6 Common Pests That Eat Potatoes Underground

Let me just say it: potatoes are delicious. But it isn’t just us who are fond of potatoes, some pests can do a number on them, and they aren’t afraid to dive right in. So how do you keep those pesky insects at bay?

6 common pests that can eat your potatoes underground include potato flea beetles, wireworms, and potato tuber moths. You may also often find white grubs,  cutworms, and Colorado beetles destroying your crops from beneath the soil.

In this article, I’ll discuss the different types of pests that can attack potatoes and what you can do to eliminate them. Keep reading to find out more.

1. Potato Flea Beetles

The potato flea beetle mainly attacks potatoes but also affects eggplants, tomatoes, and cucumbers, among other plants. 

Potato flea beetles measure less than two millimeters in length and are black with brown antennae and legs. They appear on all parts of the potato plant above ground and the soil surface. Generally, these insects feed on upper and lower leaf surfaces.

Once you notice flea beetles on the leaves, their larvae are likely munching away on your underground tubers. The larva is typically a thin white grub with a dark brown head and tiny legs. Usually, the larvae live in the soil around potato roots, but they’ll enter the tubers, resulting in small pimples or hollows on the tuber, often filled with corky matter.

Potato Flea Beetle Life Stages

  • Egg. The female lays tiny eggs in shallow cracks on the ground around plants. In terms of appearance, the eggs are white and oval.
  • Larva. Within seven to ten days, larvae emerge as a whitish elongated soft-bodied grub with a yellow or brown head. The larvae mainly feed on potato roots, underground stems, and tubers. They grow to maturity in about 4 to 5 weeks, then become pupae in the soil.
  • Pupa. Pupation is short, it takes approximately a week for the pupae to develop, and the adult emerges to attack the potato leaves.
  • Adult. In adults, their bodies are oval, and their colors range from brown to black.

Potato Flea Beetle Damage to Crops

Adult flea beetles feeding on foliage results in small sieve-like holes of up to 5 mm (0.2 in) in diameter with mild chlorosis on the leaves.

When it comes to the tubers, the flea beetle will enter them and drill inside, leaving small raised bumps on the tuber surface or hollows.

Potato plant damage, either by adult insects on leaves or larvae on tubers and roots, along with the spread of pathogens, leads to lower production.

Potato Flea Beetle Management

Eliminating flea beetles isn’t usually possible; you need to control them for as long as possible for the seedlings to outgrow the risk.

Management in an Organic Garden

There are many ways you can use for controlling flea beetles organically. So if you don’t want to resort to chemical pesticides, below are the most effective organic control methods you can try in your garden:

  • Use Neem oil. Neem oil is a natural insecticide effective against insects and works well against flea beetles organically. Spray directly on the leaves.
  • Make an organic homemade spray. You can mix one tablespoon of mild organic liquid soap with 1 liter of water to make your own organic flea beetle spray. Spray it directly on the insects.
  • Diatomaceous earth (DE). The product contains ground-up fossilized organisms. You can sprinkle it directly on the flea beetles or around the roots of the infested plants.

Pest management in a Non-Organic Garden

You can use insecticides targeting other insects on potato plants to control flea beetles. About two weeks after the first adults emerge, use the recommended insecticides that typically contain spinosad. You can apply several commonly available, effective systemic insecticides for controlling adults to the soil.

How To Keep Flea Beetles Away From Your Garden

If you are experiencing a potato flea beetle menace in your garden, here are some prevention tips:

  • Flea beetles are more likely to exist near uncultivated land next to fields where potatoes are grown because the vegetation in these areas is a food source for the beetles.
  • The adult flea beetles overwinter in fallen leaves and other garden debris, so make sure you clean your vegetable garden every fall.
  • Flea beetles hibernate in the soil, expose the adults and kill them by tilling or turning your garden soil in the fall.
  • Flea beetles cause the most damage to young seedlings in the early part of spring, so if you wait a few weeks before planting, they’ll be able to withstand the attacks better.

2. Wireworms

Wireworms are slender, yellowish larvae of the click beetle. The larvae of the click beetle cause damage to crops, not the adults.

Wireworm Life Stages

  • Egg. Click beetles lay between 50 to 300 eggs in grassy fields. The hatching period is about three- to four weeks, then the larva or wireworm appears.
  • Larva. As the larvae grow, they eat plant waste, weeds, or roots. Temperature, moisture, and food determine larvae’s movement upward or downward in the soil.
  • Pupa. The pupae will develop in the ground and into click beetles within a few days.
  • Adult.Wireworms hatch out of eggs after about two weeks. They’re white and measure about 1½ mm (0.06 in) long when they first emerge from their shells. After some time, they turn yellowish or light brown, with an even shinier surface. A larva’s life cycle can last anywhere from three to six years, with two to five years spent actively eating.

Wireworm Damage to Crops

When spring comes around, wireworms start tunneling into the potato’s roots and shoots, weakening the potato plant. Later as the planting season continues, wireworms dig into potatoes’ tubers, destroying them. The result is round holes 3 mm (0.12 in) in diameter and 4 cm (1.56 in) deep lined with tissue, affecting growth.

Wireworm Management

Wireworms are problematic insect pests due to their long life cycles. The adult female wireworm can lay up to 300 eggs at a time, and the resulting larvae can live for up to five years underground, feeding on the roots of plants.

Pest Management in an Organic Garden

  • You should plan for proper crop rotation if the wireworm population is high, but avoid planting grains such as barley and wheat in potato rotations to minimize the risk of wireworms.
  • By growing various crops in your garden each year, you can break the life cycle of this pest.
  • The larvae can also hibernate in the soil, expose and get rid of them by tilling your garden soil.
  • You can irrigate your garden, forcing the larvae underground to turn up.
  • You can also try sprinkling diatomaceous earth on the soil to kill the worms; my recommended brand is St. Gabriel Laboratories Insect Repellent (available on Amazon.com).

Pest Management in a Non-Organic Garden

The most effective insecticides contain bifenthrin, pyrethrins, and zeta-cypermethrin as the active ingredient. You can purchase them in granules or liquids to use in your home garden.

When soil samples indicate a high presence of wireworms, but you can’t avoid or delay planting, the option for control is to apply an insecticide. For the best results, apply insecticides in the soil to a depth of 12 to 15 cm (4.7 to 5.9 in) before planting.

3. Potato Tuber Moths

The potato tuber moth (PTM) consists of several species. Phthorimaea operculella, the most common, is widespread worldwide and even in the United States. The potato moth is a destructive insect and causes extensive damage to potatoes.

Potato Tuber Moth Life Stages

  • Egg. The female lays between 150 and 200 eggs on the back of leaves or near targeted tubers’ eyes. The eggs are oval-shaped and less than 1 mm (0.04 in) in diameter.
  • Larva. Freshly hatched larvae are gray, cream, or yellowish-white with a brown head. The larval period lasts between 15 and 20 days.
  • Pupa. Development takes place among dead leaves or debris, in soil, or on stored tubers. This period lasts about 12 days. Yellowish-colored pupae appear at the end of the pupal stage.
  • Adult. The adult is a tiny grayish-brown insect. A complete life cycle lasts 20 to 30 days at optimum temperature and humidity conditions.

Potato Tuber Moth Damage to Crops

Potato tuber moths attack several crops but mostly potato crops. Foliage damage occurs when the tuber worm digs into leaves, eats the inside, leaving only a dried-up outer skin, then infects the stem tissue, causing the plant to die.

When falling larvae dig through cracks in the soil and enter the tubers, the larvae activity will ruin the tubers. Another way is when the female lays its eggs on top of exposed tubers near the eyes. When they hatch, they will tunnel into the tuber through the eye.

Potato Tuber Moth Management

The potato tuber moth (PTM) is a serious problem for potato growers. The damage they cause can reduce yield and quality and make the potatoes unmarketable. However, there are some measures you can take to control the problem.

Pest Management in an Organic Garden

In an organic farm, you may opt for the following control measures:

  • Protect the moth’s natural enemies. They play an essential role in the biological control of potato tuber moths. For example, ladybird beetles, spiders, and dragonflies feed on their eggs and larvae.
  • Infested tubers. Infested seeding tubers are the leading cause of re-infestation in the field, so use healthy, clean seeds.
  • Harvesting. As soon as the crop matures, begin harvesting since the pest will infect tubers left on the farm for extended periods.
  • Provide adequate water. It’s essential to irrigate the ground to avoid soil cracking.
  • Get rid of volunteer potato plants. Before planting new potato crops, remove any volunteer potato plants.
  • Compact hilling. Compacting soil around emerging potato growth aims to keep moths from reaching the tubers to lay eggs. 
  • Remove all plant residues. Otherwise, the pest will pupate in the tubers and dry stems left in the field.

Pest Management in a Non-Organic Garden

Acetamiprid and imidacloprid, the insecticides used on leafhoppers and aphids, are effective against potato tube moths in the early season, shortly after planting. These broad-spectrum pesticides suit various plants, including leafy vegetables and fruit trees.

4. White Grubs (Sand Chafer)

Generally, white grubs pertain to several beetle species harmful primarily to grass crops. The white grub that affects potatoes is the sand chafer (Strigoderma arboricola). The adult beetle sand chafer’s larva is the white grub.

White Grub Life Stages

  • Egg. Once they appear from the ground, adults mate, and the females deposit their eggs in the soil. Females lay 50–100 eggs individually or in groups in small cells—the eggs hatch after 11 to 25 days.
  • Larva. These larvae are relatively large, up to 3 cm (1.18 in) long, and with three sets of legs. They have hard, ruddy-brown heads. It takes up to seven months for white grubs to develop, which is the time they feed on underground tubers.
  • Pupa. During the winter, the larvae stay deep in the ground for five to ten months before emerging in spring as the soil warms up, pupating and becoming adults.
  • Adult. All other life cycle stages are below ground except the adult stage. Sand chafers have rusty-red wings and black bodies.

White Grub Damage to Crops

In this pest life cycle, larvae are the most destructive as they feed little before the pupa stage. In their development process, the grubs feed on roots, then move on to tubers, where they make shallow circular holes.

White Grub Management

Pest Management in an Organic Garden

White grub infestation is more prevalent in soils with a large amount of organic matter and in soils treated with manure.

  • Utilize bird predators to control white grub populations.
  • Avoid planting potatoes in fields previously covered with grass.
  • To reduce the white grub menace and grow potatoes successfully, you should plant them away from grassy edges.

Pest Management in a Non-Organic Garden

There are limited options for chemical control of white grubs; so far, the most effective treatment is using carbofuran, a systemic insecticide (Furadan). Plus, you can also try the following pesticides:

  • Aldicarb granules, a systemic insecticide
  • Chlorpyriphos,a contact insecticide
  • Ethoprophos granules, a contact insecticide

You should conduct the chemical treatment when the larvae are young since older ones are more robust and will go deeper.

5. Potato Cutworms

Potato cutworm is about 22 to 26 mm (0.87 to 1 in) long and grayish brown. Fully grown ones can reach up to 48 mm (1.89 in) long. Their development from eggs to adults takes up to 36 days.

Potato Cutworm Life Stages

  • Egg. Females emerge at dusk and lay about 200 to 350 eggs in the soil or on the leaves of host plants. The eggs are white and cylindrical.
  • Larva. The larvae are yellow or blackish-green in color, about 1.5 mm (0.06 in) long, with black heads. The full-grown larva is approximately 42-45 mm (1.65-1.77 in) long, dark brown, and lives underground. It takes between 30 and 34 days for the larva to develop.
  • Pupa. Pupae are brown to dark brown, and pupation takes 10 to 30 days underground.
  • Adult. The adult is dark, with gray spots on the back and dark markings on its wings. The lifespan of an adult is seven to ten days.

Damage to Crops

These insects destroy plants and tubers, particularly at night. The presence of large boreholes in tubers is an indication of damage. These pests attack young plants by tearing their stems, dragging the plant into the ground, and consuming them, especially between 25 and 35 days after planting.

Potato Cutworm Management

Pest Management in an Organic Garden

  • Plowing exposes the pests to natural predators and the sun, dehydrating them.
  • You should prepare the fields and eliminate weeds and vegetation at least two weeks before planting so you don’t expose the new crop to cutworms.
  • Plow grassland in late summer or early fall before rotating to potato to reduce the number of eggs laid.
  • Before planting, irrigating the field is an effective way to kill cutworm caterpillars present in the soil.
  • Rather than manure, incorporate compost into your garden soil because green manure generally encourages egg-laying by the pest.

Pest Management in a Non-Organic Garden

There’s a strong recommendation against using chemical treatments for cutworms.

  • Pesticides are unnecessary in the home garden unless there’s a severe problem. You can apply pesticides to the stems or leaves if the problem is unmanageable. The most common pesticides used to control cutworms are carbaryl, cyfluthrin, and permethrin.
  • Insecticides applied to the soil to control other pests can also be effective against potato cutworms.

6. Colorado Potato Beetles

Of all the potato pests, the most widespread is the Colorado potato beetle (Leptinotarsa decemlineata). Initially discovered in Nebraska, experts later identified this pest in Colorado. The orange and black stripes on the bodies make them quite noticeable.

Colorado Potato Beetles Life Stages

  • Egg. The females lay eggs on the leaves of the potato plants. These eggs are oval and yellow to bright orange, laid in groups of 10 to 30 eggs. The laying of eggs can take up to a month; after four to ten days, the eggs hatch.
  • Larva. Larvae are orange-reddish slugs with two rows of black dots on each side of the soft shell. During this stage, larvae are at their most destructive, eating foliage as they grow. After about five weeks, the larva will drop onto the ground to pupate.
  • Pupa. The pupae are small and live in the soil. After the pupa has developed for five to ten days, the adults appear.
  • Adult. The adults have a convex shape with a hard shell and yellow wings with black stripes running across the back.

Colorado Potato Beetles Damage to Crops

The larvae are the most destructive; they’ll eat the leaves leaving just a skeleton of veins.

Damage to vines affects yield by denying foliage for tuber growth and will also affect tuber quality. A severely damaged plant may also become stunted.

Colorado Potato Beetle Management

Pest Management in an Organic Garden

  • Spray the plant with neem oil. Neem oil is the organic gardeners’ favorite insecticide. It reduces insect feeding and interferes with their hormone system, preventing reproduction.
  • Pick them off by hand. Ensure that you check your potato regularly for eggs and larvae. You’ll likely find larvae if you spot an adult beetle among your plants. Pick the beetles, larvae, and eggs and immerse them in soapy water to kill them.
  • Encourage natural predators. Ladybugs and stink bugs eat Colorado potato beetle larvae. You can intentionally introduce them in your garden. A bird-friendly garden is also beneficial because birds eat adult and larval insects.

Pest Management in a Non-Organic Garden

To control Colorado potato beetle in garden potatoes and other crops like peppers and tomatoes, apply carbaryl to the plants after the larvae emerge. Take care not to eliminate honey bees by treating around the flowers.

How To Keep Colorado Potato Beetles Away From Your Garden

The best way to deal with an infestation is to stop it from happening. Therefore protect your potato crop from beetles by trying the following tips:

  • Crop rotation. Avoid growing potatoes in the same spot every year.
  • Consider companion planting. Several plants repel potato beetles. You can interplant a few of them with potatoes.
  • Incorporate straw mulch into your garden. Straw mulch provides an ideal habitat for predators of Colorado potato beetles.

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