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Competency Area 3: Management of Infectious Plant Diseases

PO 22. For each of the following field crop diseases:

  1. Classify by type of pathogen
  2. Know the type of symptoms produced and plant parts affected
  3. Know what conditions favor disease development
  4. Know how the pathogen survives between crop seasons
  5. Know other crop species attacked by the pathogen
  6. Know how the pathogen is spread

and

PO 23. For the field crop diseases listed under (22) above, know the availability and relative usefulness in disease management under Northeast conditions of:

  1. Seed-, foliar-, and soil-applied fungicides
  2. Resistant or tolerant crop varieties
  3. Use of certified seed
  4. Other cultural practices such as rotation, tillage, site selection, soil drainage, planting time, harvest time, fertility, weed and insect control

Causal agents of Infectious plant diseases:

Fungus: (fungi- plural) is a non-photosynthesizing eukaryote that produces enzymes to break down matter and absorb its food.  A fungus usually produces and lives inside a network of apically extending, branching tubes called hyphae.  It produces reproductive structures called spores. Fungi have chitin in their cell walls, hyphae are septate and they are non-motile.

Oomycete: (oomycetes-plural) or water mold(s) is a non-photosynthesizing eukaryote in the Kingdom Protista that produces enzymes to break down matter and absorb its food. Water molds occupy similar ecological niches to fungi but are most closely related to slime molds, protozoans, and algae.  It produces structures called spores and these spores are motile (they swim by means of flagella). Oomycetes have cellulose in their cell walls, hyphae are nonseptate and spores are motile.
Bacteria: (bacterium-singular) are single-celled microscopic organs which multiply by division.
Viruses: (virus-singular) are very small particles that consist of genetic material encased in a protein capsule; they can only reproduce within a living organism. Viruses are spread by insects such as aphids and leafhoppers; in planting material such as vegetative propagules and seeds; and mechanically when contaminated implements come in contact with plants.
Nematode: (nematodes-plural) is a worm-like animal. All plant parasitic nematodes are microscopic in size.

DISEASES OF ALFALFA

Anthracnose - F
Disease Type Fungus
Symptoms Stem lesions, wilt
Host Plants Alfalfa, Clover
Survival and Spread Rain-splashed spores (from debris/plants)
Favored by Warm moist weather
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (1), Remove debris from equipment (2)

Brown root rot - F
Disease Type Fungus
Symptoms Root/crown rot
Host Plants Legumes, grasses
Survival and Spread In soil
Favored by Stresses that weaken plants
Control measures and effectiveness (1=high to 3= slight) Reduce plant injury/stress (3)

Leaf and stem blight complex including spring black stem and leaf spot, lepto leaf spot, andcommon leaf spot – F
Disease Type Fungus
Symptoms Leaf, stem lesions
Host Plants Small-seeded legumes
Survival and Spread Rain-splashed or airborne spores from infected debris or plants
Favored by Moist conditions
Control measures and effectiveness (1=high to 3= slight) Harvest early to reduce leaf loss (3)

Fusarium crown and root rot - F
Disease Type Fungus
Symptoms Root/ crown rot
Host Plants Many hosts
Survival and Spread In soil
Favored by Stressed plants; clover root curculio; injured crowns
Control measures and effectiveness (1=high to 3= slight) Reduce plant injury/stress (3)

Phytophthora root rot - O
Disease Type Oomycete
Symptoms Root rot
Host Plants Alfalfa
Survival and Spread In soil
Favored by Wet soils
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (1), Anti-oomycete seed fungicides (2), Soil drainage (2)

Pythium damping-off - O
Disease Type Oomycete
Symptoms Root/shoot rot
Host Plants many hosts
Survival and Spread In soil
Favored by Cool, moist soil
Control measures and effectiveness (1=high to 3= slight) Anti-oomycete seed treatments (1) Good seedbed preparation (2) Soil drainage (2)

Verticillium wilt - F
Disease Type Fungus
Symptoms Stem lesions, wilt
Host Plants many dicot plants
Survival and Spread Soilborne, contaminated harvest equipment
Favored by Cool, wet weather
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (1) Rotation with cereals/grasses (3)

DISEASES OF CORN

Anthracnose leaf blight and stalk rot - F
Disease Type Fungus
Symptoms Leaf blight, stalk rot
Host Plants Corn
Survival and Spread Rain-splashed spores (local) from corn debris
Favored by Mild, wet; reduced-till, continuous corn; European corn borer injury to stems
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1-2) Crop rotation (2) Clean plowing (2) Corn borer-resistant (Bt) hybrids (1-2)

Common rust - F
Disease Type Fungus
Symptoms Leaf rust
Host Plants Corn
Survival and Spread Airborne spores (long distance)
Favored by Humid; thunderstorms
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1) Timely planting (2)

Common smut - F
Disease Type Fungus
Symptoms Galls on ears, tassel, and leaves
Host Plants Corn
Survival and Spread Airborne and rain-splashed spores (in soil)
Favored by Injuries; dry conditions
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1) Fertilize based on soil tests (2)

Eyespot - F
Disease Type Fungus
Symptoms Leaf lesions
Host Plants Corn
Survival and Spread Rain-splashed spores (local) from corn debris
Favored by Cool, wet; reduced-till; continuous corn
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1) Crop roatation (2) Clean plowing (2)

Gibberella (red) ear rot - F
Disease Type Fungus
Symptoms Ear rot, mycotoxins
Host Plants Cereals, grasses
Survival and Spread Airborne spores (regional) from corn debris
Favored by Moisture at silk emergence
Control measures and effectiveness (1=high to 3= slight) Adapted, less susceptible hybrids (2) Timely planting & harvest (3) Fertilize based on soil test (3) Reduce stress (3)

Gibberella stalk rot - F
Disease Type Fungus
Symptoms Stalk rot
Host Plants Cereals, grasses
Survival and Spread Invasion through roots (soil) or wounds
Favored by Stressed plants
Control measures and effectiveness (1=high to 3= slight) Adapted, tolerant hybrids (2) Timely planting & harvest (3) Fertilize based on soil test (3) Reduce stress (3)

Gray leaf spot - F
Disease Type Fungus
Symptoms Leaf lesions
Host Plants Corn
Survival and Spread Airborne spores (regional) from corn debris
Favored by Persistent dew, fog; reduced-till, continuous corn
Control measures and effectiveness (1=high to 3= slight) partially resistant hybrids (2) Crop rotation (2) Clean plowing (2)

Northern leaf blight - F
Disease Type Fungus
Symptoms Leaf lesions
Host Plants Corn
Survival and Spread Airborne spores (long distance) from corn debris
Favored by Humid, wet
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1-2) Timely planting (2)

Northern (carbonum) leaf spot - F
Disease Type Fungus
Symptoms Leaf lesions
Host Plants Corn
Survival and Spread Airborne spores (long distance)
Favored by Humid, wet
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1) Timely planting (2)

Seed decay/seedling blights – F, O, B
Disease Type Fungus, oomycetes, bacteria
Symptoms Attack seeds and seedlings
Host Plants Many hosts
Survival and Spread In soil; seed
Favored by Cool, moist soil; poor quality seed
Control measures and effectiveness (1=high to 3= slight) Protectant seed fungicides (1) Good seedbed preparation (2) Timely planting (2)

Stewart’s leaf blight - B
Disease Type Bacteria
Symptoms Leaf blight, systemic
Host Plants Corn
Survival and Spread Corn flea beetle
Favored by Mild winter preceding crop season
Control measures and effectiveness (1=high to 3= slight) Resistant hybrids (1)

DISEASES OF OATS

Crown rust – F
Disease Type Fungus
Symptoms Leaf rust
Host Plants Oat, buckthorn
Survival and Spread Airborne spores from infected oat or buckthorn
Favored by Warm, humid; thunderstorms in June/July
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (race-specific)(1-2), Plant early in the spring (2)

Yellow dwarf (red leaf) – V
Disease Type Virus
Symptoms Reddens leaves, stunting
Host Plants Many cereals and grasses
Survival and Spread By aphids (short and long distance)
Favored by late planting of spring oat; large aphid populations
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (virus strain-specific) (1-2), Plant early in the spring (2)

DISEASES OF WHEAT

Fusarium head blight (scab) – F
Disease Type Fungus
Symptoms Head, kernel blight, mycotoxins contamination
Host Plants Cereals and grasses
Survival and Spread Airborne spores (regional) and rain-splashed spores (local) from corn and cereal debris
Favored by Moisture at crop flowering through early grain filling
Control measures and effectiveness (1=high to 3= slight) Follow a non-cereal crop (3) Plant less susceptible varieties (2) Stagger planting dates (3) Systemic foliar fungicides at flowering(2)

Leaf rust – F
Disease Type Fungus
Symptoms Leaf rust
Host Plants Wheat only
Survival and Spread Airborne spores (long distance)
Favored by Warm humid; thunderstorms in June
Control measures and effectiveness (1=high to 3= slight) Timely planting (2) Foliar fungicides (2)

Septoria tritici blotch – F
Disease Type Fungus
Symptoms Leaf blotch
Host Plants Wheat
Survival and Spread Wheat debris; windborne
Favored by Splashing rain; extended leaf wetness
Control measures and effectiveness (1=high to 3= slight) Foliar fungicides (1)

Stagonospora nodorum blotch – F
Disease Type Fungus
Symptoms Leaf glume blotch
Host Plants Wheat
Survival and Spread In seeds; wheat debris; windborne
Favored by Splashing rain; extended leaf wetness
Control measures and effectiveness (1=high to 3= slight) Seed fungicides (3) Foliar fungicides (1)

Loose smut – F
Disease Type Fungus
Symptoms Kernel replacement by spores
Host Plants Wheat only
Survival and Spread In seed (embryo)
Favored by Bin-run seed
Control measures and effectiveness (1=high to 3= slight) Certified seed (1) Systemic seed fungicides (1)

Powdery mildew – F
Disease Type Fungus
Symptoms Mildew on all plant surfaces
Host Plants Wheat only
Survival and Spread Airborne spores (regional)
Favored by Humid; moderate temperatures
Control measures and effectiveness (1=high to 3= slight) Systemic seed fungicides (2) Systemic foliar fungicides (1) resistant varieties (2)

Tan spot – F
Disease Type Fungus
Symptoms Leaf apot
Host Plants Wheat
Survival and Spread Wheat debris; In seed; windborne spores
Favored by Wheat after wheat; humid moderate temperatures; rainfall
Control measures and effectiveness (1=high to 3= slight) Seed fungicides (2) Foliar fungicides (1) Partially resistant varieties (2)

Soilborne wheat mosaic – V
Disease Type Virus
Symptoms Foliar mosaic; stunting
Host Plants Wheat, triticale
Survival and Spread Transmitted by protozoan; persists in soil for many years; limited distribution in the Northeast
Favored by Soil moisture at seedling stages; cool spring temperatures
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (1

Wheat spindle streak mosaic – V
Disease Type Virus
Symptoms Spindle shaped yellow streaks on leaves in spring
Host Plants Wheat
Survival and Spread Transmitted by protozoan; persists in soil for many years; widespread in the Northeast
Favored by Soil moisture at seeding stages; extended cool spring temperatures
Control measures and effectiveness (1=high to 3= slight) Resistant varieties (1)

Yellow dwarf - V
Disease Type Virus
Symptoms Yellowing of leaves, stunting of plants
Host Plants Many cereals and grasses
Survival and Spread Transmitted by aphids (short and long distances)
Favored by Early planting; high aphid populations; nearby infected grasses
Control measures and effectiveness (1=high to 3= slight) Plant after Hessian fly free date (2) Systemic seed insecticides (2)

DISEASES OF SOYBEAN

Asian soybean rust – F
Disease Type Fungus
Symptoms Rust on leaves
Host Plants Soybean, kudzu, perhaps other legumes
Survival and Spread Windborne spores (long distance)
Favored by Early arrival of windborne spores; moderate temperatures; rain
Control measures and effectiveness (1=high to 3= slight) Application of protectant fungicides prior to infection (1-2) Timely application of fungicides with systemic, curative activity (1)

Bacterial blight – B
Disease Type Bacteria
Symptoms Lesions on leaves and pods
Host Plants Soybeans
Survival and Spread Rain-splashed bacteria from soybean debris; cultivation in wet conditions
Favored by Cool wet weather
Control measures and effectiveness (1=high to 3= slight) High quality seeds (2) Crop rotation (2) Avoid highly susceptible varieties (2)

Bacterial pustule – B
Disease Type Bacteria
Symptoms Lesions on leaves and pods
Host Plants Soybeans
Survival and Spread Rain-splashed bacteria debris in soil; cultivation in wet conditions
Favored by Wet conditions
Control measures and effectiveness (1=high to 3= slight) High quality seeds (2) Crop rotation (2) Avoid highly susceptible varieties (2)

Downy mildew – O
Disease Type Oomycete
Symptoms Mildew on leaves, pods, and seeds
Host Plants Soybeans
Survival and Spread Windborne sporangia; systemic infection from infected seeds
Favored by High humidity; moderate temperatures
Control measures and effectiveness (1=high to 3= slight) Crop rotation (2) Anti-oomycete seed treatments (2)

Pod and stem blight – F
Disease Type Fungus
Symptoms Pods and stem lesions
Host Plants Soybean
Survival and Spread Rain-splashed spores from infected soybean debris
Favored by Prolonged moist periods during pod maturation
Control measures and effectiveness (1=high to 3= slight) Crop rotation (2) Adapted varieties (2) Timely harvest (2) late season foliar application if warranted by disease pressure (1)

Sclerotinia stem rot – F
Disease Type Fungus
Symptoms Rot of stems
Host Plants many dicot plants
Survival and Spread Windborne spores from sclerotia on soil surface
Favored by Dense canopy; moisture at flowering; disease in previous crop
Control measures and effectiveness (1=high to 3= slight) Tolerant/resistant varieties (2) Crop rotation (2) Wide row spacing (2)

Septoria brown spot – F
Disease Type Fungus
Symptoms
Host Plants
Survival and Spread Infected soybean debris; seedborne
Favored by Splashing rain; moist conditions; soybean after soybean
Control measures and effectiveness (1=high to 3= slight) Crop rotation (2) Foliar fungicides, if warranted by disease pressure (1)

Soybean cyst nematode – N
Disease Type Nematode
Symptoms Colonizes roots, stunts plants
Host Plants Soybean only
Survival and Spread In soil; movement on equipment, unclean seeds
Favored by Infested local soil from which nematode may be introduced into new fields
Control measures and effectiveness (1=high to 3= slight) Avoid introduction (1) Resistant varieties (1) Crop rotation (2)

Soybean mosaic – V
Disease Type Virus
Symptoms Mosaic on leaves, stunts plants
Host Plants Soybean
Survival and Spread Aphid transmitted (non-persistent) from infected live hosts; seed transmitted
Favored by High aphid populations when plants are young
Control measures and effectiveness (1=high to 3= slight) Plant virus-free seed (1) Timely planting (2) Resistant varieties (strain specific) (2)