Watermelon Disease, Update from UGA

This was in my inbox today. We have had similar reports in Florida, throughout the Suwannee Valley as well as in the Tri-County Agricultural Area. Still cool and wet here.  Thanks to Dr. David Langston, Associate Professor of Plant Pathology, and  Matt Roberts at UGA Colquitt County Extension for the update.

1.      Some of you may be experiencing some problems with Pseudomonas leaf spot. I’ve been watching this develop over the last week and I was hoping the weather would warm up and dry up.  The current forecast indicates cool, wet weather.  This Pseudomonas leaf spot causes just that, a leaf spot.  The spots can appear dark and greasy at first, then they turn light tan in the center and you can see a concentric ring pattern in the lesion.  I see a little bit every year, but not as much as we have seen this year.  Why are we seeing so much this year?  The spring has been exceptionally cool and wet, and it looks to stay that way.   What do you do about it?  Usually nothing but wait till warmer temperatures come along.  Bacterial diseases caused by most Pseudomonads are cool weather diseases.  Lately I have been recommending copper sprays to reduce the spread of this disease. I’d use the lowest rate of whichever copper brand you use and use it on a 7 day schedule until the temperatures get warmer and stay warmer. 
2.      There have been more severe outbreaks this year of Fusarium wilt. This is another disease that is favored by cool, wet conditions.  Right now we are getting in several samples from fields.  This is a disease of younger plants and symptoms appear as wilted runners, that may have discolored vascular tissue when cut.  There are no visible lesions, cankers, or spots that you will see with other diseases.  Usually we see this disease on seedless watermelon, but we are seeing more and more on seeded varieties. Once the disease is observed in the field, no remedial control measures are available to use.  Rotation away from infested fields, using resistant varieties, and delaying planting will be somewhat effective for subsequent crops.  Next year we may have some at-plant fungicides registered for use on this disease.

Matthew J. Roberts

A&NR County Extension Agent
Colquitt County Extension

Leave a Reply

Your email address will not be published. Required fields are marked *