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Reading: Dreistadt et al.. 2004 - p. 21-48, 212-222; 349-472 Agrios Chapter 9 - PowerPoint PPT Presentation

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Lecture 19 PRINCIPLES OF DISEASE MANAGEMENT. Reading: Dreistadt et al.. 2004 - p. 21-48, 212-222; 349-472 Agrios Chapter 9 PNW Plant Disease Management Handbook. Disease management (control) From PNW Plant Disease Management Handbook.

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Lecture 19



Dreistadt et al.. 2004 - p. 21-48, 212-222; 349-472

Agrios Chapter 9

PNW Plant Disease Management Handbook

Disease management control from pnw plant disease management handbook

Disease management (control)From PNW Plant Disease Management Handbook

Exclusion – quarantines, inspections, certification

Avoidance – not planting in poorly drained soils (Phytophthora), avoiding wounding

Eradication – crop rotation, sanitation, eliminating alternate hosts, fumigation

Protection – treating healthy plants before infection - fungicides

Resistance – genetic resistance – tolerance, immunity


Practices for producing healthy plants

Improved growing conditions – fertilization, soil organic matter, good drainage, avoid compaction

Host removal

Inoculum reduction – removal of stumps and roots for root diseases, raking and removal of infected leaves

Pruning, thinning

Crop rotation

Sanitation – debarking for Dutch elm disease, leaf raking

Use of alternative species – red cedar for laminated root rot

Mulches - polyethylene tarps, bark, wood chips

Suppressive soils/antagonism of other microbes

Antagonistic plants - mustard

Physical methods – heat (black or clear plastic, steam), light, refrigeration

Rose powdery mildew and common cultural methods for control
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



Fumigants – methyl bromide, chloropicrin

(still looking for alternative to MB)

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

Agriculture fumigation

Forest nursery fumigation

Ethanedinitrile – MB alternative


Classified by chemical class or mode of action or

by 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 blight

Biofungicides – Trichoderma harzianum, Pseudomonas syringae, Bacillus subtilis, Verticillium dahliae

Broad spectrum - captan, sulfur

Narrow spectrum - metalaxyl against Phytophthora

Broad to narrow spectrum


Curative - generally act within the plant and are effective shortly after penetration

Demethylation-inhibiting - funginex

Eradicant (contact killing, prevent sporulation)

Fungicidal - kills fungi - Captan

Fungistatic - inhibit fungi (metalaxyl)

Fumigant - vapor action (methyl bromide)


Protectants - prevent spores from germinating - Bravo

Systemic - 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 methyl

Vapor 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.


Resistant species and varieties, molecular techniques - gene transfer


With antagonistic fungi and bacteria, mycorrhizae, antibiotics


Trichoderma harzianum, Verticillium dahliae


Pseudomonas syringae, Bacillus subtilis



Mycorrhizae (fine root/fungal muutalistic symbiotic


- Fungus protects plants against pathogens

Mix of ectomycorrhizae and arbuscular mycorrhizae

Phytophthora lateralis in the Arboretum

Success story for mycorrhizas?

Biological control of Dutch elm disease

Dutch Trig

A suspension of live spores of the fungus Verticillium

dahliae injected into the tree by gouge pistol. Protects by inducing resistance in the tree


Small injection holes, rapid, less costly than fungicide


Must be applied every year

V. dahliae is a plant pathogen

Only an option before infection


Excluding diseased plants, seeds, bulbs

or contaminated soil, machinery, etc.

Introduced pathogens

Sudden oak death


Controlled largely by quarantine and plant destruction

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 redwood

and Arrow wood (in Germany,

the United Kingdom, and the Netherlands).


How much disease are you

prepared to handle?

Decay in trees could provide

wildlife habitat, but could

allow development of hazard


Pnw plant disease management handbook
PNW Plant Disease Management Handbook

For each host

  • Cause

  • Symptoms

  • Cultural control

  • Chemical control

  • References

Cherry brown rot
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
Cherry brown rot continued.


  • 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
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 continued1
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