Cucumber Beetle

Cucumber Beetle

Whether striped or spotted, this voracious garden pest can cause serious damage to cucurbit crops. Here’s how to identify and effectively control cucumber beetles using safe, organic methods.

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Cucumber beetles are found across the United States, Canada to Mexico and are either striped (Acalymma vittatum) or spotted (Diabrotica undecimpunctata howardi). Both species primarily feed on the leaves, flowers, and fruits of cucurbits (cucumbers, squash, pumpkins, and melons). Alternate plant hosts include beans, corn, peanuts, and potatoes.

Identification

Adult cucumber beetles (1/4 inch long) have dark heads, legs, and antennae. They can have 12 black spots or 3 parallel black stripes on their wings. During the growing season, they feed on seedlings, foliage, pollen, and flowers, causing reduced yields and sometimes plant loss. The slender white larvae (up to 1/3 inch long) have brown ends and injure plants by feeding on roots and underground stems. Heavy larvae populations can reduce plant vigor and damage melon rinds making the produce unfit for consumption or market.

Note: Adult and larval stages of the cucumber beetle transmit several plant diseases, including bacterial wilt and mosaic virus in cucurbits.

Western Striped Cucumber Beetle

The striped cucumber beetle (acalymma trivvittatum) is a major pest of cucurbits, feeding on the leaves and flowers of these plants. These beetles overwinter and emerge in the spring and feed on pollen. They then go on to lay their eggs in the soil which hatch around a week later. These are black-bodied with 3 parallel yellow stripes.

Striped Cucumber Beetle

Striped Cucumber Beetle

Western Spotted Cucumber Beetles or Southern Corn Rootworm

One of the most common and destructive pests of cucumbers is the spotted cucumber beetle (diabrotica undecimpunctata) These beetles are about 1/4 inch long and are yellow with 12 black spots.

Two Western Spotted Cucumber Beetles

Two Western Spotted Cucumber Beetles

Banded Cucumber Beetles

Mostly prone to warmer climates, Banded Cucumber Beetles (diabrotica balteata) are most prominent in parts of Florida, Arizona, and Texas. Adults are green with four broken yellow bands and have an orange head with copperish-colored antennas.

Banded Cucumber Beetle - Diabrotica Balteata

Banded Cucumber Beetle

 

Life Cycle

Adult beetles overwinter in plant debris and garden trash. Females leave their winter sites in early spring and deposit up to 800 orange-yellow eggs in the soil near the base of plants. In about ten days, hatching occurs, and the larvae feed for three or more weeks before pupating. First generation adults emerge ten days later. A complete life cycle requires 6-9 weeks. Up to four generations can be produced in a single growing season.

Cucumber beetles become active in late May or early June and grow to adults in mid-July to September.

How to Control

These beetles feed on the leaves of plants, leaving behind small holes. The feeding can also create lesions that can lead to infection and death of the plant. Infestations of cucumber beetle damage can be vast, so it is important to monitor your plants for signs of these pests and take steps to control them if necessary.

  1. Select resistant varieties whenever possible.
  2. Inspect plants frequently for beetles and handpick any that are discovered.
  3. Floating row covers are extremely effective when placed on seedlings and left in place until plants are old enough to tolerate beetle damage.
  4. Commercially available beneficial insects, such as ladybugsgreen lacewing and the spined soldier bug, will feed on pest eggs.
  5. Beneficial nematodes work well to curtail immature stages developing in the soil.
  6. When applied to plants, Surround WP (kaolin clay) leaves a fine powdery film that insects find unattractive for feeding and egg-laying.
  7. Spinosad, the active ingredient in Monterey Garden Insect Spray, is approved for organic use and works on a long list of insects found on vegetable crops.
  8. BotaniGard ES is a highly effective biological insecticide containing Beauveria bassiana, an entomopathogenic fungus that attacks a long list of troublesome crop pests – even resistant strains! Weekly applications can prevent insect population explosions and provide protection equal to or better than conventional chemical pesticides.
  9. If pest levels become intolerable, spot treat with a fast-acting organic insecticide. For best results, apply to the undersides of leaves and deep into the plant canopy where insects hide.
  10. Remove garden trash and other debris shortly after harvest to reduce overwintering sites.

Tip: Securely fasten row cover edges to ensure that beetles do not find a place of entry. Remember to remove row covers in early spring to allow for pollination.

Mosaic Virus Risks

Since these beetles enjoy feeding on watermelon, cucumbers, squash, and pumpkins, they often transmit the squash mosaic virus or cucumber mosaic virus, which significantly damages plants and reduces yields. This virus can quickly infect an entire garden, transmitting bacterial wilt and mosaic virus, so it is important to take steps to prevent its spread.

Biological control

Beneficial Insects

Introducing natural predators such as braconid wasps, some nematodes, ground beetles, tachinid flies, and soldier beetles early in spring can help keep your garden under control.

Ladybugs, assassin bugs, and green lacewing will also feed on cucumber beetles at different life stages.

One of the most common biological controls for cucumber beetles is the use of parasitic nematodes. Nematodes are small, worm-like creatures that parasitize insects and other small animals. When applied to soil, nematodes will seek out cucumber beetle larvae and parasitize them. This kills the larvae and reduces the population of cucumber beetles.

Neem Oil

Neem oil is an effective organic pesticide that can be used to control cucumber beetles early on. Neem oil works by disrupting the development of the beetle, preventing them from feeding and reproducing, causing them to die from starvation. Ensure you apply when bees and other pollinators are not active since Neem oil is slightly toxic to bees and other pollinators.

Trap crop

One way to help manage these pests is to use trap crops. Trap crops are plants that are planted near susceptible crops to attract Cucumber Beetles away from your primary crop. The idea behind using a trap crop is that the beetles will feed on the trap crop instead of the susceptible crop. This can help reduce the amount of damage done to the susceptible crop.

Mulch

One way to help protect your plants from cucumber beetles is to use aluminum plastic mulch. Mulching, using fabric, hay, straw, or plastic, will help keep the soil cool and moist, which will make it less attractive to the beetles. It will discourage the beetles from laying eggs.

Straw mulch may attract wolf spiders, which are natural predators of cucumber beetles.

 

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