The Colorado potato beetle (Leptinotarsa decemlineata) is by far the most damaging pest for both backyard and commercial potato growers. These tiny beetles with orange and black stripes are prodigious breeders, and each female can lay up to 25 eggs at a time. Once the eggs hatch, the larvae, small orange insects with black heads and rows of black spots along the sides, do the majority of the damage to potato and other nightshade plants, peppers, eggplant, and tomatoes. They have voracious appetites and gradually defoliate a plant almost entirely.
As many gardeners soon realize, these beetles are extremely difficult to get rid of. They have adapted resistance to most control methods, both conventional and organic. As a result, your best weapons for dealing with the Colorado potato beetle are vigilance and speed.
5 Ways to Get Rid of Colorado Potato Beetles Organically
There are several methods that work well against potato beetle if plants are already infested. They all require that you pay close attention to what is happening in the garden and act quickly. If you can start combating the beetles as soon as you see evidence of them you have a better chance of saving your potato crop. It's best to spot the pest at the larval stage, as it's estimated that up to 75 percent of the damage occurs before the larvae mature into adult beetles.
Use Neem Oil
Apply neem oil as needed. This is the organic gardener's go-to insecticide, and it works wonders—even better than most conventional options. Neem oil is extracted from the seeds of the neem tree, and it contains several compounds that are found in commercial pesticides. It works by reducing insect feeding and interfering with the hormone system, hindering their ability to reproduce.
While neem oil is considered and organic pesticide, remember that just because a product is considered organic does not mean it is harmless to humans. The term "organic" means that the product is made from naturally occurring ingredients, not that it is non-toxic.
Neem oil, for example, is relatively safe in the way it is used as a spray pesticide since it requires insects to literally eat the plant in order to be affected by it. But it can cause allergic reactions to the skin, and you should be careful when spraying it, as ingesting it has been known to cause digestive problems.
Some other organic pesticides, though entirely safe to humans and pets, may be toxic to aquatic life, so take care not to allow excessive runoff.
Hand-pick beetles, larvae, and eggs and throw them in a bucket of soapy water to kill them. Regularly check the undersides of your potato leaves for eggs and larvae. If you spot an adult beetle among your plants, you will be sure to find larvae as well.
Adult beetles return to burrow under the soil at night around the base of your nightshade plants. Look for them there early in the day and toward the top of the plant later on as the beetles move toward the newest freshest and most tender leaves.
Use a Vacuum Cleaner
Use a vacuum to remove beetles, larvae, and eggs. There are special "bug vacs" for garden use, but a regular household handheld vacuum also works well.
Use Deterrent Sprays
Keep in mind that beetles, which generally have a hard carapace, are best treated with contact deterrent sprays when they are still in the soft-bodied larval stage. Several of these products are officially categorized as organic products, such as those containing spinosad or azadiractin. Spinosad is a pesticide derived from fermenting natural soil organisms, but it works only on the larval stage of the beetles and will not affect adult Colorado potato beetles. Spinosad is the better deterrent; it will need to be reapplied every 10 to 14 days during the larval stage of the beetles.
Bt (Bacillius thuringiensis var. tenebrionis) can be effective if it is introduced into the soil very early, while the insect is just beginning the larval stage. Thus, you will need to identify the eggs and apply Bt at this time in order for it to be effective. Bt is a soil bacteria that effectively paralyzes the digestive systems of certain insects at the larval stage, thereby starving them to death. There are many strains of Bt that have been developed; make sure to use the particular strain known to be effective against Colorado potato beetles.
Encourage Natural Predators
Stink bugs and ladybugs eat Colorado potato beetles, especially at the larval stage. They can be introduced artificially if your garden does not already have them. Predator insects alone aren't enough to control the population but they can be one tool in the arsenal.
A bird-friendly garden that encourages chickadees, wrens, sparrows, finches, nuthatches, mockingbirds, cardinals, and swallows will also help, as these birds can consume their own weight in insects daily. These bird species are all known to eat Colorado potato bugs.
What Causes Colorado Potato Beetles?
Colorado potato beetles are native to the Rocky Mountain region but are now found in every state except Alaska, Hawaii, and Nevada. They will be most prevalent where large groups of nightshade plants are close together; spacing your potatoes, peppers, or eggplants wide apart may help reduce populations.
Colorado Potato Beetle vs. False Potato Beetle
An insect that is often confused with the Colorado potato beetle is Leptinotarsa juncta, commonly known as the false potato beetle. Gardeners in the mid-Atlantic and Southeast U.S. may well see this insect rather than the true potato beetle. It takes close examination to tell the difference, but the false potato beetle will show a light brown strip interrupting the alternating white and black stripes on the back. The true potato beetle does not have this brown strip. Further, you will not experience the same serious plant damage, as L. juncta is not a serious problem with potatoes.
How to Prevent Colorado Potato Beetles
Preventing an infestation in the first place is easier than treating one that has already occurred. Protect your potato crop from beetles by trying several of these methods together, especially if you've had a problem with potato beetles in the past.
- Practice crop rotation: Don't grow potatoes in the same spot year after year. The adult potato beetles overwinter in the soil of the previous year's potato patch. If you plant in the same spot as last year, you're giving the beetles convenient access to your plants. They'll pick a plant, find a mate, lay eggs, and the cycle will continue.
- Practice companion planting: There are several plants that deter potato beetles. Try planting at least one or two of them alongside or even interplanted with your potatoes. A few good options include catnip, tansy, and sage. Be aware that catnip and tansy can spread easily. You can keep them in check by not letting them go to seed and by pulling any unwanted young plants right away. Several varieties of sage are pretty good about staying in place.
- Use straw mulch: Mulching heavily with straw not only helps keep the tubers out of the sunlight but also creates a habitat for predators of the Colorado potato beetle. If you can attract ground beetles, ladybugs, and green lacewings, they'll do a lot of the hard work for you.
- Plant resistant or early varieties: Certain varieties of potatoes, such as Russet Burbank, have proven to be resistant to potato beetles. Another good practice is to plant early varieties since potato beetle damage only gets worse as the season goes on and all the eggs hatch. Consider planting Caribe, Norland, or Yukon Gold potatoes; these are all great early-season options.
Where Does the Colorado Potato Beetle Come From?
This insect is native to the entire Rocky Mountain region, not just Colorado. But it is now found in every U.S. state except Alaska, Hawaii, and Nevada, and is widely spread through Europe and Asia, reaching across the ocean during the late 1800s, probably through shipped agricultural products.
What Do the Eggs Look Like?
The eggs of the Colorado potato beetle are very tiny, yellow to orange in color, and are laid in clusters along the undersides of the potato plant's leaves. If you can identify the eggs, you stand a good chance at controlling the Colorado potato beetle before it gets a foothold in your potato patch.
What Does the Plant Damage Look Like?
As the larvae and adult beetles feast on potatoes or other related plants, they will become gradually defoliated. The plants can usually survive up to 30 percent defoliation, but beyond this, the damage may kill the plant.
Do Colorado Potato Beetles Damage Other Plants?
If you experience damage to potato plants from this beetle, chances are good you will find similar problems with other vegetables in the nightshade (Solanaceae) family of plants. This includes eggplant, tomatoes, peppers, and ground cherries.
Will Colorado Potato Beetles Go Away on Their Own?
This insect is a prolific egg layer with a very fast maturation cycle. It quickly evolves resistance to pesticides and it overwinters deep in the soil. These genetic advantages mean that once you find it in your garden, it's likely you will deal with Colorado potato beetles for years to come. Unlike many beetles, this is not one that goes through periodic cycles where it may largely disappear for years at a time.