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Cucumber beetles spread plant disease and lay waste to a wide variety of cucurbit crops in both home gardens and commercial farms.
In this article, we will examine the attributes of the cucumber beetle and share advice on keeping them under control in your farm or garden. Read on to learn more.
What Do Cucumber Beetles Look Like?
There are two types of cucumber beetles:
- Acalymma vittata (striped)
- Diabrotica undecimpunctata howardi (spotted)
The spotted cucumber beetle is also called the southern corn rootworm.
Striped cucumber beetles are about a fifth of an inch long. They are yellowish-green and have three lengthwise black stripes.
Another pest, the western corn rootworm beetle, is similar in appearance but does not damage vine crops. You may find this insect feeding on cucurbit blossom pollen.
To tell the difference between the striped cucumber beetle and the western corn rootworm beetle, look at the abdomen.
Western corn rootworms have yellowish-green underbellies. Striped cucumber beetles have black underbellies.
The spotted cucumber beetle is also yellowish-green but has a dozen black spots instead of stripes.
The Life Cycle Of The Cucumber Beetle
Adult female cucumber beetles lay eggs at the base of the plant upon which they prey.
When larvae hatch and emerge, they feed on the roots of the host plant for two or three weeks before they begin their pupation phase.
This also takes place in the ground soil surrounding the base of the host plant.
The climate determines how many generations the beetles may produce annually. In some areas the weather is too cold for the adults to overwinter at all.
In these areas, adults may migrate south for the winter and return in the spring.
In other areas, adult beetles may live for a couple of years and produce half a dozen generations per growing season.
What Does The Cucumber Beetle Eat?
When spring comes, the adults awaken or return and begin feeding on the pollen and leaves of a wide variety of shrubs, trees and weeds.
However, cucumber beetles prefer cucurbits because of the chemical (cucurbitacin) which they produce.
Other types of vegetation sustain the beetles until their favorite meals become available.
Adult beetles especially enjoy feasting on the leaves, blossoms and fruit of cucurbits such as:
- Summer squash
- Winter squash
Damage: It is entirely possible for the adult beetles to kill young plants as they feed.
Although larvae feed on the roots of mature cucurbit plants, this does not do much damage to the plants.
If the plants have low-hanging ripe fruit that rests on the soil the larvae may also chew holes in it.
Although these pests do cause a great deal of direct physical damage, that’s not the worst of the problems they cause.
In addition to chewing up leaves, flowers, roots and fruit, cucumber beetles transmit Erwinia tracheiphila, a pathogenic bacterium that is the cause of bacterial wilt in cucurbit crops.
Adult beetles pick up the bacteria by eating infected weeds early in the season and then transmitting the bacteria to squash and melon plants when they become available.
When beetles feed on an infected plant they pick up the bacteria with their mouthparts.
When they move on to feed on another plant, it also becomes infected. The bacteria may also be transmitted through feces.
Erwinia tracheiphila multiplies in the plants’ xylem.
This causes the xylem tissue to become clogged so that water and nutrients cannot be delivered throughout the plant.
This causes the plant to wilt and eventually to die.
How To Be Sure The Problem Is Bacterial Wilt?
You may suspect that bacterial wilt has begun when individual lateral leaves begin to wilt. Soon after, the entire plant succumbs to wilt and perishes.
When you observe a wilted stem, clip it in half. Hold the cut end of the stem against the part that is still on the plant.
Keep it in position for ten seconds and then pull it apart slowly.
If you see something that looks like white string or spider’s silk stretching out between the two parts of the stem, you will know that the problem is bacterial wilt.
This viscous material is a mixture of the sap of the plant and the Erwinia tracheiphila bacterium.
This infection is a serious problem. Even if only about ten percent of the beetles affecting your crop are infected with this bacterium, the damage it causes can be severe. [source]
Squash Mosaic Virus
Bacterial wilt does not typically affect pumpkins and squash, but it can affect other types of melons.
The cucurbits most severely affected by this malady are cantaloupe and cucumbers.
Squash are badly affected by squash mosaic virus, which cucumber beetles also transmit. This causes an ailment called “squash mosaic” which affects all sorts of squash and melons.
This disease manifests as reduced growth and reduced yield. It causes fruit to become distorted, mottled and unmarketable. [source]
How To Control Cucumber Beetles
Once a plant is infected with bacterial wilt there is no hope for it.
That’s why it is very important to begin cucumber beetle control very early in the growing season.
The sooner you can stop them, the more control you will have over the spread of this pathogen and squash mosaic virus.
Keep a sharp eye out for these pests. Examine your plants several times a week starting very early in the season.
Especially look around the edges of the fields as this is where they will first show up.
Start treatment the minute you see cucumber beetles.
If the population of beetles is allowed to increase, the likelihood of bacterial wilt transmission will also increase.
5 Tips For Organic Cucumber Beetle Control
- Treat for cucumber beetles by picking the adults off leaves and stems and dropping them into a bucket of soapy water. If you see any infected plants, remove them and destroy them immediately.
- Organic neem oilused as both a foliar spray and a soil drench is an effective weapon against many kinds of garden pests.
- Introduce Entomopathogenic nematodes to your garden soil to keep many different sorts of ground-dwelling larvae under control.
- Sprinkling diatomaceous earth is great to deal with many different kinds of garden pests.
- Use kaolin clay to coat plants and deter cucumber beetles and other pests.
White Kaolin Clay – 2 lb
Use Kaolin Clay to make a foliar spray that acts as a barrier between plants and a variety of pests. The clay does not kill them, it just prevents the pest from eating leaves.
It is effective against:
…to name a few.
How To Use Kaolin Clay
To use this natural foliar spray you just mix about three cups of the clay with a gallon of water.
It’s best to do this by putting the clay in a dry bucket and then gradually stirring in the water. This helps prevent clumps and sticking.
It’s a good idea to cover your mouth and nose with a paint mask or bandanna while you do this to avoid breathing in the dust.
Once you have your mixture, put it in a hand pump backpack sprayer or a regular spray bottle. Apply the mixture over all surfaces of your plants on an overcast day.
It is also possible to use this mixture as a “dip” for seedlings in trays:
When the mixture dries it leaves a fine powder coating that baffles insects seeking a tasty cucurbit meal.
It’s important to understand that this is not a one-time fix. You’ll need to spray about once a week and after every rain. [source]
Cultural Pest Control
Many small gardeners have found that floating row covers do a good job of preventing cucumber beetles from accessing plants.
After the plants flower, take the row covers off so that bees can pollinate. Alternately, you could hand-pollinate your plants if you only have a small patch of cucurbits.
Other non-chemical methods of controlling these pests include trap cropping and mass trapping.
These techniques are an important part of an Integrated Pest Management (IPM) plan that strives to control pests using few or no toxic substances.
What Is Trap Cropping?
Trap cropping is a decoy method that works by planting plants attractive to cucumber beetles around the edges of the field or garden.
These plants lure the pests in and stop them from attacking the main crop.
When the insects gather on the trap crop plants they become “sitting ducks”.
The beetles are much easier to pick off or treat with neem oil or other insecticides when the beetles all gather in one place.
What Plants Make The Best Trap Crop?
Lincoln University’s IPM program has been conducting research on this topic for over 15 years. According to these experts, the “vegetable” Blue Hubbard squash is an all-time favorite of cucumber beetles. This makes it a superb choice to grow as a trap crop.
Trap cropping is beneficial in many ways.
Not only is it an effective way of getting rid of cucumber beetles (and incidentally squash bugs) it also helps farmers and gardeners save money and time through reduced use of insecticides and reduced labor battling bugs.
Additionally, trap cropping is not harmful to beneficial insects and pollinators.
Some farmers and gardeners using this method are able to leave their food or cash crops entirely pesticide-free and only treat the Blue Hubbard seedlings with insecticide prior to planting them out.
This reduces the chance of accidentally and negatively impacting helpful insects. Additionally, this method produces cleaner, healthier cash or food crops.
Plant Trap Crops Before Cash Or Food Crops
Timing is important in using trap crops. Start Blue Hubbard seedlings indoors late in winter or early in the spring.
The Blue Hubbard seedlings should be at least two weeks old when you plant your cucurbit crop.
Transplant the Blue Hubbard seedlings to the edges of your garden or field when you plant your cucumber, melon and squash seeds.
If you plan to start your cucurbit crop using transplants, you must plant your Blue Hubbard squash a couple of weeks before you transplant your cucurbit crop.
How Many Trap Crop Plants Must You Plant?
You needn’t plant a big crop of Blue Hubbard squash. Research has indicated that just six or eight trap crop plants will effectively draw cucumber beetles away from as many as a hundred cucurbit plants of other varieties.
If you have a small garden or farm with cucurbits planted in rows with plastic mulch with drip irrigation, it is best to plant between two and four Blue Hubbard seedlings at each end of every row. [source]
Traps Controls: What Is Mass Trapping?
Another method studied by the LU IPM program is mass trapping. This is a simple, but effective technique that really adds power to your cucumber beetle battling arsenal.
These simple traps are very attractive to both types of cucumber beetles and actually draw them away from your crops.
When the beetles enter the traps they eat bait that has been laced with insecticide and then they die.
These simple traps are made up of three parts:
- A large milk or juice jug painted yellow with small openings drilled or cut into the sides
- A floral based attractant or lure (AgBio© floral lure)
- A “stun pill” made of powdered buffalo gourd, paraffin wax and insecticide designed to kill insects
A test conducted in 2011 resulted in the death of 2531 cucumber beetles with the use of only 28 baited traps over a nine-day period of time.
Another test conducted in 2015 resulted in the demise of 3715 beetles in an eight week period of time.
In both cases, the beetle control was effective enough to significantly reduce the need for insecticide.
Furthermore, this effective control insured that the crops being protected produced high quality, low-or-no insecticide, marketable fruit.
For information regarding where to purchase the attractant and the stun pill, see Integrated Pest Management: University of Missouri [source]
What About Sticky Traps?
There are a number of videos and articles providing instructions for making sticky traps for cucumber beetles.
By-and-large, sticky traps are never a good idea. These traps pose a hazard to beneficial insects and other wildlife.
When using sticky traps, you run a risk of accidentally trapping beneficial insects which help keep cucumber beetles under control.
Among these are Soldier beetles, Tachinid flies and Braconid wasps (excellent for tomato hornworms too). Pollinators such as bees and butterflies are also put at risk by sticky traps.
It’s easy to see that keeping cucumber beetles under control is a very important aspect of preventing physical crop damage and the spread of bacterial wilt and squash mosaic.
This can be quite difficult because cucurbits are very sensitive to chemical insecticides.
Use of pesticides can cause more damage than the beetles and the diseases they bring. It is especially important to avoid Malathion as it will burn leaves.
Carbaryl (aka: Sevin) is effective against cucumber beetles, but be sure to apply it at dusk to avoid contact with bees and other beneficial pollinators. [source]
One product that is specifically formulated to affect cucumber beetles without dramatically affecting bees is called Adios®.
This product is a combination of cucurbitacin and a very small dose of carbaryl.
The purpose of the cucurbitacin is to spur the beetles to eat compulsively. This causes them to consume mass quantities of the poison.
This combination specifically targets the pests and avoids harming beneficial insects. [source]
Controlling Cucumber Beetles With Integrated Pest Management
Cucumber beetles can be a real challenge for the home gardener and the commercial farmer.
Because the threats they present are multiple, it is very important to employ a well-designed IPM program that attacks them on multiple fronts at every phase of their lives.
By watching for them early and picking them off one-by-one, employing the help of beneficial insects, using cultural and organic control methods and turning to safer pesticides as a last resort, you can reduce and control your cucumber beetle population.