Downy mildew—Plasmopara (=Peronospora) spp.
Downy mildew causes problems on various plants including
alyssum, carnation, pansy, poppy, snapdragon, sunflower,
and sweet pea. Downy mildew causes soft and fluffy gray,
purplish, or light brown sporulation on the underside of
leaves and sometimes on stems or buds. Pale
yellow areas or irregular purplish red to dark brown necrotic
lesions are sometimes visible on the upper surface of infected
leaves.
Solutions
Provide good air circulation and maintain
low humidity. Avoid wetting foliage; use drip instead
of overhead irrigation where feasible. Dig out infected
plants as soon as possible to reduce the spread of disease. Several
fungicides can prevent infection of healthy tissue, and fungicide
use may be necessary to prevent damage to susceptible plants
if conditions are good for disease development.
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Yellow blotches on upper surface of leaf
Grayish patches of powdery growth on the underside of a leaf
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