Bacterial Wilt of Cucumber
Click for larger image Collapsed cucumber plant (Cucumis) caused by bacterial wilt

Cucumber bacterial wilt is caused by the bacterium, Erwinia tracheiphila, and is characterized initially by wilting and drying of individual leaves, especially those exhibiting cucumber beetle injury. Cucumbers and muskmelons are more susceptible than pumpkins or squash; the disease is rarely a problem on watermelons.

Symptoms and Diagnosis

Infected plants initially show wilting and drying of individual leaves. As the leaves wilt and shrivel, stems may dry out suddenly. Later, wilting spreads to entire branches and vines. Wilting will occur during the middle of the day during periods with high water stress. The vine may recover at night. Eventually, however, the entire vine will wither, collapse, and die. In partially resistant plants, symptoms appear as dwarfing, excessive blooms, and branching. A good diagnostic test for this wilt is to cut a wilted stem near the base. Touch a knife blade to the cut and draw away from the cut. White to clear strings of the bacterial ooze will be strung out from the cut made on the infected plant to the knife blade. This diagnostic test is not 100% reliable. Further investigation may be necessary.

Life Cycle

The bacteria overwinter in the digestive system of the cucumber beetle. In the spring, bacterial wilt is spread from plant to plant through both the striped and spotted cucumber beetles that feed on cucumbers and other relatives of this family. The bacteria are released through the insect excrement and move into host plants through the stomates and wounds, most likely the ones made when the insects feed. Insects ingest more bacteria as they feed on infected plants, and the cycle is repeated.

Integrated Pest Management Strategies

1. Protect plants with netting. Prevent cucumber beetles from feeding and infecting plants by covering them with netting or porous fabric.

2. Remove and destroy plant material when symptoms of wilting are first noticed. There are no cures for the disease. Beetles spread the bacterium from infected plants to healthy plants.

3. Grow susceptible crops on rotation every third year. Since beetles overwinter in the soil and carry the bacterium, the cycle can be disrupted by only planting the host in an area every third year.

4. Avoid planting cucurbits next to corn. Spotted cucumber larvae also feed on corn; avoiding close plantings of these two crops may help control the beetles on cucurbits.

5. Grow varieties that tolerate bacterial wilt like butternut or acorn squash and Saladin or County Fair 83 cucumbers. No muskmelon varieties are known to be tolerant to bacterial wilt.

6. Dust plants with insecticide in the spring before the cucumber beetles have a chance to lay eggs (April-June). Apply pyrethrin or carbaryl (Sevin). Try an insecticide-bait combination such as Adios that has cucurbitacin, the beetle attractant, and a small amount of carbaryl (Sevin).

Organic Strategies

Strategies 1, 2, 3, 4, and 5 are organic approaches.

More images:

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Collapsed cucumber plant (Cucumis) due to bacterial wilt
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Bacterial wilt of cucumber begins with the wilting and drying of individual leaves as on this cucumber plant (Cucumis)
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Bacterial wilt of cucumber beginning on a cucumber plant (Cucumis)
 
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