Photo and article: Joan Allen, UConn Extension

Basil downy mildew, a damaging disease of sweet basil plants, has been confirmed on plants at big box store garden centers (non-locally grown plants) in the Northeast. The major symptom is yellowing of the leaves, often between the veins.  Dark, sooty-looking spores of the fungus-like pathogen (Peronospora belbahrii) are produced on the leaf undersides. These are spread to other plants by wind and splashing rain. Whether or not you purchased your sweet basil plants at one of these retail outlets, it’s important to keep an eye out for it on your garden basil because it spreads easily during damp weather. Plants can be protected by promoting good air flow around them for rapid drying. Do this by spacing plants generously, avoiding overhead irrigation, and controlling weeds near them.  Preventive fungicides are available but once plants are infected they should be removed.  Healthy looking leaves from infected plants can safely be used. For more information refer to the UConn fact sheet or contact the UConn Home and Garden Education Center at 877-486-6271 or ladybug@uconn.edu