Cucumber vines that mysteriously wilt and die off are probably infected with bacterial wilt. Cucumber bacterial wilt is transmitted by the cucumber beetle. There’s not much you can do once the vines are infected with bacterial wilt, but you can take some measures early in the season to protect your young cucumber plants.
Symptoms of Bacterial Wilt
One sign of bacterial wilt is the plants wilting even when they’ve been well watered. You can also test cucumbers 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 the water it needs.
The damage from cucumber wilt happens quickly in cucumbers and muskmelons. Within a week of infection, you may start to see dull patches on the leaves. Within two weeks, the entire vine will be wilting and the fruits will look deformed and small. In many cases, there's no yellowing of 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 can 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 and can be 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, and wilted plants 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 through, so be careful not to damage your cucumber plants. Other tips for controlling bacterial wilt include:
- Choose resistant varieties: Many cucumber varieties relatively tolerant of the bacteria spread by cucumber beetles are available on the market. Check seed packets or ask your nursery specialist to find out the best ones for your area.
- 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.
- Apply barriers: You can protect early cucumber plantings by covering the plants with a floating row cover or cheesecloth. Secure the bottom of the cover so that beetles won't crawl underneath. Remember to remove the cover when the flowers appear to give pollinators access to the blooms.
- Consider pesticides: Cucumbers are very sensitive to pesticides, so use them as a last resort and follow the label directions carefully. Striped cucumber beetles are most active from dusk to dawn; spraying in the evening is most effective. Use sprays containing pyrethrins since this a plant based deterrent and more organically sound. Adult beetles have a hard carapace, so you will have greater success if you spray these pests during their larval stage when they are still somewhat soft bodied.
Unfortunately, if your vines become infected, they will need to be pulled and removed. There's no cure for bacterial wilt. Remove all the vines in the fall.