Bacterial Wilt of Cucurbits

Bacterial wilt of cucurbit crops is a common issue for homeowners and commercial producers in Kentucky. Cucumbers and muskmelon (cantaloupe) are highly susceptible to bacterial wilt, while squash and pumpkin are less susceptible. Watermelon is known to be resistant to bacterial wilt. Infected plants quickly collapse, resulting in crop loss. Preventative practices are critical for avoiding yield loss.

Bacterial Wilt Facts

• Symptoms often first appear as dull green, wilted leaves or groups of leaves (Figure 1). Over time, wilting becomes prominent throughout the plant; collapsed foliage and vines turn brown, shrivel, and die (Figure 2).
• Field diagnosis can be conducted using a simple “bacterial ooze test.” For cucumber and muskmelon, select a wilted vine (not dead), and using a sharp knife, make a cut near the crown. Touch the cut ends together for 3 to 5 seconds and then slowly pull them apart, looking for fine thread-like strands of bacterial ooze connecting the two parts (Figure 3). To diagnose bacterial wilt in all cucurbits, including squash and pumpkin, place cut pieces of affected vines into a clear glass container filled with water. When the bacterium is present, a cloudy string or mass of bacterial ooze will flow into the water from cut stem pieces (Figure 4).
• Striped and spotted cucumber beetles transmit the bacterial pathogen during feeding (Figure 5). The pathogen overwinters in the gut of these vectors.
• Spring temperatures above 55°F promote growth of cucurbit seedlings, as well as striped and spotted cucumber beetle feeding on all plant parts.
• Bacterial wilt is caused by the bacterial pathogen Erwinia tracheiphila.

Figure 1: Initial symptoms include dull green, wilted leaves. (Photo: William Nesmith, UK)

Figure 2: Infected plants eventually collapse with vines becoming brown and shriveled. (Photo: Edward Sikora, Auburn University, Bugwood.org)

Figure 3: In cucumber and muskmelon, diagnosis in the field can be conducted by cutting a wilted vine, touching the two end together, pulling them apart, and looking for the presence of thread-link strands connecting the pieces. (Photo: Gerald Holmes, California Polytechnic State University at San Luis Obispo, Bugwood.org)

Figure 4: Diagnosis of bacterial wilt in cucurbits, including squash and pumpkins, can be achieved by placing a cut stem in water inside of a glass jar. The appearance of a cloudy mass or string indicates presence of the bacterium. (Photo: Bruce Watt, University of Maine, Bugwood.org)

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Management

Once plants become infected with bacterial wilt, no disease management practices are effective. Preventative strategies should be used to limit introductions and spread of disease.

Figure 5: Striped (left) and spotted (right) cucumber beetles transmit bacterial wilt during feeding. (Photo: Ric Bessin, UK)

• Select resistant or tolerant cultivars.
• Rotate crops away from cucurbits for a minimum of 2 years.
• Manage weeds.
• An insecticide management program should be implemented as soon as seedlings emerge or after transplanting. An effective program should include one or more of the following.
  • Contact or systemic insecticides
  • Trap cropping 
  • Physical barriers (netting) and mulches
• Remove and destroy infected plants.

Commercial growers can find information on insecticides in the Vegetable Production Guide for Commercial Growers (ID-36) and the Southeastern U.S. Vegetable Crop Handbook (SEVEW). Homeowners should consult Home Vegetable Gardening (ID-128) for insecticide information or contact a county Extension agent for additional information and recommendations regarding insecticides.   

Additional Resources

• Bacterial Wilt of Cucurbits (PPFS-VG-11)
• Cucumber Beetles (ENTFACT-311)
• IPM Scouting Guide for Common Pests of Cucurbit Crops in Kentucky (ID-91)
• Sustainable Disease Management of Cucurbit Crops in the Home Garden (PPFS-VG-19)
• Home Vegetable Gardening (ID-128)
• Vegetable Production Guide for Commercial Growers (ID-36)
• Southeastern U.S. Vegetable Crop Handbook (SEVEW)

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By: Kim Leonberger, Plant Pathology Extension Associate, and Nicole Gauthier, Plant Pathology Extension Specialist

 

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