Downy Mildew on Basil
Yellowing along leaf veins, black spots and fuzzy gray growth on basil may mean downy mildew has infected the plants.
This fungal disease is carried on seeds, infected transplants and diseased leaves. It rapidly spreads from infected to healthy plants during damp weather or by overhead irrigation.
Reduce the risk by growing basil in sunny locations with plenty of room to grow into their mature size. The extra space allows sunlight to reach all parts of the plants and the added air movement quickly dries the leaves.
Avoid overhead irrigation whenever possible. Instead, use soaker hoses, drip irrigation or a watering wand that allows you to apply the water directly to the soil.
Remove and destroy infected leaves as soon as they are discovered. Remove and destroy infected plants at the end of the harvest season.
A bit more information: Sweet basil tends to be more susceptible than the red leaf, Thai and other more exotic types of basil. Growing less susceptible types, purchasing healthy plants and changing the location of your basil plantings each year will help reduce the risk of downy mildew. For more information, click here.