Reading:Dreistadt et al.. 2004 - p. 21-48, 212-222; 349-472Agrios Chapter 9PNW Plant Disease Management Handbook

Lecture 19PRINCIPLES OF DISEASE MANAGEMENT

Disease management (control)From PNW Plant Disease Management Handbook

Exclusion – quarantines, inspections, certificationAvoidance – not planting in poorly drained soils (Phytophthora), avoiding woundingEradication – crop rotation, sanitation, eliminating alternate hosts, fumigationProtection – treating healthy plants before infection - fungicidesResistance – genetic resistance – tolerance, immunity

PRINCIPLES OF DISEASE MANAGEMENT

1. CULTURAL

2. CHEMICAL

3. GENETIC - BREEDING FOR RESISTANCE/ BIOTECHNOLOGY

4. BIOLOGICAL CONTROL

5. QUARANTINE

6. DOING NOTHING

              1. CULTURALPractices for producing healthy plants

Improved growing conditions – fertilization, soil organic matter, good drainage, avoid compactionHost removalInoculum reduction – removal of stumps and roots for root

diseases, raking and removal of infected leavesPruning, thinningCrop rotationSanitation – debarking for Dutch elm disease, leaf rakingUse of alternative species – red cedar for laminated root rotMulches - polyethylene tarps, bark, wood chipsSuppressive soils/antagonism of other microbesAntagonistic plants - mustardPhysical methods – heat (black or clear plastic, steam), light, refrigeration

Verticillium wilt – Japanese maple

Rose Powdery Mildew and Common Cultural Methods for

Control

Powdery Mildew

(Sphaerotheca pannosa)

• Overwinters in infected buds, canes and fallen leaves and attacks young spring growth.

• Thrives in areas with high relative humidity at night when temperatures are around 60 degrees F.

• Also thrives at around 80 degrees F with 40%-70% RH.

Best way to prevent powdery mildew and other diseases w/o using chemicals!

• Clean up fallen leaves, deadheads and other debris. DO NOT COMPOST!

• Allow adequate space for plants when planting to ensure good air circulation.

• Avoid overwatering, overhead watering, and applying too much fertilizer.

• Plant “resistant” varieties

2. CHEMICAL METHODS

Fungicides

Fumigants – methyl bromide, chloropicrin (still looking for alternative to MB)

Control of insect vectors – e.g., Dutch elm disease

Fungicide application to control ergot on rye

Ethanedinitrile – MB alternative

Agriculture fumigation

Forest nursery fumigation

Fumigant application methods

FUNGICIDES Classified by chemical class or mode of action orby properties once in the plant. a. Chemical class – organic or inorganic - best to mix or rotate materials found in

different fungicide families.

b. Mode of action and properties in the plant (terms)

Antibiotics - Streptomycin against fire blightBiofungicides – Trichoderma harzianum, Pseudomonas syringae, Bacillus subtilis, Verticillium dahliaeBroad spectrum - captan, sulfurNarrow spectrum - metalaxyl against PhytophthoraBroad to narrow spectrum

Bactericidal Curative - generally act within the plant and are effective shortly after penetrationDemethylation-inhibiting - funginexEradicant (contact killing, prevent sporulation)Fungicidal - kills fungi - CaptanFungistatic - inhibit fungi (metalaxyl)Fumigant - vapor action (methyl bromide)NematicideProtectants - prevent spores from germinating - BravoSystemic - usually absorbed by roots and translocated through plant (metalaxyl) some move downward (Aliette - stimulates host defense mechanisms)Locally systemic - don't move far in the plant – Thiophanate methylVapor action - fumigants

c. Common fungicides in the home landscape (multiple modes of action)

Captan - broad spectrum - leaf spots, blights (not good against powedery mildews and rust)

Chlorothaninol (Daconil 2878, Fung-onil, Bravo) - broad spectrum. Foliar treatment

Copper based compounds (Bordeaux mix , copper sulfate) downy mildew on grapes, many fungal and bacterial leaf diseases and cankers

Horticultural and botanical oils (Neem oil, pesticidal oil) – good eradicants – powdery mildew

Lime sulfur or calcium polysulfide (Lime sulfur) - eradicant and dormant spray - powdery mildew, scab, brown rot, leaf curls, rusts and mites - can burn

Mancozeb (Greenlight broad spectrum) – fungal diseases - lawns, fruits, vegetables, ornamentals

Mycobutanil (Immunox, Spectricide) – powdery mildews,rusts, leaf spots

PCNB (pentachloronitrobenzene) - soil fungicide – lawn snow mould

Soaps (Safer’s Insecticidal Soap) – powdery mildews

Sodium or Potassium bicarbonates – not very effective

Streptomycin (Fire Blight Spray)

Sulfur (Safer’s Garden Fungicide) - elemental sulphur - powdery mildew and leaf blights - can burn

Thiophanate methyl (Green Light Systemic Fungicide)- ornamentals, lawns, some fruit trees

Triforine (Funginex) - locally systemic - powdery mildews, leaf spots, blights  

Compost tea – foliage diseases. Does it work?

Fungicides may also need spray adjuvant to work - stickers, etc.

Rhododendron - Phytophthora root diseaseHow to treat?

3. BREEDING FOR RESISTANCE/ BIOTECHNOLOGY

Resistant species and varieties, molecular techniques - gene transfer

Resistant cherry in Arboretum?

4. BIOLOGICAL CONTROL

With antagonistic fungi and bacteria, mycorrhizae, antibiotics

Fungi Trichoderma harzianum, Verticillium dahliae

Bacteria Pseudomonas syringae, Bacillus subtilis

BIOLOGICAL CONTROL

MYCORRHIZAEMycorrhizae (fine root/fungal muutalistic symbiotic association)- Fungus protects plants against pathogens

Mix of ectomycorrhizae and arbuscular mycorrhizae

Phytophthora lateralis in the ArboretumSuccess story for mycorrhizas?

Biological control of Dutch elm disease Dutch Trig

A suspension of live spores of the fungus Verticilliumdahliae injected into the tree by gouge pistol. Protects by inducing resistance in the tree

Pros

Small injection holes, rapid, less costly than fungicide

Cons

Must be applied every yearV. dahliae is a plant pathogenOnly an option before infection

5. QUARANTINE

Excluding diseased plants, seeds, bulbsor contaminated soil, machinery, etc.

Introduced pathogensSudden oak death

The current host list includes: California black oak, coast live oak, Shreve oak,tanoak, rhododendron,California bay laurel, big leaf maple, madrone, manzanita, huckleberry, California honeysuckle, toyon,California buckeye, California coffeeberry,Douglas-fir and coast redwoodand Arrow wood (in Germany, the United Kingdom, and the Netherlands).

SUDDEN OAK DEATH Controlled largely by quarantine and plant destruction

6. DOING NOTHING

How much disease are youprepared to handle?

Decay in trees could providewildlife habitat, but couldallow development of hazardtrees

PNW Plant Disease Management Handbook

For each host

• Cause

• Symptoms

• Cultural control

• Chemical control

• References

Cherry brown rot in Arboretum

Brown rot mummies

Cherry brown rot

• Cause – two fungal species (Monilinia fructicola and M. laxa)

incites blossom blight, twig and branch dieback, fruit rot of ornamental and fruit trees – cherries, peaches, nectarines, prunes, plums, almonds and apricots. More of a problem west of Cascade crest. Wind and rain blow ascospores and conidia to healthy blossoms in spring from mummies.

Cherry brown rot continued.

Symptoms

• Infected flower parts turn light brown or gray; water soaked flowers; branch girdling; profuse gumming; fruit symptoms dark spots with buff-colored spores

Brown rot continued

Cultural control• Remove and control infected twigs and branches a• Remove and destroy mummified fruit• Use moderate amounts of N fertilizer

Brown rot continued

Chemical control• Apply fungicides during the bloom period

at early popcorn, full bloom, and/or petal fall with alternate fungicides

• 26 different fungicides are available Captan 80 WDG ar1.9 to 2.5 lbs/acre Fixed copper for blossom blight only Wettable sulfur