Downy mildew is a plant disease caused by parasitic organisms more closely related to algae than fungi. It primarily affects leaves, stems, and fruit, causing stunted growth, yellowing, and wilting. It requires water and cooler temperatures to survive and is most commonly found in plants during the spring. Downy mildew is more difficult to control and prevent than powdery mildew and can require frequent application of fungicides during the growing season.
How to Manage Downey Mildew in Home Garden
Disease Cycle of Downey Mildew
- The disease cycle of downy mildew begins in the soil, where oomycete spores are windblown or splashed onto nearby plants.
- The spores latch onto the underside of leaves and penetrate the leaf’s surface with their mycelia, causing downy growth and spotting on the upper side of leaves.
- A mat of sporangia forms underneath the leaf, which releases more spores. These spores can colonize other plants if conditions are right and can also be dispersed into the soil via rotting plant debris, where they can survive up to five years.
- The mildew’s mycelia spread throughout the plant’s stems, potentially infecting new growth. Infected plants may produce damaged fruit or have problems with new growth.
Causes of Downey mildew
- Parasitic organisms from the Peronospora or Plasmopara genus cause downy mildew.
- These organisms are more closely related to algae than fungi and require water to survive and spread.
- They are spread from plant to plant by airborne spores and are favored by wet weather conditions with prolonged leaf wetness.
- Cool temperatures also promote the growth and spread of downy mildew.
Garden Plants Which are affected by Downey Mildew
- Annuals: snapdragon, Salvia, alyssum, pansy, sunflower, Impatiens walleriana, coleus, statice, Verbena, ornamental cabbage, and basil
- Perennials: Aster, Buddleia, Coreopsis, Geranium (not Pelargonium), Geum, Gerbera, Lamium, Delphinium, Veronica, and Viola
- Vegetables: cucumbers, squash, melons, and spinach
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Symptoms of Downey Mildew Attack on Home Garden
- The initial symptoms include yellow to tan angular lesions that can appear at the center of the plant’s leaves and then spread between the small leaf veins.
- The spots enlarge and turn brown with a fine gray to purplish mold forming on the underside of the leaves during wet weather.
- The affected leaves may also become distorted, and the plant may develop stunted growth. As the disease progresses, it can quickly kill leaves and entire plants, especially during warm, wet weather.
- The damage can lead to reduced yields or complete crop loss if the disease is untreated.
Cultural Management of Downey Mildew in Home Garden
- Cultural management is an important component in managing downy mildew in home gardens. This includes removing and disposing of affected leaves a