What Is It? | Facts for Depth | For the Professional Diagnostician
Brassica Diseases | Downy Mildew
Downy Mildew
Identification
- Cotyledons and primary leaves are invaded first, resulting in fungal growth visible on the underside of the leaf
- Chlorosis develops on the upper side of the leaf
- Premature leaf drop in severely chlorotic leaves
- Lesions on older leaves gradually enlarge, turn bright yellow, and become tan and papery
- In rare cases, the infected leaves may develop hundreds of minute darkened specks.
- Under cool, moist conditions, a white mildew forms on the undersides of leaf lesions
- The disease progresses systemically through the plant
- Dark grey-black, sunken spots develop on cauliflower curds and cabbage heads, often followed by secondary invasion by soft-rotting bacteria and fungi
Downy mildew on foliage of radish plants (left; center) and cauliflower (right).
Favorable Environmental Conditions
- Cool and wet conditions are conducive for the development of downy mildew
- Greater than 98% relative humidity
- Temperatures between 46-60°F
Often Confused With
- Rhizoctonia on turnip and radish
- White rust
Scouting Notes
- During and after long periods of cool, wet weather, check the undersides of leaves for white mycelial growth.
- Leaves that become severely chlorotic after periods of favorable weather could also be another indicator of downy mildew infection.
Downy mildew on mustard greens