WESLACO — “I don’t think people in general realize what growers go through to put food on all our tables,” said Lynn Brandenberger, a vegetable specialist at the Texas A&M Agricultural Research and Extension Center in Weslaco.
“Once you understand plant diseases and how quickly they can kill a crop without warning, you gain a healthy respect for growers because so much can go wrong.”
Brandenberger made that comment while looking over a watermelon research field plot at the Weslaco center. Until two weeks ago, this watermelon variety trial looked healthy and vigorous. Suddenly, something went terribly wrong and the plants’ vines took a nosedive. Leaves wilted, the fruit was left exposed to burning heat and sun, and without recourse, the plots suffered major crop damage.
Ironically, Brandenberger was glad to see this disease in his variety trials. He will now be able to evaluate all 38 different varieties of watermelon for their resistance to the disease, commonly known as vine decline. It is caused by a fungus called Monosporascus cannonballus. After harvesting the melons from his relatively small research field plot and tabulating the results in the coming weeks, he’ll be able to pass that invaluable information on to growers. Similar watermelon tests are being conducted by Texas A&M at four other locations throughout the state.
“We’ll rate the 38 different watermelon varieties on a whole range of criteria ranging from yield and fruit quality to resistance to vine decline and powdery mildew. But with the severe disease pressures we’re seeing here in our research plots, we’ll be able to observe all these watermelon varieties under much more extreme conditions,” he said, “which should make for some very valuable information for growers.”
Unfortunately, vine decline is not limited to research field plots. Brandenberger says Valley commercial growers have seen a lot of the disease this year in cantaloupes, honeydews, and watermelon.
“Vine decline is a fungal disease that persists in the soil for several years and does well on all sorts of cucurbits,” he said. “It also seems to do well in hot, arid climates like we have here and in southern New Mexico and southern Arizona. In fact, because vine decline has been so persistent here for several years now, it was the driving force behind setting up these variety trials in South Texas.”
Commercial harvesting of the Valley’s 15,000 acre melon crop valued at some $50 million, is more than half completed, Brandenberger said, and because vine decline tends to show up during the latter fruit-maturing stage of melons, the disease will likely continue to plague Valley growers this year.
For now, the only recommendations for growers to avoid vine decline are preventative in nature: rotate crops and study variety trial results to achieve the highest possible level of tolerance.
Dr. Marvin Miller, a vegetable plant pathologist at the A&M center in Weslaco, currently heads a group of scientists conducting various aspects of agricultural research to combat the disease.
Known as the Melon Working Group, the scientists are investigating chemical control, biocontrol and plant tolerance or resistance.
In studies not yet completed, Dr. Miller has identified several fumigants that are effective in preventing vine decline when used as a soil treatment prior to planting. Until exhaustive tests are completed, however, these products are not yet available for use on melons.
“Vine decline is a very vigorous and persistent disease that, unfortunately, will take several more years of research to effectively control,” he said. “Until then, growers need to take whatever precautions they can and hope for the best.”
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