Wilt diseases occur when a pathogen plugs a plant’s water transport system. Bacterial wilt of vine crops is caused by a bacterium, a pathogen so small that thousands can be found in bacterial exudate the size of a drop of water. Even so, the pathogen can multiply quickly and plug the vascular tissues. When this happens, water transport does not occur, and growers report that their plants suddenly wilt and die. This tiny bacterium is transported from plant to plant by the striped and spotted cucumber beetles.
Cucumbers and muskmelons (or cantaloupes) are the major hosts of bacterial wilt, and this is where we see the most damage. The disease can also occur on pumpkins, squash, and rarely watermelon, although it is usually not as severe. Wilt symptoms appear first on individual leaves but quickly spread to lateral shoots; finally, the entire plant wilts. Symptoms develop more quickly on younger, smaller plants.
There is a “quick-and-dirty” field test for this disease. To confirm the presence of bacterial wilt, cut a live, wilted runner off the plant near the crown. You only need the 5 or 6 inches of stem nearest the crown. Cut the stem section in two, hold the cut ends so that they are back together, and squeeze them until the plant sap flows out from each cut edge and the sap intermingles. Then slowly pull the cut ends apart. If there is a strand of sticky sap between the cut ends, a bacterium is probably present and bacterial wilt is a strong possibility. Unfortunately, after you confirm the presence of this disease, there is nothing you can do to stop it in the infected plant. This knowledge should help you control the disease next year.
The primary method for controlling bacterial wilt is to control the beetle vector, the striped and spotted cucumber beetles. The beetles overwinter as adults, and they are present when the vine crops emerge. Because the beetles are most attracted to plants in the cotyledon stage, insecticides should be initiated immediately after planting. Apply insecticides late in the day when blossoming begins so as not to interfere with pollination by bees. Both a preplant systemic and a postemergence protectant insecticide may be necessary to prevent a problem with bacterial wilt in commercial plantings. Commercial growers find that treatment with Furadan at planting time gives moderate control for three to four weeks, but supplemental insecticide use is also necessary. Home growers usually spray plants with an insecticide weekly from the time plants break the soil (or when they are transplanted) until they are in bloom. Chemical options are listed in the homeowner and commercial pest control handbooks. Consult RPD No. 905 for details about bacterial wilt.