Basil Downy Mildew

If you haven’t yet heard of basil downy mildew, you will. New to U.S. gardens in 2007, the disease has already been confirmed in more than a dozen states. The first sign of trouble is grayish spores on the underside of leaves. But these usually go unnoticed until the disease progresses and yellow splotches appear on the tops of leaves.

New basil varieties that are less susceptible to the disease will no doubt become more widely available over time, so look for those in the future. Until then, if you catch downy mildew early enough (when you spot the spores on the undersides of leaves), you can treat it with fungicides.

High humidity increases the likelihood of infection, so avoid overhead watering and do your best to provide good air circulation. Outbreaks in some states have been traced to basil purchased at big-box stores, so inspect plants carefully before purchase.