| Disease (causal agent) | Symptoms | Survival of pathogen and effect of environment | Comments on control |
|---|---|---|---|
| Downy mildew * (Plasmopara halstedii and Bremia lactucae) |
Two distinct downy mildews infect strawflower, though symptoms are similar for both diseases: yellow foliage with downy white sporulation on the undersurface. Leaves roll downward. Tissues sometimes are killed | Disease is favored by cool (59°F), wet weather. Spores (sporangia) are airborne. Chilean tarweed (Madia sativa) and other members of the family Compositae are hosts of P. halstedii. | Control tarweed for some distance away if possible. Protective fungicides should be effective but few if any are labeled for strawflower. |
| Verticillium wilt * (Verticillium dahliae) |
Wilting and yellowing of lower leaves on one side of plant. Vascular discoloration. | Favored by cool spring. Symptoms develop rapidly in hot weather at flowering. Fungus survives in soil for long periods as microsclerotia. Many plants are infected including weeds, crop plants, and ornamentals. | Avoid fields that are known to be infested. Soil fumigation with chloropicrin or a chloropicrin combination is effective. |
| Virus or viruslike disease | Symptoms | Host range and natural spread | Comments on control |
| Aster yellows * (Aster yellows phytoplasma) |
Plants stunted and yellow. Frequently one-sided. Flowers may be green. | Aster yellows phytoplasma is spread by leafhoppers. A wide variety of plants including weeds are susceptible. | Control weeds in and around planting. Leafhopper control may help. |
| * For additional information, see section on Key Diseases. |