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.
PRINCIPLES OF DISEASE MANAGEMENT
Dreistadt et al.. 2004 - p. 21-48, 212-222; 349-472
Agrios Chapter 9
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
Inoculum reduction – removal of stumps and roots for root diseases, raking and removal of infected leaves
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
Best way to prevent powdery mildew and other diseases w/o using chemicals!
Fumigants – methyl bromide, chloropicrin
(still looking for alternative to MB)
Control of insect vectors – e.g., Dutch elm disease
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.
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.
How to treat?
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
Success story for mycorrhizas?
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.
Sudden oak death
Controlled largely by quarantine and plant destruction
The current host list includes:
California black oak, coast live oak, Shreve oak,
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
For each host
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.
Captan 80 WDG ar1.9 to 2.5 lbs/acre
Fixed copper for blossom blight only