How to Prevent Bacterial Wilt in Cucumbers

Cucumber vines that mysteriously wilt and cucumber plants dying overnight means they are probably infected with bacterial wilt. The cucumber beetle transmits cucumber bacterial wilt. There’s not much to be done once the vines are infected with bacterial wilt and the cucumber plants are dying, but you can take measures early in the season to protect your young cucumber plants.

Symptoms of Bacterial Wilt

One sign of bacterial wilt is that the plants wilt even when well watered. Test the problem by cutting a badly wilted stem just above soil level and squeezing it. If a sticky, oozy substance comes out, it’s bacterial wilt. This slimy substance clogs the plant’s circulatory system, so it can’t take in water.

The damage from cucumber wilt happens quickly in cucumbers and muskmelons. Within a week of becoming infected, dull patches develop on the leaves. Within two weeks the entire vine wilts, and the fruits will look deformed and small. In many cases, there's no yellowing of the cucumber leaves.

Causes of Bacterial Wilt on Cucumbers

Bacterial wilt is caused by the bacterium Erwinia tracheiphila, which is spread when the striped cucumber beetle or the spotted cucumber beetle feeds on the plant’s leaves. The bacteria can overwinter in the beetle’s digestive system or the insects may pick it up while feeding elsewhere. These beetles also spread the cucumber mosaic virus.

The striped cucumber beetle is about a 1/4-inch long and has three black stripes on its yellow-green wings. The spotted cucumber beetle is a similar yellow-green color but has 12 black spots. Spotted cucumber beetles feed on cucurbits (cucumbers, melons, squash, pumpkins, and gourds) and other plants.

The larvae of both beetles are white with dark heads and posteriors. They are found in the soil under your cucumber plants. The eggs are a bright orange-yellow.

Controlling Cucumber Bacterial Wilt

The best way to prevent bacterial wilt is to keep your plants healthy. Cucumber beetles prefer feeding on wilted plants, which are already more prone to infection. Make sure your plants are well watered and well cared for. The bacteria need a wound, such as from a deep beetle bite or a tear, to enter, so be careful not to damage your cucumber plants. Other tips for controlling bacterial wilt include:

• Choose resistant varieties: Many cucumber varieties were bred to resist the bacteria spread by cucumber beetles. If starting cucumbers from seed, select resistant varieties, or ask for resistant varieties when purchasing cucumber plants at your local nursery or garden center.
• Monitor early: Keeping cucumber beetles out of your garden is the best form of control. The beetles show up in early spring and lay their eggs on the undersides of the leaves. Keep an eye out for signs of the beetles, as soon as your cucumbers are planted. Monitor the leaves and destroy any egg sacks by removing or squashing them. Adult striped cucumber beetles are most active from dusk to dawn.
• Apply barriers: Protect early cucumber plantings by covering the plants with a floating row cover. Secure the bottom of the cover so that beetles won't crawl underneath. Remove the cover as soon as the flowers appear to give pollinators access to the blooms.
• Use pesticides at the larval stage: Adult beetles have a hard carapace, so you will have greater success if you apply pesticides during their larval stage when they are still soft-bodied. Use pyrethrin-based products because they are effective against many soft-bodied insects but have very low toxicity to humans and animals. Keep in mind that the toxins indiscriminately kill pests and beneficial insects, including pollinators, so always use pesticides as a last resort while carefully following the label's directions.