| Disease (causal agent) |
Symptoms |
Survival of pathogen and effect of environment |
Comments on control |
Fusarium wilt
(Fusarium oxysporum f. sp. callistephi) |
Plants yellow and wilt, often on one side.
Brown discoloration of vascular system develops. Disease also causes damping‑off of young seedlings at soil temperatures of 75° to 80°F. |
Commonly seedborne. In soil for many years. Disease is most severe when soil and/or air temperatures are high. |
Use disease‑free seed. Fumigate the
seedbed with chloropicrin-methyl bromide combination or solarize soil. Grow
on clean land, or only once every 5 years on infested land. Treat seed with a
fungicide. more info * |
Gray mold
(Botrytis cinerea) |
Brown, water‑soaked decay of flowers.
Woolly gray fungus spores form on rotted tissues. Fungus also attacks base of plant. |
In plant debris. Favored by cool, wet conditions. |
Avoid overhead irrigation. Mist blooms with
iprodione or fenhexamid. more
info * |
Leaf spots
(Stemphylium callistephi) |
Circular, irregular, brown spots appear on lower leaves. Leaves may die. |
In plant debris. Airborne spores require long (48 hrs), damp periods for infection. |
Avoid low‑lying areas where air
movement is poor. Do not use overhead irrigation. Protect foliage with a fungicide such as mancozeb. |
Root rot
(Pythium and
Phytophthora spp.) |
Plants wilt or suddenly collapse. Roots
decay. Blackish discoloration of leaves, stems, and roots occurs. Also causes damping‑off of seedlings. |
In soil. Favored by heavy, waterlogged soils. |
Avoid planting in poorly drained fields. Plant on raised
beds. Do not overirrigate and keep hose ends off the ground. Drench seedlings
with mefenoxam. more info: Pythium Root Rot, Phytophthora Root and
Crown Rots* |
Rust
(Coleosporium asterum) |
Orange pustules of powdery spores form on
undersides of leaves. On living plants and possibly from spores from alternate host (three‑needle pines). |
Favored by free moisture from rain, dew, or fog. Very common in cut-flower-growing areas around San Jose. |
Avoid overhead irrigation. Treat at the
first signs of rust and continue until conditions are no longer favorable for
the disease. Grow seedlings away from main crop. more info * |
Sclerotinia rot or Cottony rot
(Sclerotinia sclerotiorum) |
Infection girdles stems. Cottony, white
fungal growth and large, black sclerotia develop on and inside stems. Stems take on a bleached‑white color. |
Airborne spores produced by sclerotia in
soil, but infection more common from growth of hyphae from sclerotia. Favored by wet weather. |
Avoid overhead irrigation. Treat planting
area with PCNB. Spray plants with iprodione or thiophanate-methyl before
rainy periods and at 2- to 4-week intervals during wet weather. Remove plant
debris from field. more info: Cottony Rot, Southern
Blight * |
Stem rot
(Rhizoctonia solani, Botrytis cinerea) |
A brown decay develops at the soil line and affects the basal leaves and stem. |
Soilborne and in plant debris. Gray mold (B.
cinerea) favored
by cold, damp conditions. Disease development can be rapid under high temperature conditions. |
Before planting or transplanting, mix PCNB
or Trichoderma spp. into top inch of soil. Spray bases of seedlings with
thiophanate-methyl, iprodione, or Trichoderma spp. |
Verticillium wilt
(Verticillium dahliae) |
Symptoms are almost identical to Fusarium wilt. Not a common disease of asters in California. |
In soil for many years. Symptoms most severe during warm weather that follows a cool period. |
Avoid planting in fields where fungus has
occurred or fumigate soil as described for Fusarium wilt. more info * |
| |
| Virus or viruslike diseases |
Symptoms |
Host range and natural spread |
Comments on control |
Aster yellows
(Aster yellows phytoplasma) |
Infected plants produce an upright basal
rosette of yellow shoots. Sometimes one-sided. Flowers are deformed and remain green. Sporadic disease of asters in California. |
Aster yellows phytoplasma has a wide host
range. Vectored by leafhoppers. |
Locate seedbed away from weedy areas. Control weeds and
leafhoppers in noncropped areas. more info * |
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