Symptoms
Plants infected with bacterial wilt show a distinct flagging, or wilting, of lateral and individual leaves even when provided with adequate moisture (Figure 1). Cucumber and melon leaves may turn a dull green while squash and pumpkin leaves turn a dull grayish-green and later darken to bronze. Leaves eventually shrivel and die. Infected vines at first appear soft and pale, but later dry.

Affected plants wilt when bacteria and bacterial "ooze" block the flow of water through the plant. The presence of bacterial wilt may be detected by looking for this ooze. When infected stems are cut and their ends squeezed, a milky, sticky bacterial ooze may be observed. In addition, when these cut ends are brought together, and then separated, a "string" of the bacterial ooze may be observed between the two cut ends (Figure 2). Another way to detect the presence of bacterial wilt is to place a cut end of an infected stem in a glass of water. The bacterial ooze may be seen flowing into the water. Although simple, these tests for the presence of bacterial wilt are not always adequate, and should not be depended on for positive diagnosis.

The squash vine borer insect can also cause wilting of squash, pumpkin or watermelon. It is important to determine the cause for wilting since management techniques differ based on the causal organism. See the Yard and Garden Brief Squash Vine Borer Management in Home Gardens, for more information on this insect.

Disease Cycle
The bacteria causing this disease cannot survive in dry, infected plant material for more than a few weeks. Instead, the bacteria survive the winter in the gut of adult striped or spotted cucumber beetles (Figures 3,4). When these beetles feed on young cucurbits in the spring, they create small holes in the leaves. The bacteria may be deposited on the leaves through beetle feces, and may enter a susceptible host through the beetle feeding wounds. Once inside a host plant, the bacteria reproduce and produce gums that block the vascular system. Cucumber beetles may also carry the bacteria on their mouthparts and spread the bacteria by feeding on infected, then non-infected plants.

Management
Once a plant is infected with bacterial wilt, no control of the pathogen is possible. Infected plants should be removed and destroyed without injuring nearby plants. The best control for this disease is achieved by managing the beetle vector of the pathogen. As with any disease, no single management practice should be relied upon for control; rather, a combination of management practices will provide the best control.

• Use resistant varieties when available. Watermelon in general is not as susceptible to bacterial wilt as other cucurbits. The cucumber varieties County Fair, H 19 Little Leaf, and Saladin tolerate bacterial wilt.
• Do not plant cucurbits near weedy woods or brush where cucumber beetles are more likely to overwinter.
• Plants may be covered with row covers such as cheesecloth to prevent cucumber beetle feeding. Row covers should be placed over the plants as early in the season as possible and must extend to the soil surface to prevent beetle entrance. Row covers must be removed when the plants flower to allow for pollination.
• Yellow sticky cup traps placed every 20 feet along the row will help trap the cucumber beetles. Replace when the traps become dusty and are no longer sticky.
• Remove all infested vines to prevent further spread of the disease. The removal of vines at the end of the season will also decrease the overwintering sites of the cucumber beetle.
• There are several insecticides that are labeled for cucumber beetle control. Look for insecticides that contain the active ingredient permethrin (Eight) or carbaryl (Sevin). Be sure that the chemical you use is labeled for use on your plants since cucurbits are sensitive to many chemicals. In addition, if you choose to spray carbaryl, spray late in the day when bees are less active to prevent unintentional bee mortality. Organic control options include rotenone 1% dust, foliar applications of kaolin clay (Surround WP), and insecticidal soap containing neem oil. Remember to follow all label recommendations. Control of the beetles should take place as early in the season as possible since cucumber beetles prefer to feed on young cucurbits and this is when the plants are the most susceptible to bacterial wilt.

Options for Managing Bacterial Wilt Affecting Cucurbit Crops, Cornell University Vegetable MD Online Striped Cucumber Beetle, E. C. Burkness and W. D. Hutchison, University of Minnesota Department of Entomology

P260C
11/02