Cucumber beetles

Monitoring

• Concentrate your efforts on striped cucumber beetles. It is rare to see spotted cucumber beetles early in the season, and their numbers usually are too low to require treatment.
• Pay attention to plants in the cotyledon and first to third true-leaf stage; high amounts of cucumber beetle feeding can kill young plants.
• Once squash and pumpkin plants have four or more leaves, they can tolerate some cucumber beetle feeding.
• Continue monitoring melons and cucumbers, as their susceptibility to bacterial wilt makes cucumber beetles more important to manage.

Cultural controls

Keeping your garden clean

• Remove weeds in and around your garden because they may be potential hosts for adults.
• If a plant shows signs of bacterial wilt, remove the infested plant before more beetles can feed on the plant and spread the bacterium.
• After the summer ends, remove garden debris and leaf litter to reduce places where adult beetles spend the winter.

Use trap crops

A trap crop is a plant that attracts pests away from your main garden plants. The plants draw pests to themselves and away from the plants you want to harvest.

• Plant a few highly attractive cucurbits, such as blue hubbard squash.
• Plant your trap crop a week or two before you plant the rest of your cucurbits, as the beetles tend to show up in one early-season flush.
• Once striped cucumber beetle numbers build up in the trap crop, treat them with an effective pesticide.

Physical controls

• Once plants are established, placing thick straw around the base of the plants can make it harder for cucumber beetles to lay their eggs.
• If you have just a few plants in your garden, you can physically remove the beetles by swatting them into a bucket of soapy water.
• You can protect your cucurbits by using a floating row cover or a similar barrier during early to mid-June to keep the striped cucumber beetles from reaching plants.
  • Remove it when plants start flowering. Most plants in the cucurbit family require insect pollination, and row covers prevent pollinators from reaching the flowers.

Using pesticides

Use pesticides only when necessary.

Watch your plants regularly for striped cucumber beetles when new leaves emerge from seed leaves. If you find two or more beetles per plant on 25% of your plants in the cotyledon stage, apply a pesticide.

• Once beetles are present, monitor more frequently (every few days).
• Once plants are at the second or third true-leaf stage, check the defoliation level.
  • Monitoring the defoliation level is much faster and still allows for the detection of bacterial wilt.
• If you find 25% of a given plant defoliated, apply pesticides.

Striped cucumber beetles seen later in the summer can be ignored as they cause little or no damage.

There are many products available. Read the label to determine whether it works on cucumber beetles, whether it can be used on the plant you wish to treat, and how to use the product safely and effectively.

The following information is specific to fruit farms and those growing fruit for commercial sale or use.

Monitoring for cucumber beetles

• Scout at least weekly, increasing frequency once you find beetles.
• Concentrate your efforts on striped cucumber beetles. It is rare to see spotted cucumber beetles early in the season, and their numbers usually are too low to require treatment.
• Pay attention to plants in the cotyledon and first to third true-leaf stage; high amounts of cucumber beetle feeding can kill young plants.
• Once squash and pumpkin plants have four or more leaves, they can tolerate some cucumber beetle feeding.
• Continue monitoring melons and cucumbers, as their susceptibility to bacterial wilt makes cucumber beetles more important to manage.

Cultural controls

• Removing or destroying crop residue will reduce potential overwintering areas.
• Crop rotation will make exclusion efforts more effective.

Physical controls

Exclusion

• In the field, floating row covers can be placed as seedlings emerge and plants start to grow. Remove row covers when plants begin to flower so pollination can occur.
• In the hoop house or greenhouse, insect exclusion screens can keep cucumber beetles out. A screen size of 0.8 x 1.0 mm can keep beetles out while allowing ventilation.

Trap crops

• Trap crops, or cucurbit cultivars that are highly attractive to pests, can be used to reduce feeding on the crops you actually want to harvest.
• Blue Hubbard squash is a common trap crop variety for cucumber beetles.
• Plant your trap crop two weeks earlier than your main crop, as this will attract early-emerging cucumber beetles.
• Trap crops can be treated with insecticide to prevent beetles from migrating to crops.

Kaolin clay

• Kaolin clay can deter beetle feeding. It is best used before you see major feeding.

Chemical controls

Thresholds

• Vine crops are most susceptible to cucumber beetle feeding when they are in the 1-3 leaf stage. Those that are susceptible to bacterial wilt then remain at risk all season long.
• For pumpkins and squash, use a threshold of 0.5 to 1 beetle per seedling. Once plants have 2 or more true leaves, Minnesota research suggests that treatment should be considered once beetles have defoliated 25% of leaves.
• For cucumbers and melons that are susceptible to bacterial wilt, use a threshold of 0.5 beetles per plant for seedlings and 1 per plant for older plants.

Seed treatments

• Seed treatments effectively protect young plants in the first few weeks of life. However, consider whether a seed treatment is truly necessary.
• Seed treatments offer 2-3 weeks of protection; if you hold the transplants indoors longer than that, the seed treatment will not be effective once the plants are outside.

Application timing

• Make applications before 8 a.m. or after 6 p.m., as bees are most active in the morning, and squash flowers close later in the day.
• See the Midwest Vegetable Production Guide for options. Remember to rotate chemistries to manage potential resistance issues.