Post on 20-Dec-2015
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