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Bacterial Wilt of Cucurbits

This disease is caused by a pathogen so small that hundreds can be found in bacterial exudate the size of a drop of water. The pathogen can quickly multiply and plug the vascular tissues so that water transport does not occur. This tiny bacterium is transported from plant to plant by both striped and spotted cucumber beetles.

Bacterial wilt is most devastating on cucumbers and muskmelons (cantaloupes). The disease can also occur on pumpkins and squash, although not often as severely. It rarely infects watermelon. In all cases, wilt symptoms appear first on individual leaves and quickly spread to lateral shoots, causing the entire plant to wilt. Symptoms develop more quickly on younger, smaller plants.

To confirm the presence of bacterial wilt, cut a live, wilted runner off the plant. (Take the five or six inches of stem nearest the crown.) Cut the stem section in two, then hold the cut ends back together and squeeze them until the plant sap flows out and intermingles from each cut edge. Slowly pull the cut ends apart. If there is a strand of sticky sap between the cut ends, then a bacterium is likely present and bacterial wilt is a strong possibility. Unfortunately, once you confirm this disease, nothing can stop it in the infected plant. However, steps can be taken to prevent the wilt in next year's plants.

The primary method for controlling bacterial wilt is to control the beetle vector. The beetles overwinter as adults that are present when the vine crops emerge. The application of both preplant systemic and postemergence protectant insecticides might be necessary to prevent a problem with bacterial wilt in commercial plantings. Because the beetles are most attracted to plants in the cotyledon stage, insecticides should be initiated immediately after planting. Entomologists warn that when blossoming begins, insecticides should be applied late in the day so as not to interfere with pollination by bees. Consult Report on Plant Diseases No. 905 for details about bacterial wilt.

Author: Nancy Pataky


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