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How to Manage Pests

UC Pest Management Guidelines


Flowers of China aster, Callistephus chinensis.

Floriculture and Ornamental Nurseries

Aster, China (Callistephus chinensis)

Disease Control Outlines

(Reviewed 3/09, updated 3/09)

In this Guideline:


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 *

[Precautions]

PUBLICATION

[UC Peer Reviewed]

UC IPM Pest Management Guidelines: Floriculture and Ornamental Nurseries
UC ANR Publication 3392
Diseases
S. T. Koike, UC Cooperative Extension Monterey County
C. A. Wilen, UC IPM Program, UC Cooperative Extension San Diego County
Acknowledgment for contributions to Diseases:
R. D. Raabe, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
A. H. McCain, (emeritus) Environmental Science, Policy, and Management (ESPM), UC Berkeley
M. E. Grebus, Plant Pathology, UC Riverside

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