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Bacterial Leaf Spot on Melons


Recently I received a call from a grower about the fungicide spray schedule for his melons. He was concerned about higher fungal disease pressure based on the weather for the past two weeks. His concern was valid considering fungal diseases do well in cool wet conditions!

According to Dr. Langston, extension vegetable pathologist, fungal and ‘fungal like’ diseases are more of an issue later in the season than now. But, bacterial spot, caused by Pseudomonas spp., can be a issue this time of year. Especially with the conditions we have had recently.

Today, April 23rd, bacterial leaf spot was found on watermelon and cantaloupe. Both cases warranted an application of copper fungicide.

Dr. Langston says:

“We are seeing Pseudomonas leaf spot on cucurbits again this year, especially after the cool, wet weekend we just had.  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. Usually the weather turns this disease around as warm (80o F+) dry conditions are unfavorable for the bacterium.”

If you’re concerned about bacterial spot on your vegetables apply a low rate of copper fungicide along with the fungicides recommended in the spray schedule. Do not use a high rate given that melons, especially cantaloupes, may be sensitive.
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