How to Identify and Control Cucumber Beetle

The last thing you want to see in your yard is a cucumber beetle. If you are starting to see these little bugs scattered around your garden, you have a major problem. Cucumber beetle larvae feed on the roots of your plants, and the adult beetles chew on the foliage. Even worse, they spread plant disease.

So what can you do to eliminate the spread of cucumber beetles? I’ll tell you about the different types, how to get rid of them, and how to prevent them from becoming a permanent problem.

What are Cucumber Beetles?

The cucumber beetle falls into two separate insect genera, the Diabrotica and Acalymma. Both are part of the Chrysomelidae family of insects, which encompasses many of the beetle species.

While there are a number of different species in each genus, we’re going to focus on common food pests.

Types of Cucumber Beetle

Nearly all types of cucumber beetles (striped and spotted cucumber beetles included) can transmit plant diseases. The most commonly spread are bacterial wilt and the cucumber mosaic virus. So it’s essential to get rid of these before they eat or poison your plants!

Diabrotica virgifera

There are two subspecies of this insect, Diabrotica virgifera virgifera (the Western corn rootworm) and Diabrotica virgifera zeae (the Mexican corn rootworm). The two are so closely related that it’s incredibly hard to tell them apart, except by location.

In its larval form as the western corn rootworm, Diabrotica virgifera is one of the most destructive insects to corn crops in the U.S. It ranges from the southwestern edges of the “corn belt” all the way to the eastern coast. It also has spread to and throughout Europe, causing major issues in a number of countries there.

As adult beetles, Diabrotica vergifera are still quite damaging in that they continue to spread. It should be killed quickly once identified. Keep an eye out for this black and yellow beetle and strike back quickly!

Diabrotica undecimpunctata

This species also has multiple subspecies classifications. Those are:

• Diabrotica undecimpunctata howardi (the spotted cucumber beetle or southern corn rootworm)
• Diabrotica undecimpunctata undecimpunctata (the western spotted cucumber beetle)
• Diabrotica undecimpunctata tenella (the western cucumber beetle)

Spotted cucumber beetles are also major agricultural pests and should be destroyed quickly. These impact a wider variety of crops than the western corn rootworm does. These can be problematic for a number of cucurbits, beans, and more.

One thing that all three subspecies have in common is their coloration. This yellow beetle with black spots may have a different number or placement of their spots, but otherwise, they’re similar in their looks.

Cucurbit Beetle

Known in South America as vaquita de San Antonio. These striped cucumber beetles not only feast on cucurbits but on beans, grapes, and potatoes too.

They’re primarily located in and around South America and are a major agricultural pest in that region. While it’s prettier than some of the other cucumber beetle types, it can be quite destructive.

Banded Cucumber Beetle

The banded cucumber beetle is spread from the United States all the way south to Colombia and Venezuela. It has an extremely wide range of hosts. Some foods are cucurbits such as cucumber, melons, squash, and gourds. It also eats some cruciferous vegetables like cabbage, some nightshades such as tomato and potato, and more.

These striped cucumber beetles are not as prominent in the northern United States as the weather there is simply too cold for them to thrive. However, in the southern half, it’s become relatively widespread since its appearance in the late 1920’s.

Northern Corn Rootworm

Found primarily in the U.S. and Canada, the Northern corn rootworm is just as dangerous in cooler climates as the Southern corn rootworm is in warmer ones. This little insect has just as wide of a food preference as its southern relative and is equally dangerous in the garden.

Striped Cucumber Beetle

In the other genus which comprises the cucumber beetle population, we have the striped cucumber beetle. These beetles are a severe pest for crops in both larval and adult phases of life. It feeds primarily on cucurbits.

Adults prefer older plant foliage. The larvae feed on the root structure of the plants from within the soil. These beetles are primarily found in North America, specifically the central and eastern portions of the United States.

Western Striped Cucumber Beetle

This close relative of striped cucumber beetles is a variation that tends to stay west of the rest of its family. It has lots of similarities in terms of food crops. This might have been an evolution of striped cucumber beetles that prefer the hotter western climates.

Life Cycle

Adults mate when they are roughly a week in age. Roughly two weeks later, the female of the species will begin to lay eggs.

Depending on the species, they lay eggs in a variety of places. Generally, they prefer either the underside of leaves or flower petals for their laying area. Some species lay in large clusters every few days. Others opt to lay a few eggs every day.

When the eggs hatch, larvae emerge. These rootworms are tiny initially but grow to reach sizes of a quarter to a half inch in length. Growth happens in a series of larval cycles called instars. There are three to four of them for most species.

Once emerged, the larvae will tunnel into the soil at the base of their plant where they feed on the roots. This gives them some protection as they feed from any predators which might otherwise eat the larvae.

Once the larvae have grown over a period of a few weeks, they pupate in the soil. When pupation has concluded, the adult beetles will emerge and begin the life cycle anew.

Common Habitats

Adults are able to travel for short distances, and can slowly migrate throughout an area. Once spotted or striped cucumber beetles have found their ideal home, they tend to stay there for a while. Typically, this home is in an area where there is a plentiful supply of their preferred foodstuff.

Different beetles inhabit different areas depending on their species. Some species are incapable of overwintering (usually the warmer-climate species), but there are a few cold-weather varieties that do. These enter a state of diapause in compost piles or under soil. That’s almost like a state of suspended animation. Once warmer weather has returned, the adults emerge to continue life as normal.

What Do Cucumber Beetles Eat?

Other than the obvious cucumbers which they’re named after, cucumber beetles tend to be fond of cucurbits and corn as their primary crops. However, depending on the variety, the following plants may be impacted:

• Cantaloupe
• Squash
• Corn
• Soybean
• Potato
• Grape
• Tomato
• Wheat
• Watermelon

Cucumber Beetles As Disease Vectors

Cucumber beetles are known vectors for both mosaic virus and bacterial wilt. Both MV and bacterial wilt are incurable diseases that often result in the removal of infected plants.

Mosaic virus is a disease that affects many of the plants cucumber beetles feed on. Affected plants take on a mottled green and yellow appearance on their leaves, white banding along veins, or display yellow rings. While not always deadly, MV is highly communicable and easily spreads to other plants. Remove infected plants and destroy them to keep the disease at bay.

Bacterial wilt starts with the lightening of leaves and wilting of affected areas. Eventually, the leaves collapse and die away. Bacterial wilt may affect different plants in varying ways, but the best way to control the spread is to remove plants affected by bacterial wilt and destroy them.

Of course, the best way to control both MV and bacterial wilt is through the prevention of cucumber beetles.

How To Get Rid Of Cucumber Beetles

Obviously, it’s important to eliminate the striped cucumber beetle and spotted cucumber beetle as fast as you spot them, especially to remove the risk of bacterial wilt and MV. Read on as I tell you not only how to kill cucumber beetles, but how to make your garden less of a target!

Organic Control

As with any form of pest control, integrated measures that include companion planting to attract natural predators will be most effective. Cucumber beetles are notorious for being difficult to control with insecticidal options, making it difficult to prevent MV and bacterial wilt. Concentrate on environmental options first, moving to organic pesticides later.

When it comes to organic pesticides, there are a variety of options with varying levels of efficiency.

Start out with a blend of pyrethrin with potassium salts of fatty acids. This is a good overall solution and is also effective against leafhoppers, asparagus beetles, tomato hornworms, and more.

Oils tend to deter pests from taking up residence in your plants. They have the added bonus of smothering any eggs which are already in place. The oils also break down slower, which protects your plants longer. Some are also effective miticides if you’re having problems with spider mites.

Finally, if you want to give pyrethrins one more shot before moving onto something else, you can go for a strong solution of a pure pyrethrin spray option. Just blend it at the highest maximum recommendation on the label for your types of plants.

Some cucumber beetles are resistant to pyrethrins, so it’s good to have an alternative. In this case, I would recommend a spinosad spray. As they can negatively impact beneficial insect activity, use these methods as a last resort where possible.

Environmental Control

Your first stage in environmental control should always be to encourage beneficial insects that prey on your pests. These will not only help you control beetle damage, but they’ll also help prevent MV and bacterial wilt.

To do this, plant flowers or herbs that encourage ladybugs and lacewings to stick around your yard. These two insects will happily consume the eggs. They’ll also eat any newly hatched larvae they might encounter. Plants that attract these two include yarrow, cosmos, coreopsis, goldenrod, and Queen Anne’s lace.

Another beneficial insect for your arsenal is the spined soldier bug, which will quite happily suck the life out of cucumber beetles. They have a sharp spear-like proboscis that they will jab into garden pests to feed on bug juices. They’ll happily eat cabbage loopers, flea beetles, cabbage worms, and many more.

The most important predator of the cucumber beetle is the tachinid fly. These flies either lay eggs on the exoskeleton of adult cucumber beetles or inject their eggs within. Asters, chamomile, dill, parsley, and feverfew are just a small selection of the plants that attract tachinids.

Don’t neglect to add a protective force to your soil as well. Beneficial nematodes will attack larvae that might get under the surface of the soil, killing them quite effectively. A healthy population of beneficial nematodes in your garden beds will eliminate most pest larvae.

If the beneficial insects aren’t working, try planting trap crops. These should be plants that cucumber beetles are especially fond of. You will be effectively sacrificing these plants for the chance to kill the cucumber beetles, so don’t expect to get much of a harvest from them.

Prevention

Your best bet is to keep cucumber beetles from ever reaching your plants in the first place!

Treat your plants to a dusting of kaolin clay. This superfine clay leaves a film behind on the leaves of plants that insects don’t like to lay eggs on or eat. This prevents both spotted and striped cucumber beetles and the MV and bacterial wilt they spread.

Using floating row covers works extremely well to keep adult cucumber beetles from reaching your plants. If the spotted and striped cucumber beetles can’t get to the plants, they can’t lay eggs on them! You will either need to hand-pollinate your plants or remove the row covers when they flower. Otherwise, bees won’t be able to reach the plants either.

There has been some research into using vermicompost as fertilizer instead of using more traditional slow-release chemical fertilizers. So far, it’s showing that the striped cucumber beetle is less likely to strike plants grown in a vermicompost-rich plot. Researchers believe that this may be resulting from an increase in phenolic compounds in plants grown with vermicompost.

Since vermicompost is a great option as a fertilizer, it certainly can’t hurt to try it! Increasing your chances of growing healthy plants that have less contact with the beetles that spread MV and bacterial wilt is an added plus.

Frequently Asked Questions