Abstract
During the summer of 2007, a severe foliar disease was noted on basil grown in southern Florida. The disease was characterized by foliar chlorosis, frequently delineated by leaf veination, with a light gray fungal growth evident on lower leaf surfaces. Initially observed in the lower canopy, the disease subsequently
developed in the mid to upper canopy. Severely infected leaves frequently dehisced. The disorder displayed fungal signs associated with downy mildew. Crop losses in individual fields ran as high as 100%, with a number of basil shipments being rejected at delivery due to symptom development in transit. The performance
of Koch’s postulates has verified the disease as being caused by a fungal species, most likely within the genus Peronospora.