Bacterial wilt, unfortunately, is very common. This destructive disease can causes the complete loss of your cucumber, cantaloupe, squash or pumpkin plants. All before you’ve even had a chance to see one tiny fruit develop.
How do I know if it’s bacterial wilt?
The symptoms start as leaves or groups of leaves wilt. This is followed by entire runners and then whole plants succumbing to the bacteria. Unlike many diseases, the wilting foliage may appear dark green and healthy, except for the wilt. But eventually everything will turn darker and blacken as it dies.
Though not 100% reliable, you can test your cucumbers and cantaloupe plants to see if bacterial wilt is the culprit. Using a sharp knife, conduct a ‘bacterial ooze test.’ Cut through one of the wilted vines near the crown. Once the cut is made, touch the knife to the cut end, slowly pulling the blade away. If bacterial wilt is present, you will see fine threads of bacterial slime as it is drawn out of the cut. This test is not as reliable for pumpkins and squash, due to the structure of the vine itself. For these particular fruits, place cut pieces of stem into a glass of water and the ‘ooze’ will flow into the water.
The other, more obvious, sign is the presence of the spotted or striped cucumber beetle. Or evidence of their feeding. If you are in the habit of checking your vegetable plants regularly, you may see the chewed leaves before you see the beetles. Although any sign of chewing or wilting on your leaves should encourage you to look further. The striped cucumber beetle is about 1/5 inch long, is yellow-green and will have 3 black stripes running the length of the beetle. The spotted cucumber beetle is a little bit larger, about 1/4 inch long, with 3 symmetrical bands of 4 spots each going across the width of the body. The larvae, which feed on the root systems, are cream-colored with dark heads.
What organic measures can you take to protect against bacterial wilt?
- Avoid planting susceptible crops near corn, which the spotted cucumber larvae will also feed on.
- Plant vegetable varieties that are resistant to bacterial wilt.
- Rotate your cucurbits. Beetles will hibernate under leaf clutter and in the soil through the winter. They become active again once temperatures are regularly above 55° F.
- Install row covers early and leave them on late.*
- Remove and destroy any infected plant material. Cucumber beetles can spread the disease from infected to healthy plants.
- Plant trap crops 2 weeks prior to planting your cucumbers or melons. For example, plant Blue Hubbard squash around the perimeter of where you will be planting your cucumbers. This directs the cucumber beetle population to what they like best..
*Studies, specifically at Ohio State University and Iowa State University, have found that leaving the row covers on 10 days longer than normal results in significantly better control. Put the row covers on as you plant or transplant. Most recommendations will say to remove the row covers when flowers appear, but the studies at these universities have found that the first flowers to appear are male, which means they are not necessary for pollination. Wait until the female blossoms appear. This results in better cucumber beetle control. And it doesn’t negatively affect crop yield.
Some growers will opt to use chemical means of control. Application of pyrethrin or carbaryl in April to June, before beetles have a chance to lay eggs, may help. There are also insecticide-bait combinations with both a beetle attractant and a small amount of carbaryl. We, however, do not carry these chemical options due to their negative impact on the environment and the harm they may cause to your family or pets.
Is the squash vine borer the culprit?
Similar symptoms that can affect cucurbit vines are caused by the squash vine borer. Unlike entire groups of leaves or vines wilting, the damage is usually limited to single vines on plants that are otherwise healthy. The squash vine borer is a whitish-colored caterpillar with a brown head and can be found inside the stems of the wilted vines. You may also see a moist, sawdust-looking material around the runners infested by this pest. Cucumbers and melons are not usually first on their list of preferred veggies, though. Squash vine borers will go for squash, zucchini, pumpkins and gourds first; their favorite is Hubbard squash, while they will avoid butternut squash.
If plants other than your cucumbers and cantaloupe are wilting, then the squash vine borer may be the perpetrator, not the cucumber beetle. You can look to this article for ways of controlling or deterring this pest: Invasion of the Squash Vine Borer