruit trees or yield, but higher levels ofdamage will stress trees and reduce crop yieldand quality. Substantial defoliation to youngtrees will delay their establishment.

Prevention and control. Many insecticidesregistered for use on apples will kill Japanesebeetle adults, but others may soon fly in fromadjacent untreated areas. Japanese beetle trapsare available and can catch thousands of beetles,but, because they can attract more beetles thanthey catch, research has shown that the use oftraps can actually increase damage to small gar-dens. If you use traps, they should be placed atleast 50 feet away from plants you wish to pro-tect. If you have just a few small fruit trees, youmay find success using the woven fabric “float-ing row covers” that are available to protect gar-den plants from flying insects.

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Scale insects

Scales are tiny insects that feed by sucking sapfrom branches, leaves, or fruit. During most oftheir lives, scale insects are motionless and cov-ered by a hard waxy coating. The shape and sizeof the coating varies with species. Two scaleinsects occasionally occur on Wisconsin appletrees, San Jose scale and oystershell scale.

Type of damage. Young scale crawlers can set-tle on fruit. Their feeding leaves small (1⁄8–1⁄4 inchin diameter) red halos on green or yellow fruit.In addition to fruit injury, heavy infestations canstress trees and result in die-back of stems andbranches.

Description. San Jose scale is very tiny, onlyabout 1⁄16 inch when fully grown. The covering iscircular, in the shape of a flattened cone. Theyoverwinter as partially grown scales on the tree.They mature and produce young, calledcrawlers, by mid-June. Crawlers seek appropriateplaces to settle and start to feed. A second gener-ation occurs in summer. Because of their tiny sizeand brown color, San Jose scales are difficult tosee on branches or trunk; they are usually firstnoticed when they start to infest fruit. By thistime, the tree is usually heavily infested.

Oystershell scale is less common than San Josescale, but causes similar damage. It is slightlylarger and elongate, in the shape of a musselshell. It overwinters in the egg stage under thescale covering of the mother. Eggs hatch 2–3weeks after apple blossom and crawlers moveabout until they find an appropriate place to set-tle on the stems or branches of the tree; occasion-ally they will settle on young fruit. The scalesgrow slowly throughout the year, and there isonly a single generation per year.

Monitoring. Because of their small size, scaleinsects are often overlooked unless they areabundant. If the characteristic fruit damage isseen, carefully examine the tree trunk andbranches for scale colonies.

Prevention and control. Lime sulfur sprays orsuperior oil applied during dormancy controlsboth types of scale. Crawlers can be controlledwith one to two applications of a conventionalinsecticide, timed 2–4 weeks after petal fall.

Spider mites

Spider mites are very tiny creaturesthat are more closely related to scorpi-ons, spiders, and ticks than they areto insects. There are many differenttypes of spider mites, all of which areplant feeders. Two types, Europeanred mite and twospotted spider mite,commonly attack apples.

Type of damage. Mites suck sap and nutrientsfrom leaves. Their feeding damages leaf surfaces,causes moisture loss, and reduces the plant’scapacity to produce energy for growth and fruit-ing. Damaged leaves first become slightly yellow,then take on a purplish or bronze coloration.

Description. Both species of spider mite arevery tiny, being only about 1⁄50-inch long whenfully grown. Twospotted spider mites are paleyellow, with a large dark spot on either side ofthe body. These mites produce very fine silkenwebbing along the leaf edges and veins, whichbecomes quite noticeable when population num-bers are high. European red mites are dark red-dish brown and do not produce silken webbing.Both types of mites have many generations eachyear and can build to very high levels. Theyreproduce rapidly in warm, dry weather and canaverage more than 100 per leaf.

Monitoring. Because of their very small size, itis helpful to have a 10- or 15-power magnifyingglass when checking for mites. If you see leaf dis-coloration and suspect mites, check 10 randomlyselected leaves from each tree. Most mites will beon the lower leaf surfaces. When smashed

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Apples

size of aperiod.

1⁄50"

1⁄16"

San Jose scale Oystershell scale

1⁄8"

between thumb and forefinger, or against a pieceof white paper, mites will leave a small brownishstain. In early spring, check stems near buds foreggs of European red mites. If eggs are present, adormant spray will control them.

Prevention and control. Natural controls areimportant in regulating spider mites. Heavyrains wash many from leaves, especially onsmaller or well-pruned trees. Many beneficialpredators occur naturally; these include tinypredatory mites as well as lady beetles,lacewings, and other insects that feed on mites.

A dormant superior oil spray applied at the timeof “tight cluster” (when the flower buds firstbecome noticeable) will kill overwintering eggsof European red mite. However, this treatment isineffective against twospotted spider mites,which do not overwinter on the tree.

Insecticidal soap and certain types of conven-tional insecticides will suppress mites during thegrowing season, but may not provide completecontrol. If numbers are high, two applications 5–7days apart may be needed. Commercial growershave access to several miticides that are moreeffective than homeowner products.

Spotted tentiform leafminer

These tiny insects feed within the leaf tissue, leav-ing blister-like leaf mines. Heavy infestationsgreatly reduce the tree’s ability to produce energyfor growth and fruiting. Spotted tentiform leaf-miners are rarely a problem in home orchards,but the mines are noticeable and can be confusedwith other problems such as apple scab disease.

Type of damage. A fully developed leaf mineis about 3⁄4-inch long and 1⁄2-inch wide. It is raisedtent-like on the upper leaf surface, and is speck-led with small silvery spots caused by the larvafeeding within the mine (hence the name spottedtentiform leafminer). The mined portion of theleaf dies, and the tree loses that portion of itsphotosynthetic ability. Heavy infestations causesome cultivars to drop their fruit prematurelyand other cultivars to drop their leaves early.Apple is the primary host of this leafminer,although some crabapple cultivars may be heav-

ily attacked. Other commontypes of leafminers, such as birchleafminer, are unrelated to spottedtentiform leafminer.

Description. The adult is a tiny moth, about3⁄16-inch long, with wings that are banded withgolden brown and white. The larvae are tinycaterpillars, pale yellow in color, and only about1⁄ 5-inch long when fully grown. The pupa isgolden brown and about the same size as thefully grown larva. There are three generationsper year.

Monitoring. Pheromone traps are available formonitoring flight periods. Hang traps just beforebud break and maintain them throughout theyear; change lures according to manufacturer’sinstructions. Monitor for mines starting at petalfall. Each month, count all the mines on 50 ran-domly selected leaves per tree on at least fivetrees in each area of planting, and calculate theaverage number of mines per leaf. An accumu-lated average of at least five mines per leaf atharvest will likely result in sufficient stress toaffect the health of the tree and the size, quality,and storage life of the fruit and may require con-trol the following year.

Prevention and control. The leafminers arenaturally controlled by tiny, stingless wasps whichparasitize and kill the larvae. These wasps areusually highly effective in trees that are not heavilysprayed with broad-spectrum insecticides. If leaf-miners become a serious problem on home appletrees, it usually indicates excessive insecticide use.In these situations, limit insecticides to allow theparasites to build up. Adequate natural controlwill return within one to two growing seasons.

Rake and destroy leaves as soon as they dropin autumn to help reduce the overwinteringpopulation.

Several types of insecticides are available for con-trolling this insect in commercial orchards. Thisinsect has developed resistance to most com-monly used sprays. For home orchards, use anapproved insecticide that has an active ingredientthat is in the synthetic pyrethroid class.

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DISEASESMany disease-causing pathogens (fungi, bacteria,viruses, and nematodes) attack apple trees.Diseases may damage the fruit directly, making itunattractive or inedible. They can also weakenthe tree by injuring the leaves, trunk, andbranches. Damage to the tree reduces productiv-ity and increases susceptibility to winter injury orattack by additional pests. Pathogens must bemanaged to consistently produce high-qualityfruit. For specific chemical and nonchemical rec-ommendations, see Extension publication ApplePest Management for Home Gardeners (A2179) orCommercial Tree Fruit Spray Guide (A3314).

Apple scabApple scab is caused by a fungus and is the mostserious disease affecting apples in Wisconsin. Thedisease damages leaves and fruit and is a prob-lem almost every year. Like many diseases,development of scab is favored by wet weatherespecially during April, May, and early June.

Symptoms of the disease are olive-green to blacklesions on leaves, fruit, or both. Scab lesionsmake the fruit unattractive, misshapen, and inextreme cases cracked and inedible. If the applesare not cracked or severely affected, lesions canbe cut out, leaving the remaining fruit unaffectedand edible.

Tissues are especially susceptible to infectionfrom early spring through June. After that, leavesand fruit can still become infected, but the risk islower. It is important to prevent infections earlyin the season to have “clean” fruit later on.Severe disease can defoliate trees prematurelyand cause complete destruction of fruit.

Prevention and control. The most effectivemethod for controlling scab is to plant scab-resis-tant cultivars. Another practice to help limit scabdevelopment is to remove and destroy (e.g., com-post or burn) apple leaves in the fall. The fungusoverwinters in apple leaves and initial spores inthe spring come from the previous season’sleaves. Fungicides are available for protecting

susceptible cultivars and are most effective ifapplied in the spring before symptoms arenoticed.

Cedar-apple rustCedar-apple rust is also caused by a fungus. Itcauses small, circular, yellow to orange lesions onleaves and fruit. Lesions on fruit usually becomeraised and distorted. Eastern red cedar (Juniperusvirginiana) is the alternate host for the fungus andmust be present for the disease to occur. Air cur-rents can carry spores several hundred yardsbetween cedar and apple trees.

Prevention and control. If possible, removenearby eastern red cedars to help reduce sporelevels. Many of the scab-resistant apple cultivarsare also resistant to cedar-apple rust.Alternatively, fungicide applications duringspring will help control this disease. For moreinformation, see Extension publication Cedar-RustComplex (A2598).

Fire blightFire blight is caused by a bacterium and candevelop quickly following warm, wet weatherduring bloom. Diseased flowers becomeblighted, young branch tips “crook” over, andleaves turn brown to black giving the appearanceof having been burned. Severe disease can killbranches of mature trees and entire young treeswithin a single growing season. The disease isspread by splashing rain droplets and possiblyby insects. Apple cultivars vary in susceptibilityto fire blight. Some rootstocks such as M.9 andM.26 are very susceptible to fire blight.

Prevention and control. Adequate fire blightcontrol is usually obtained with good overallmanagement. Choose resistant cultivars and root-stocks. Do not overfertilize with nitrogen as thisencourages lush growth which is very suscepti-ble to infection. Prune out diseased shoots bycutting at least 12 inches below the lowest visiblesymptoms. Disinfest pruning shears for at least30 seconds in a mixture of 1 part householdbleach plus 9 parts water between each cut to

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Apples

avoid spreading the bacteria. Destroy prunings.During late winter, prune out any affectedbranches that were missed earlier. For moreinformation, see Extension publication Fire Blight(A1616).

Canker diseasesSeveral different fungi can cause cankers onbranches and trunks. If severe, canker diseasescan disfigure or kill trees. Canker pathogensoften infect through wounds created by improperpruning, broken limbs, and “southwest” injury.Southwest injury occurs when trunks expandafter exposure to intense sunlight on winter days,and then quickly contract as the temperature fallsat sunset. Trees that are further weakened duringthe growing season by environmental stressessuch as drought or disease and insect pests areespecially susceptible to canker development.

Prevention and control. See the section ontraining and pruning (page 6). Train properly sotrees are structurally strong and less prone tomechanical damage. Prune properly so woundsheal quickly. Irrigating during dry periods willbolster the tree’s defense mechanisms and reducecanker development. Do not apply nitrogen afterAugust 1 as this will delay winter hardiness.Applying white latex paint to the southwest sideof trunks will help reflect sunlight during winterand minimize cracking due to rapid expansionand contraction.

PHYSIOLOGICAL DISORDERS

Bitter pitBitter pit appears as small brown lesions that aretypically 1⁄4–3⁄ 8 inch in diameter. Lesions may beflush with the surface or sunken. The flesh imme-diately below the skin is browned. Bitter pit is acalcium-related disorder, not a disease. The mostsusceptible trees are those that are growing rap-idly, such as young trees, over-fertilized trees,and heavily pruned trees. Other candidates forbitter pit include large-fruited cultivars anddrought-stressed trees.

There is no “cure” for bitter pit. However, the fol-lowing practices may reduce the severity andincidence of the disorder:

■ Irrigate during dry periods—don’t let the soilaround trees dry out.

■ Don’t over-prune or over-fertilize trees as thisleads to vegetative vigor.

■ On cultivars that have bitter pit every year,consider spraying fruit with calcium chloride.Apply 1 oz/gallon beginning with the firstcover spray (after petal fall). Make three addi-tional treatments at 2-week intervals. Calciumchloride is corrosive, so be sure to clean equip-ment well after spraying.

For more information, see Bittter Pit and Cork Spot(Wisconsin Garden Facts, X1055).

WatercoreWatercore is characterized by watersoaked or“shiny” areas in the flesh of an apple. This disor-der is most common when fall weather is warmand sunny and on later-maturing cultivars.Watercore is thought to occur when sugars aredelivered to the fruit faster than the tissues canuse them. As a result, the excess fluid fills thespaces between the cells.

Apples that have watercore can still be eaten andused for cooking, although affected areas mayhave an off flavor and odor. This fruit will notstore well. Unfortunately, there is no way todetermine from the outside if an apple has water-core. To reduce the incidence, harvest fruit whenmature, but not at the peak of ripeness. For moreinformation, see Extension publication Watercoreof Apple.

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PROBLEM SOLVING

Why apple trees fail to bearThere are many reasons why apple trees fail tobear fruit—spring frosts, poor pollination, age oftrees, too much pruning, and too little training.This section describes the most common prob-lems and how to avoid them.

Cold injury. Perhaps the most common problemis spring frosts. Temperatures below 30°F duringbloom will kill flowers. When spring frosts dam-age flowers, no fruit are formed. Flower budsmay also be killed by extremely cold winter tem-peratures. This is a serious problem on margin-ally hardy cultivars (e.g., Jonathan, GoldenDelicious) and in northern Wisconsin. Coldinjury can often be avoided by choosing goodsites and planting recommended hardy cultivars.

Pollination problems. Poor pollination may bedue to poor weather conditions during flower-ing. If the weather is cold, cloudy, windy, orrainy, bees do not forage well. Insects arerequired for pollinating apple flowers. Withoutinsects to transfer pollen, no fruit results. Appletrees may also fail to bear due to lack of compati-ble pollen. Apples require pollen from anotherapple cultivar to set fruit. Pollinizer trees must bewithin 200 yards of each other.

Tree age. Apple trees must first mature beforethey will produce fruit. The number of yearsbefore trees begin producing fruit depends onthe rootstock: trees on dwarfing rootstocks bearfruit 3–4 years after planting, while those onseedling rootstocks take 5–7 years.

Heavy pruning. Too much pruning, particu-larly heading cuts into one-year-old wood, willcause trees to produce strong vegetative growth.Trees that are vegetatively invigorated producefew flower buds. Heavy pruning can also removeflower buds once they have formed. Prune treesonly as needed to train the tree to the desiredshape and to allow light into the canopy. Don’tprune trees with hedge shears or similar tools.

Poor training. Trees that have strongly verticallimbs will produce few, if any, fruit. Branchesshould grow at an angle of 60° from vertical.Training branches to grow out rather than upwill increase their fruitfulness. See “Training andPruning” for advice on correcting this problem.

Too much fertilizer. Trees that receive toomuch nitrogen fertilizer produce excessive vege-tative growth. This growth comes at the expenseof fruit production.

Poor fruit qualityIn some instances apple trees produce fruit butthe apples are small and of poor quality. A vari-ety of factors can lead to poor fruit quality.

Fruit from rootstock. Most apple trees are“two-piece trees” composed of a rootstock and ascion. If the scion (which produces fruit of a spe-cific type) is killed but the rootstock continues togrow, the rootstock can produce fruit. This fruitis typically inferior in size, taste, and quality.Occasionally nurseries miss removing a treewhen the scion budding or grafting was unsuc-cessful. If an apple tree is girdled or is killed backto the ground, it is better to replace the tree thanto risk having the rootstock produce fruit.

Neglected plantings. Fruit quality sufferswhen trees are not properly trained, pruned, andfertilized, and when diseases and insect pests arenot kept in check.

Poor growing conditions. Trees planted inpoor sites will likely produce small, poor qualityfruit. Strong shade prevents trees from manufac-turing sufficient carbohydrates to produce qual-ity fruit. Carefully consider site selection beforeplanting.

Inferior cultivars. Inferior cultivars will pro-duce inferior fruit. Also, chance seedlings willlikely produce poor quality fruit. For the bestchance of success, choose cultivars recommendedin Extension publications Apple Cultivars forWisconsin (A2105), Home Fruit Cultivars forNorthern Wisconsin (A2488), and Home FruitCultivars for Southern Wisconsin (A2582).

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Apples

Why plantings failPlant death is usually caused by a number ofinteracting factors rather than by a single identifi-able cause. One injury may provide sufficientstress to allow other problems to eventually killthe tree. Several common reasons for tree deathare described below.

Winter injury. Although apples are generallycold hardy in Wisconsin, extremely cold weatherwill damage the scion or the rootstock or both.Winter-injured trees generally leaf out normallyin the spring and may even flower. The leavesare typically small and narrow and if the damageis severe the tree may die within 4–6 weeks. Thelayer beneath the bark (cambium) is normallycream colored but turns reddish brown whendamaged. Even modest winter injury mayweaken trees making them more susceptible toinsect and disease damage. To minimize winterinjury, select only cultivars that are hardy in yourarea, plant trees in appropriate sites, controlinsect and disease pests, and allow trees to“harden off” by not fertilizing after August 1 andnot pruning after August 15.

Too much water. Apple trees will not tolerate“wet feet.” Poor soil drainage is common in soilswith a high clay content or in low areas. Standingwater lasting more than 1–2 days during the grow-ing season will likely damage the roots. Waterfills the pores in the soil, depriving the roots ofoxygen. Prolonged periods of standing water cre-ate ideal conditions for crown and root rot, a dis-ease that can kill the tree. Avoid these problemsby choosing sites with good soil drainage.

Too little water. Young apple trees are espe-cially susceptible to drought. When water is inshort supply, roots cannot supply enough waterto replace that lost by the leaves through transpi-ration. Sandy soils hold little water and are partic-ularly drought-prone. Prevent drought stress bywatering regularly. Young trees should receive 3–5 gallons of water per week. Irrigation also bene-fits older, bearing trees. Grass growing within 18inches of the trunk of the tree will take up mostof the available water. Remove grass and placemulch around the trunk to conserve water.

Physical damage. Damage to the bark can becaused by small animals feeding in the winterand by lawnmowers and string trimmers. If alarge portion of the bark has been removed, thetree will be weakened but may survive. If a com-plete ring of bark is removed so that the tree isgirdled, the tree will die shortly after growthbegins in the spring. To prevent physical dam-age, keep the area around the tree trunk free ofgrass and weeds. Don’t pile mulch up against thetrunk. This will prevent rodents and rabbits fromnesting and make the trees less attractive as afood source. Keep vegetation around the plantingmowed short, particularly in the fall. Tree trunkscan also be wrapped with wire trunk guardsmade from an 18-inch square of 1⁄4- or 1⁄2-inchmesh hardware cloth. For more informationabout rodent control, see Extension publicationMeadow Mouse Control (A2148).

Deer will also feed on apple trees. Deer tend toeat the tips of the shoots in late winter or earlyspring. When deer browse trees heavily it is moredifficult to train and prune trees correctly. Deermay also rub against young trees, scraping offthe bark and killing the tree. If deer pressure isheavy, only fencing will keep deer away fromtrees. However, if deer pressure is low, repellentscan reduce or eliminate injury. Inexpensive repel-lents include hanging human hair or slaughter-house tankage in fabric net bags in each tree.Small hotel-size bars of soap can also be effectiverepellents. Leave the wrapper on the bar andpoke a hole through the soap and hang it on thetree with a short piece of wire. All repellents lastonly a few weeks to a few months and need to bereplenished often. For more information, seeExtension publication Controlling Deer Damage inWisconsin (G3083).

Insect and disease pests. Severe insectinfestations and disease problems can weakentrees, making them prone to winter injury. Whilethese problems seldom kill trees outright, theyare often contributors. Manage insect pests anddiseases using the practices described earlier inthis publication.

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RELATED PUBLICATIONSFor more information on many of the subjectsdiscussed in this publication, see the resourceslisted below. These publications are availablefrom your county Extension office or fromCooperative Extension Publishing, 877-947-7827or learningstore.uwex.edu.

Cultural informationApple Cultivars for Wisconsin (A2105)

Fruit Crop Pollination (A3742)

Home Fruit Cultivars for Northern Wisconsin(A2488)

Home Fruit Cultivars for Southern Wisconsin(A2582)

Rootstocks for Fruit Trees in Wisconsin (A3561)

Sampling Lawn and Garden Soils for Soil Testing(A2166)

Training and Pruning Apple Trees (A1959)

When are Apples Ripe? (A3743)

Pest managementApple Pest Management for Home Gardeners(A2179)

Cedar-Rust Complex (A2598)

Commercial Tree Fruit Spray Guide (A3314)

Common Tree Fruit Pests (NCR063)

Controlling Deer Damage in Wisconsin (G3083)

Diseases of Tree Fruits in the East (NCR045)

Eastern Tent Caterpillar (A2933)

Fire Blight (A1616)

Meadow Mouse Control (A2148)

Sooty Blotch and Flyspeck (A3173)

Tree Fruits: Insect and Disease Management forBackyard Growers in the Midwest (AIDEA3)

Watercore of Apple (A3280)

I N W I S C O N S I N

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Apples

Copyright © 2006 by the Board of Regents of the University of Wisconsin System doing business as the division ofCooperative Extension of the University of Wisconsin-Extension. Send inquiries about copyright permission to:Manager, Cooperative Extension Publishing, 432 N. Lake St., Rm. 103, Madison, WI 53706.

Authors: Teryl Roper is professor of horticulture, Dan Mahr is professor of entomology, and Patty McManus is professorof plant pathology, College of Agricultural and Life Sciences, University of Wisconsin-Madison and University ofWisconsin-Extension, Cooperative Extension.

Credits: Produced by Cooperative Extension Publishing, University of Wisconsin-Extension. Pruning illustrations andgraphic design by Jody Myer. Cover art by Catherine Baer (© 2000). Fruit fly wing banding patterns drawings come fromTree Fruit Insects (NCR063), courtesy Michigan State University Extension. Japanese beetle illustration by David Shetlar.

University of Wisconsin-Extension, Cooperative Extension, in cooperation with the U.S. Department ofAgriculture and Wisconsin counties, publishes this information to further the purpose of the May 8 and June 30, 1914Acts of Congress; and provides equal opportunities and affirmative action in employment and programming. If youneed this material in an alternative format, contact the Office of Equal Opportunity and Diversity Programs or callCooperative Extension Publishing at 608-262-2655.

This publication is available from your Wisconsin county Extension office or from Cooperative ExtensionPublishing. To order, call toll-free 877-WIS-PUBS (947-7827) or visit online at learningstore.uwex.edu.

A3565 GROWING APPLES IN WISCONSIN SR-12-2006-(R7/00)-2M