Warm temperatures and leaves that stay wet for hours at a time are environmental factor that contribute to foliar diseases. Here are a few common diseases that can injure plants and reduce harvests. Click links for detailed information:
Early blight (Alternaria solani)-
Irregular brown lesions (often with a yellow halo) that enlarge and show a distinct bull’s- eye target pattern.
Septoria leaf spot (Septoria lycopersici)-
Small dark spots enlarge and develop tan centers with dark borders. It’s a fungal disease that often co-occurs with early blight
Manage these diseases by removing badly infected lower leaves (see below), water at the base of each plant and avoid wetting foliage, apply a fixed copper fungicide if the problem is persistent and results in greatly reduced plant growth and yield.
Late blight (Phytophthora infestans)-
One of the most devastating diseases of potato and tomato. The last major outbreak in our region occurred in 2009, although isolated cases are often seen in Western MD where summer temperatures are cooler. This fungal disease is quite different in appearance from early blight and Septoria leaf spot.
Follow confirmed reports of late blight in the U.S. on the usablight website. HGIC and GIEI websites will alert gardeners immediately if we learn of reports in Maryland.
Bacterial leaf spot of peppers has been widely reported and has the potential to reduce plant growth and pepper harvests this summer. Pick off and dispose of badly infected leaves and consider applying a fixed copper liquid fungicide if the symptoms progress.