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H. F. Schwartz, Colorado State University, Bugwood.org
Bacterial wilt is caused by the bacterium Erwinia tracheiphila. This pathogen can cause severe losses in cucumbers and muskmelons; squash and pumpkins are less severely affected. Watermelon is not affected. Bacterial wilt does not occur every year in Minnesota.
- Leaves first appear dull green, wilt during the day, and recover at night.
- Leaves eventually yellow and brown at the margins, completely wither and die.
- Wilt progression varies by crop. Cucumbers and melons wilt and die rapidly. Pumpkins take up to 2 weeks to completely wilt. Summer squash may continue to produce several for several weeks even when infected.
- Wilt progresses down the vine until entire vine is wilted or killed.
- Striped or spotted cucumber beetles will be present in the garden.
- If infected vines are cut close to the crown of the plant and the cross sections pressed together, thread like strands of bacterial ooze can be seen when the two halves are gently pulled apart again.
C. Averre, NCSU Bugwood.org
The bacteria overwinter in the gut of the striped and spotted cucumber beetles. Not all beetles carry the bacteria. Beetles that feed on infected plants pick up the bacteria. They then move to new plants, creating wounds through feeding. The bacteria are on the mouth parts or in the fecal matter of the beetle and enter the plant through the feeding wounds.
The bacteria multiply rapidly within the plant and plug the vascular tissue resulting in wilting of the vines. Once a plant is infected with bacterial wilt, there is no way to control the disease. The bacteria cannot be transmitted in seed, do not survive in soil, and only survives in plant debris for a short period of time. It cannot overwinter in Minnesota in plant debris.
- Managing cucumber beetles provides the most effective control of bacterial wilt.
- If disease appears in a few plants, rogue and bury these plants to prevent further spread of the disease.
- Pesticides will not help in managing a cucurbit plant infected with this bacterial disease.