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What's Bugging Your Garden? Cucumber Beetles

Updated April 03, 2019
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David Graper

Professor Emeritus of Horticulture Science

garden plants with several large holes in thier leaves.
Striped cucumber beetle damage to plants.

Gardening has been a challenge the last few years what with the record rainfall two years ago, record drought last year and now a wet, cool and late spring. The veggies in my garden are finally starting to grow now that it has warmed up and dried out, at least for a few days. If this spring’s weather wasn’t enough, now the insects are making their own appearance.

The worst insect pest I have in my garden this week are striped cucumber beetles. These little voracious eaters must have been waiting for my squash, pumpkins and melons to emerge from the soil because they have done a lot of damage in a short time.

Pest Profile

several yellow and black striped beetles feeding on plant leaves
Striped cucumber beetles feeding.

Striped cucumber beetles are little yellow and black striped beetles that are fairly small, only about ¼” long, but what they lack in size they make up for in numbers and appetite. My poor little seedlings were hardly out of the soil and just beginning to get their first true leaf when they attacked. Some of the seedlings are completely gone while others are mere skeletons of their former self. But, eating the seedlings is just the beginning.

Associated Diseases

Cucumber beetles are carriers of bacterial wilt, a common disease of cucurbits. The bacteria are in the beetles and get transferred to the plants when they feed on them. So, even if you get rid of the beetles, which is no small feat, bacterial wilt can show up just about the time the plants begin flowering and fruiting later in the summer. The disease causes the vascular tissue to get plugged up with the bacteria which shuts down water transport to the plants so that the whole plant can wilt in a few days. There is no treatment for the disease, once the plants get it so it is a good idea to try to control the beetles to prevent them from spreading the disease.

Lifecycle

There are usually two generations of cucumber beetles in our area. Right now the first generation of beetles is out feeding on the young plants. These beetles overwintered in the soil and have now emerged to eat and make new baby beetles. They lay their eggs in the soil near cucurbit plants so that when the next generation emerges in mid to late summer they will have a ready food source. The second generation will feed on the then larger plants and even on the fruit, particularly in the fall after a frost has taken out the foliage. The fruit damage can mean that the fruit will not store well because the feeding damage will allow for bacterial and fungal pathogens to enter the fruit.

Management Tips

Here are a few tips to try in combating these nasty little pests.

  • First, clean harvest and clean up debris in the fall of the year. If you can do some deep cultivation that will also help the under-ground plant debris to break down and not act as a food source for the larvae. This will reduce the number of beetles that survive and overwinter in your garden.
  • Secondly, delay planting so that the first generation either starves or moves on to other plants before your seedlings emerge. Apply mulch after planting to cover the soil and make it more difficult for the adults to lay the eggs on the soil surface.
  • Floating row covers can also help to keep the beetles away from your young plants. But, you need to be careful that you don’t rap the emerging beetles inside with your plants. You also have to be prepared for wind which can make a mess of your floating row covers and consequently your plants.
  • Some people will put out yellow sticky trap cards on wooden stakes, a few inches above the ground. The beetles are attracted to the yellow color and get stuck on the cards. If you do a search on the internet you will likely find a variety of other home-made remedies that you could try.

Insecticides

There are of course some insecticides that can be used. The standard would be Seven dust, but like potato beetles, these pesky pests have likely developed resistance to this old standby. While a dust formulation can work well, the ideal treatment will be one that you can get on both the upper and lower leaf surfaces. Cucumber beetles are pretty active little guys that will hide under the leaves or in the soil if disturbed. Liquid treatments with insecticides like Imidicloprid, Permethrin and Pyrethrin might work but the adults are rather difficult to kill. Whichever insecticide you decide to try, do your best to get thorough coverage of the plants.