4. PRINCIPLES OF DISEASE MANAGEMENT
1. CULTURAL
2. CHEMICAL
3. GENETIC - BREEDING FOR RESISTANCE/
BIOTECHNOLOGY
4. BIOLOGICAL CONTROL
5. QUARANTINE
6. DOING NOTHING
5. 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
7. 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
8.
9. 2. CHEMICAL METHODS
Fungicides
Fumigants – methyl bromide, chloropicrin
(still looking for alternative to MB)
Control of insect vectors – e.g., Dutch elm
disease
14. 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.
15. 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
16. 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
17. 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
18. 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
19. 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.
26. 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
27. 5. QUARANTINE
Excluding diseased plants, seeds, bulbs
or contaminated soil, machinery, etc.
Introduced pathogens
Sudden oak death
28. 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).
SUDDEN OAK DEATH
Controlled largely by
quarantine and plant destruction
29. 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
30. PNW Plant Disease Management Handbook
For each host
• Cause
• Symptoms
• Cultural control
• Chemical control
• References
33. 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.
34. 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
35. Brown rot continued
Cultural control
• Remove and control infected twigs and branches a
• Remove and destroy mummified fruit
• Use moderate amounts of N fertilizer
36. 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
