Current Disease Problems

David B. Langston, Jr.
Extension Plant Pathologist - Vegetables
University of Georgia

The continuous rainy weather has caused several complications for vegetable diseases. Bacterial diseases in onions have been causing severe problems for many growers. We have been isolating primarily bacterial streak (Pseudomonas viridiflava) but have also seen some caused by Pseudomonas marginalis. Copper and mancozeb tank- mixes are the only remedial controls for bacterial pathogens on any crop at this time. Good coverage and short intervals (5 - 7 days) are essential for copper sprays to work properly. Warm, dry weather would help more than anything else to suppress bacterial disease spread.

Gummy stem blight of watermelon has been reported from several greenhouses across the state. This fungus will cause round lesions on leaves that have concentric ring patterns within the lesions. The warm, overcast, damp conditions favor the deveopment and spread of gummy stem blight in greenhouses. The most effective way to deal with this disease is to ensure good air circulation to cut down on humidity and use chlorothalonil products every 5 - 7 days. Ideally, the best way to avoid damage from gummy stem in the field is to obtain disease free transplants if possible.

Last but certainly not least, we have detected fruit blotch from one greenhouse within the past week. The disease was first detected in the 'Genesis' variety but since then we have seen it show up on other varieties in the same greenhouse. To be on the safe side I would check 'Genesis' transplants very carefully. Copper tank-mixed with mancozeb has been very effective in suppressing fruit blotch, but, as with gummy stem, the preferred method of action is to obtain disease- free plants.

March 2003