Reading

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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
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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

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• PRINCIPLES OF DISEASE MANAGEMENT
• CULTURAL
• CHEMICAL
• GENETIC - BREEDING FOR RESISTANCE/ BIOTECHNOLOGY
• BIOLOGICAL CONTROL
• QUARANTINE
• DOING NOTHING

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1. CULTURAL 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
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Verticillium wilt Japanese maple
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Rose Powdery Mildew and Common Cultural Methods
for Control

• 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

• 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.

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2. CHEMICAL METHODS Fungicides Fumiga
nts methyl bromide, chloropicrin (still
looking for alternative to MB) Control of insect
vectors e.g., Dutch elm disease
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Fungicide application to control ergot on rye
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Agriculture fumigation
Ethanedinitrile MB alternative
Forest nursery fumigation
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Fumigant application methods
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FUNGICIDES   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.
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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

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Bactericidal 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)
Nematicide 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
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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
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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 (Safers Insecticidal Soap)
powdery mildews Sodium or Potassium bicarbonates
not very effective
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Streptomycin (Fire Blight Spray) Sulfur (Safers
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.
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Rhododendron - Phytophthora root disease How to
treat?
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3. BREEDING FOR RESISTANCE/
BIOTECHNOLOGY Resistant species and varieties,
molecular techniques - gene transfer
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Resistant cherry in Arboretum?
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4. BIOLOGICAL CONTROL With
antagonistic fungi and bacteria,
mycorrhizae, antibiotics Fungi
Trichoderma harzianum, Verticillium dahliae
Bacteria Pseudomonas syringae, Bacillus
subtilis
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BIOLOGICAL CONTROL MYCORRHIZAE Mycorrhizae
(fine root/fungal muutalistic symbiotic
association) - Fungus protects plants against
pathogens Mix of ectomycorrhizae and
arbuscular mycorrhizae
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Phytophthora lateralis in the Arboretum Success
story for mycorrhizas?
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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 Pros Small injection holes, rapid,
less costly than fungicide Cons Must be applied
every year V. dahliae is a plant pathogen Only an
option before infection
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5. QUARANTINE Excluding
diseased plants, seeds, bulbs or contaminated
soil, machinery, etc. Introduced
pathogens Sudden oak death
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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).
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6. DOING NOTHING How much disease are
you prepared to handle? Decay in trees could
provide wildlife habitat, but could allow
development of hazard trees
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PNW Plant Disease Management Handbook

• For each host
• Cause
• Symptoms
• Cultural control
• Chemical control
• References

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Cherry brown rot in Arboretum
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Brown rot mummies
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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.

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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

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Brown rot continued

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

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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