Common in home gardens across North America, wireworms (up to 1-1/2 inch long) are tough slender worms with shiny skin and three pairs of legs just behind their head. They are yellow to brownish-red in color and feed entirely underground, attacking germinating seeds, roots, bulbs and tubers. Damaged plants soon wilt and die. If infestations are heavy, thin and patchy crops may appear in the garden and reseeding will most likely be necessary.

Note: Wireworms are the larval stage of click beetles. Approximately 1/2 inch long, these brown to black colored, bullet-shaped beetles are notable for their ability to click and right themselves when placed on their backs.

Contents

Life Cycle

Wireworm larvae and adults overwinter in the soil. In early spring female beetles emerge from the soil, mate and lay eggs underground. Hatching takes place in 2-4 weeks, and the young larvae begin working their way through the soil in search of food. Larvae feed underground for 2-6 years with most of their damage occurring in early spring when soil temperatures are cool. Pupation occurs in late summer and adult beetles emerge in the spring. One generation per year, the life-cycle requiring 1-6 years to complete.

How to Control

  1. Thorough cultivation of the top 6- to 8-inches of soil makes conditions unfavorable to the egg laying adults and exposes all stages of the pest to weather and natural enemies.
  2. Birds can consume large amounts of larvae. Encourage them by hanging houses and feeders near your garden.
  3. Crop rotation is especially important to the organic vegetable grower because it can help reduce many pest problems that lead to the use of pesticides.
  4. Potatoes make great wireworm traps. Cut a potato in half and run a stick through the middle. Bury the spud about one inch deep so that the stick stands vertically as a handle. Pull the traps out after a day or two and discard wireworms.
  5. Apply Beneficial Nematodes when planting to attack and destroy developing pests in the soil. One pint — 10 million active units — treats up to 550 square feet of planting area.
  6. EcoSMART Organic Insect Killer can be used around home foundations, lawns and landscapes (ornamental and flower gardens). Apply 2-5 lbs over 1000 sq ft every 2-4 weeks or as needed.
  7. Apply SNS 203, made from 100% pure food grade materials, as a soil drench to kill the eggs and larval stages. Mix 2-4 oz per gallon of water and thoroughly wet affected and surrounding areas. Will NOT work on adult stages.
  8. Soil drenches containing the botanical insecticide pyrethrin are somewhat effective, but should only be used as a last resort.

Tip: If possible, wait until the soil has warmed before planting tubers. Larvae prefer cool soils and dig deeper into the ground when temperatures rise.

Wireworm Control: How To Get Rid Of Wireworm Pests

Wireworms are a major source of grief among corn farmers. They can be very destructive and difficult to control. While not as common in the home garden, learning more about the control of wireworms and how to get rid of wireworm pests in the event they do pop up is your best line of defense. Let’s find out what are wireworms in the garden.

What are Wireworms?

Wireworms are the larvae of what is commonly known of as the click beetle. The click beetle gets its name from the clicking sound it makes when trying to flip itself over from on its back. Wireworms have a very slender, hard body; are yellow to brown in color; and range in size from ½ to 1 ½ inches in length. These pests can cause significant damage to young corn and other plants.

Wireworms take from 2 to 6 years to mature, and larvae will live and overwinter in the soil to depths of 24 inches. When temperatures reach around 50 F. (10 C.), larvae will move closer to the soil surface and return to deep soil again when the temperatures soar above 80 F. (27 C.).

Wireworm Damage

Wireworm damage to commercial corn crops occurs when larvae eat the germ inside the corn kernels. They will eat the entire inside, leaving only the seed coat. Wireworms can also tunnel into parts of the roots or stems of young plants causing stunted growth and wilted leaves. Other crops that can be damaged by wireworms include barley, potatoes, wheat and clover.

Damage is most likely to occur when the plants are young and the weather turns cold, causing seed germination to slow down. Wireworm infestations are also found in areas of the crop field that retain a great deal of moisture.

How to Get Rid of Wireworm Pests

Wireworm control involves taking a soil sampling for wireworms or inspecting the soil after plowing in the fall.

Dry flour baits can be inserted into the soil using a corn planter. Twenty-five baits should be put out per acre, and these traps should be checked every couple days. If the bait stations have at least two or more wireworms each, crop damage is possible.

In the home garden, chunks of potatoes can be set in the ground with a skewer as a decoy trap. The skewer should be pulled out with the potato once a week and thrown away with the larvae.

While several insecticides are labeled for wireworm control and applied prior to or at the time of planting, there are no treatments once these pests have infected crops. All infected plants should be removed from the garden and disposed of immediately upon identification. Check with your local county agent for a list of wireworm insecticide pre-treatments.

The long-lived, hungry wireworm can wreak havoc on the agricultural sector. With a diverse choice of common crops as their target, these click beetle larvae seek out and chew through the roots of plants.

These pests are notoriously hard to kill off. Many chemical alternatives don’t seem to have much effect.

Don’t let this scare you, though! Today we learn what a wireworm is. We’ll also go over the adult form, the click beetle. And while it may take some work to get rid of these soil pests, I’ll give you a list of options that will help you wipe them out.

My Top Products To Get Rid of Wireworms:

  • PyGanic
  • Safer Brand Yard & Garden Spray
  • EcoSMART Organic Insect Killer Granules
  • Beneficial Nematodes
  • Yard Butler TNT-4 Garden Twist And Tiller

Wireworm Overview

Common Name(s) Wireworm, click beetle, elaters, snapping beetles, spring beetles, skipjacks, potato worm
Scientific Name(s) Multiple species in the Elateridae family
Family Elateridae
Origin Worldwide, most commonly in crop-growing regions
Plants Affected Agricultural crops and grasses. Commonly impacts corn, wheat and other cereal crops in addition to brassicas, root crops like carrots, potatoes, beets and sweet potatoes, climbing plants like beans and cowpeas, trailing plants like melons, and an assortment of others such as onions, lettuce, and strawberry.
Common Remedies Pyrethrin sprays, insect killing granules, crop rotation, tilling the larvae to the soil surface, trapping, using beneficial nematodes to help control soil pests.

Life Cycle Of Wireworms

Gulf Wireworm as an adult click beetle. Source: Keith Roragen

The adult stage of this pest is called a click beetle. Click beetle is a name which refers to the clicking sound the adults make when snapping their thorax. These click beetles are the only stage of the wireworm life cycle which can be regularly seen above ground. Keep a watchful eye out for these!

Click beetles lay their eggs directly in the soil. These eggs are tiny and white, round in shape, and usually are placed near grass or crop roots. When they hatch, the larvae emerge, which are what we call wireworms . Larvae coloration is usually yellow to black.

Click beetle throughout its life cycle. Source: Bugldy99

Roughly 1/16th of an inch in size, the newly hatched larvae will grow to reach sizes of 3/4″ in length before pupation. This process can take 2-3 years, as wireworms are slow to develop. While they are not particularly damaging to plants in their first year, the older larvae can devour the roots of plants, causing wilting and plant death.

The pupae that are developed at the end of the 2-3 year larval stage are white and extremely soft. These are easily damaged by anything that might dig into the soil. When the pupal stage ends, the adult click beetle will dig back to the surface and begin the life cycle again.

Common Habitats

As wireworms spend their entire larval stage underground, they can be found in, around, or in close proximity to plant roots. Adult click beetles shelter in leaf litter or other plant debris. They prefer to be near their food source.

There are many different species, some of which are named for the environment in which they typically live.

For instance, the Pacific Coast wireworm (Limonius canus) is quite common throughout the west coast region of the US. The dryland wireworm (Ctenicera pruinina) is common in the northwest and western crop growing regions of the US, especially in the plains.

There are varieties of this annoying pest found throughout the world. As this agricultural pest feasts on the roots of predominantly grass or tuber crops, they can be found anywhere where these crops are grown. They are also present in weedy fields where wild grasses provide food sources.

What Do They Eat?

Wireworm on soil. Source: treegrow

While there are types which feast on particular crops, such as the sugarbeet wireworm (Limonius californicus), the vast majority eat the roots of cereal plants and root crops such as carrot, potato, or beet. There’s even a variety referred to as the potato worm because it bores out large holes in tuberous roots.

However, they can be found consuming the roots of brassicas, melons, sweet potatoes, beans, lettuce, corn, onions, peas, and strawberries as well. Some wild grasses that produce seeds, such as ryegrass, can also be a source of food for these pests.

But what do click beetles eat? The adult beetles tend to eat nectar and pollen from flowers. Sometimes they will snack on the flower petals themselves. A few varieties will eat softer-bodied tiny insects like aphids as well.

How To Get Rid Of Wireworms

Common click beetles. Source: gbohne

As I mentioned earlier, it can be notoriously hard to wipe out these guys. This has a lot to do with their soil-dwelling tendencies. It’s hard to find crop worms that you can’t see!

There are some things that you can do to reduce their population and slowly get them out of your soil. Let’s go over those now!

Organic Controls

Click beetles, like most other beetles, are susceptible to pyrethrin-based sprays. If you see click beetles in and around your garden, use a spray such as PyGanic or Safer Brand Yard & Garden Spray. This should take care of the beetles on the surface.

If wire worms have become a problem in your lawn or flower beds, you can use EcoSMART Organic Insect Killer Granules. Kid and pet friendly, these granules will help reduce the population of multiple kinds of insects. These aren’t intended for edible garden use, although they won’t hurt your plants. For lawns or flowers, they’re very effective.

While some people use PyGanic to create a pyrethrin drench for the soil to kill larvae, you should be careful doing so. This can be incredibly effective to reduce larvae populations. However, it can also harm other soil-dwellers who are beneficial to the garden. This should only be done as a last resort during a particularly large infestation.

Environmental Controls

I love to incorporate beneficial insects into my garden, as they often can take care of most pests for me. One of the best possible defenses is to introduce beneficial nematodes into your soil. These extremely tiny organisms will attack and consume the larvae and pupal stages of the pest. They also help with a multitude of other pests!

Place traps in the soil to lure larvae. I particularly like the modified bait trap method shown in the video below. You can also use a large potato that’s been drilled out with a stick through it as a bait potato. Follow the directions in this video to see how it works! If you find lots of worms, then it’s time to move on to more serious control options.

Preventing Wireworms

Cultivate your soil! By tilling your soil, you are bringing all of the larvae to the surface, both active and pupating. This makes them prime candidates for bird food. It also makes the soil less hospitable to crop worm infestation. I recommend using a product such as the Yard Butler TNT-4 Garden Twist And Tiller. This long-handled tiller helps you get deep under the soil’s surface. There are plenty of other options for hand tillers if you’d prefer something else!

Practice crop rotation. It’s important to move your plants around. Keeping them in the same location year after year creates a perfect environment for that crop’s pests to move into. If you change the location of your plant types every year, you can dissuade some types of pest from sticking around.

Frequently Asked Questions

Q: I have some potatoes that have wireworm holes. Are they still edible?

A: Actually, they might be safe to eat. Examine the potato thoroughly. If the only damage was the hole bored through the tuber, and there are no visible signs of rot, you can simply cut out any damaged segments and cook the rest of the potato.

If there are any signs of softening or rot damage around the hole, I would discard the potato. I also do not advise trying to store potatoes with wireworm damage, the same way I would advise against storing potatoes with gouged sides or other external damage.

Q: Can I compost plants with roots that are damaged by wireworms?

A: Well, you can, but it may not be wise to compost the roots. If there are eggs still around the roots themselves, you may be creating a nice warm environment where those eggs could hatch and infest your compost. It’s better to dispose entirely of infested material when possible. The same holds true of any plant which shows signs of disease or pest infestation.

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Lifetime Gardener
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Potato Tuberworm Damage – Tips For Controlling Potato Tuberworms

Okay. What is it? The potatoes you planted were looking green and lush above the soil surface, but underground it’s a different story. Seems someone beat you to the tuber bounty. Upon closer inspection and a little research, at last, a name for this pilferer — the potato tuberworm or Phthorimaea operculella is revealed.

What are Potato Tuberworms?

The question, “What are potato tuberworms” is a little bit more involved than the short answer of “pests.” Commonly found in tropical to subtropical regions, potato tuberworms are actually larvae, or at least it is this stage of the insect that wreaks the most havoc on your spuds.

Potato tuberworm adults are small moths that lay tiny oval eggs of white to yellow hue. Once hatched and full grown, the resulting larvae are caterpillars, which vary in color and feed upon leaves and stems. But, potato tuberworm damage doesn’t end there.

Potato Tuberworm Damage

Most severe potato tuberworm damage results from the larvae eating into the potato tuber at the eyes. More often, the larvae feed under the surface of the spud leaving behind a dark tunnel, but occasionally they also mine deep into the tuber. Either way, the potato tuberworm damage is a hole in the potato that is filled with, well, feces.

Potatoes that are shallowly set or exposed due to cracked soil are those most often assaulted, and the longer they remain in the ground post vine kill, the worse it gets.

Potato Worm Control

Controlling potato tuberworms can be accomplished by trying the following: cultural control, organic/biological control or insecticide treatments.

Cultural control

Cultural practices for potato worm control may include prevention of soil crack with regular irrigation, setting tubers deeply (at least 2 inches deep), prompt harvesting and sanitation of the garden through removal of volunteer plants, crop rotation, clean storage practices, plantation of uninfected seed pieces, and destruction of culling piles.

Any of these practices may reduce the exposure of the potatoes to egg laying female moths, thus reducing potato tuberworm damage and aiding in preventing tuberworms in potato crops.

Organic/Biological control

Controlling potato tuberworms via an organic method of eradication is accomplished utilizing predatory insects like braconid wasps, which kill the larvae by parasitization.

Beneficial nematodes may also be introduced and are an environmentally friendly method of potato worm control. These nematodes seek out and kill soil inhabiting potato tuberworm larvae without harming beneficial insects, such as ladybugs or earthworms. They can be found for sale online.

Insecticide control

When all else fails for potato worm control, there are pesticides that may be applied (with mixed results) to aid in their eradication. If one is attempting to be strictly organic, I have read of the Entrust formulation of spinosad, which may have some good results.

Additionally, the use of pheromone traps can detect potato tuberworm moth activity and help to pinpoint the correct timing for insecticide control. A simple pan of soapy water with a lid for hanging the pheromone bait can be placed among the potato crop in the garden, or a sticky trap may be used to capture the moths.

Insecticide must be used before vine kills or it will have no efficacy. Insecticides for controlling potato tuberworms should be used in the evening during the moths’ most active time and can be found at one’s local garden center.

You should try to utilize cultural methods for preventing tuberworms in potato crops such as irrigation to prevent soil cracks, planting uninfected seed pieces and deep seating of tubers before attempting to use an insecticide for controlling potato tuberworms.

Thought these might help:
http://www.syngenta-crop.co.uk/NR/exeres/5D749023-FE95-4C85-9A85-987D4D63E7A8,frameless.htm
http://www.dgsgardening.btinternet.co.uk/wireworm.htm

HDRA Factsheet (available online to members only):
Wireworm
Often troublesome in newly cultivated ground, wireworms are the larvae of various species of click beetle. The two most common are the garden click beetle, Athous haemorrhoidalis and the common click beetle, Agriotes lineatus. Wireworms attack the underground parts of plants, damaging roots, tubers, corms and stems. Favourites are potato, beetroot and carrot as well as corms and tubers of anemone, dahlia, and gladioli. Damage to roots of strawberries, brassicas, beans, tomatoes and many seeds and seedlings can occur where infestations of wireworm are high.
Typical Symptoms
Damage can occur all year but most damage is in spring and autumn. Damage is often most severe on newly cultivated land, but wireworm larvae may remain in the soil for many years before pupating to adults (see life cycle below).
Tubers and root crops: Small, knitting needle sized entry holes 2-3mm across are seen on the outside of the tuber or root. On cutting open, a network of tunnels may be evident, often invaded and enlarged by other pests such as slugs or woodlice. Further bacterial and fungal rots may develop making them unsuitable for storage.
Corms: Similar damage to tubers above.
Seedlings: Stems are bitten through at or below soil level.
Roots and stems: Roots may show small blackened pits where feeding has occurred; plants may suddenly wilt and die. On fleshy stemmed plants such as tomato and chrysanthemum, wireworm may tunnel into the stems and upwards into the pith. On crops such as maize, stems may be chewed and frayed just above the old seed.
Description of the pest
Wireworm larvae are tough skinned, cylindrical, golden yellow to orange brown in colour and reach up to 25mm in length when mature. Three pairs of thin small legs are located behind the head.
Life cycle
The female click beetle lays her eggs just below the soil surface from May to June, favouring grassland and weedy soil. There may be several sessions of egg laying resulting in a patchy infestation throughout the area. A month later the larvae will hatch and feed on both living and dead plant material in the soil for up to five years. The larvae move through the soil profile in response to changes in moisture and temperature. In warm soils (above 10°C) the larvae feed close to the soil surface. Hotter or much colder temperatures cause the larvae to descend deeper, seeking more favourable conditions. This is why most crop damage occurs in the late spring/early summer, and early autumn. Eventually the larvae construct pupal cells at about 20cm depth in the soil, pupate and emerge during the following summer and early autumn to mate.
Prevention and control
Cultural control: Thorough cultivation, before planting and after harvesting will help to expose the wireworm to natural predators such as birds, frogs, hedgehogs and rove beetles. Remove host grass weeds, where the beetle is known to hide.
Check compost heaps: Expose home-made compost and turf stacks to birds and other predators before use, if they are infested with wireworm.
Harvest early: To limit damage to potatoes and other root crops, lift them early if wireworm is known to be present.
Traps: In infested spots in the garden or greenhouse, place a feeding trap. Spike wire through chunks of raw potato or carrot and bury under the soil surface, approximately 10-14cm down. Best done in spring or autumn, check regularly and destroy any wireworm larvae found.
Bury a pot or net of pre-soaked grain. Wheat or corn are especially useful. Soaking the grain, a day in advance to trapping, promotes seed germination and increases the baits’ attractiveness to wireworm. Cold soils (<10°C) can be warmed up by covering with a sheet of black plastic. Dig up regularly and remove the pest.
Green manure: Growing mustard, Sinapsis alba as a winter intercrop is said to speed up the life cycle of wireworm in the soil, reducing population levels especially in new grassland.
Lois

Potato, Irish-Wireworm

Includes Limonius spp. and Agriotes spp.

Pest description and crop damage Wireworms are the most important soil-dwelling pests infesting crops in the Pacific Northwest. The adults, known as click beetles (Elateridae family), do little or no damage. The larval or immature stages cause major damage to seedlings and the underground portions of many annual crops. The larvae are shiny white at first, but later become straw color or light brown. They look wiry and are about 1 inch long when mature.

Several kinds of wireworms are in the Pacific Northwest. Those causing the most damage in irrigated land are the Pacific Coast wireworm (Limonius canus), the sugar beet wireworm (L. californicus), the western field wireworm (L. infuscatus), and the Columbia Basin wireworm (L. subauratus). Of these, Pacific Coast and sugar beet wireworms are the most common species. Land with annual rainfall less than 15 inches may be infested with the Great Basin wireworm (Ctenicera pruinina). As a result, there may be serious damage when irrigated crops are grown on sagebrush or dry wheat land. This species tends to disappear after a few years of intensive irrigation, but may be replaced by the more serious Limonius spp., which favor moist conditions. West of the Cascade Mountains, other species of wireworms, including Agriotes spp., are pests.

No crop is immune to attack by wireworms, but these pests are most destructive on beans, corn, grain, potatoes, and other annual crops. In potatoes, serious damage results from wireworms tunneling in tubers during feeding. Wireworms damage seed potato after planting, and developing tubers later. Wireworm damage most often is characterized by holes bored directly into the tubers. These holes frequently are healed over, indicating that damage occurred sometime before harvest. Processors have a very low tolerance for wireworm damage and zero tolerance for wireworms in raw product.

Biology and life history Depending on species, wireworms may require two to six years to mature. They overwinter 12 to 24 inches deep in the soil and return near the surface in spring to resume feeding. Mature larvae pupate in the soil, developing into adults that will remain in the soil until the following spring, when they emerge, mate, and lay eggs. Because the female beetles fly very little, infestations do not spread rapidly from field to field.

Soil temperature is important to wireworm development and control. Larvae start to move upward in the spring, when soil temperature at the 6 inch depth reaches 50°F. Later in the season, when temperatures reach 80°F and above, the larvae tend to move deeper than 6 inches, where most remain until the following spring. For more information, see https://catalog.extension.oregonstate.edu/pnw607 and https://catalog.extension.oregonstate.edu/em9166

Scouting and thresholds Ideally, the presence of wireworm in a field should be determined before using control measures. However, effectively determining wireworm density is difficult and/or impractical on the large fields that are the rule in many areas. Crop sequence also is important; thus, planting a susceptible crop such as potatoes immediately after red clover or grain is risky.

In fields that are plowed deeply in the fall, wireworms will turn up during plowing. They may be detected by following behind the plow and checking for them in the turned up soil. Fall plowing, however, is becoming much less common.

There are no established treatment thresholds for wireworms in potatoes. Management decisions are a complex assessment of crop history, scouting, previous pesticide treatments, etc.

Management-cultural and biological controls

Crop rotation is an important tool for wireworm control. Wireworms tend to increase rapidly among red and sweet clover and small grains (particularly barley and wheat). Birds feeding in recently plowed fields destroy many wireworms. However, in seriously infested fields this does not reduce the overall pest population below economic levels. To date, field tests of entomopathogenic nematodes in wireworm infested fields show they do not effectively control wireworms. There are no parasites or biological insecticides known to be effective in wireworm control, but research is ongoing in this area. An important management consideration is avoiding prolonged periods of time between vine death and harvest. Typical wireworm damage occurs mid-season and results at harvest in healed holes in tubers; however, tubers left in the field for weeks after vine death can be re-infested resulting in serious tuber damage and tubers containing wireworms at harvest.

For more information, see

Management-chemical control: HOME USE

  • azadirachtin (neem oil)-Some formulations are OMRI-listed for organic use.
  • zeta-cypermethrin

Management-chemical control: COMMERCIAL USE

See:

Pesticide Tables for Potato Pests

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The research includes field trials to develop effective ways to deliver the Metarhizium biopesticide to wireworms and click beetles.
Photo: Todd Kabaluk/AAFC

An important challenge for Kabaluk is to develop practical, affordable and effective ways to deliver the fungus to the pest. “There are several ways to deliver Metarhizium LRC112 to its targets — wireworms and click beetles,” he says.

“For wireworms, we apply the fungus with a substance that produces carbon dioxide. Carbon dioxide is a powerful wireworm attractant. In nature, it is produced by plant roots and helps wireworms locate the plant root food source. There are many other substances that emit carbon dioxide — rolled oats, for example.”

When the researchers apply the Metarhizium granules plus rolled oats to moist soil, the carbon dioxide emitted from the rolled oats attracts the wireworms to the fungus and they become infected.

Kabaluk also says his colleagues Stefan Vidal, with Georg-August University, and Anant Patel, with the University of Applied Sciences in Germany, have created a very sophisticated granule that is a carbon dioxide-producer and Metarhizium carrier all in one. “It is called Attracap and sold by the German company Biocare. It can be very good at attracting and killing wireworms and protecting potatoes from wireworm feeding damage.” Attracap uses a different strain of Metarhizium brunneum.

Kabaluk’s group is currently experimenting with a variety of attract-and-kill application methods for wireworm control in potato and field vegetable crops, comparing several carbon dioxide-producing options such as rolled oats and Attracap. “At our research centre in Agassiz, B.C., we have some really neat facilities that we use to measure carbon dioxide production of a lot of substances. We use the carbon dioxide production data to choose the substances that will attract the most wireworms.”

To attract click beetles to the fungus, Kabaluk uses pheromones. “Sex pheromones are powerful insect attractants. They are normally emitted by female insects to attract males. Researchers in Hungary have identified and synthesized pheromones from click beetles. These pheromones are ester compounds that happen to be used for other purposes, like creating pleasant scents — the click beetle pheromone esters smell like lemon geranium. Therefore, they are inexpensively purchased from chemical companies,” he says.

The fungal strain also kills click beetles, the adult stage of wireworms.
Photo: Todd Kabaluk/AAFC

However, the commercial pheromones are only available in liquid form. “As I was trying to find a way to attract the beetles to the Metarhizium granules, I realized I needed the pheromone in a solid, granular form. I worked with a small B.C. company that helped formulate some prototype granules.”

The initial test results were very promising. “When the pheromone granules were applied with Metarhizium granules, click beetles literally ran toward their fatal Metarhizium infection. Eighty percent of click beetles were infected in less than three hours.”

The original company has changed ownership, so Kabaluk is now working with another company to refine the product. They are creating long-lasting, weatherproof granules that can be used with the Metarhizium granules.

In addition, Kabaluk and his AAFC colleague, Wim van Herk, are evaluating whether the pheromone granules could be used to cause mating disruption in click beetles. The testing so far indicates that a relatively high rate of the pheromone confuses the males. “They aren’t able to locate the females, meaning there are no male-female hookups, no mating, no egg-laying, and no new wireworms added to the soil,” says Kabaluk.

“Field tests will determine if we can achieve click beetle mating disruption to a degree that will reduce soil wireworm populations.” If this approach is successful, he expects the company they have been working with will likely have a commercial product on the market within a few years.

Kabaluk measures carbon dioxide emissions from different products, such as rolled oats, used to attract wireworms to the Metarhizium biopesticide. Photo: Beth McCannel/AAFC

Another strategy Kabaluk has been exploring is the possibility of applying the fungus as a spray to control click beetles. The advantage with a spray is that it would directly target both female and male beetles. The pheromones only directly attract males to the Metarhizium granules; females are infected only if they happen to randomly encounter the fungus granules.

As part of their work to develop LRC112 as a commercial product, Kabaluk and his group are evaluating it for possible unwanted side effects. “It is required that any pesticide registered for use in Canada be applied according to the instructions on the product label. The label, if necessary, provides instructions on how to avoid impacts on non-target organisms, human health and the environment, given our understanding of the pesticide at the time of registration,” he explains.

For example, they are assessing LRC112’s impacts on beneficial insects. “We’ve carried out several lab tests to determine the effect of Metarhizium LRC112 on beneficial ground beetles and have not really noticed a repeatable negative effect. Of course, at times, some beetles will get infected. Initially, Metarhizium LRC112 would be formulated as a granule and applied beneath the soil . This is not a location where ground beetles would come into contact with the product,” says Kabaluk.

“When we develop it for above-ground use — such as a spray targeting click beetles or with a pheromone to attract click beetles to the fungus granules — we will also expand our testing to determine if ground and flying insects could be affected and, if so, we will develop application techniques to avoid their exposure.”

Looking Ahead

Considering the next steps in the LRC112 research, Kabaluk says there are always a million research questions to answer and problems to solve. “I think first and foremost, Metarhizium LRC112 needs to be registered as a wireworm active ingredient for use in Canada. To do this, AAFC would license Metarhizium LRC112 to a company, preferably a Canadian company, who would act as registrant and product distributor.”

Registering the strain as an active ingredient will open the door for the creation of commercial products derived from it.

Kabaluk’s group will continue their product development work to move LRC112 toward commercialization. “We feel quite confident in the ability of our test products to kill wireworms and protect crops, but we need to formalize application methods and rates so that they are affordable to farmers. As well, we need to create clear instructions for using the products to ensure efficacy,” he says.

“We will also continue testing the ‘host range’ of Metarhizium LRC112, that is, to determine all the wireworm species it will effectively kill. Knowing this will help us plan its expansion for use with other crops, such as grain crops, also vulnerable to wireworms.”

Another area of investigation concerns how the exposure of click beetles to Metarhizium influences their ability to lay viable eggs. “It takes about eight days for click beetles to start dying of a Metarhizium infection, and during that time they have the opportunity to lay eggs. But perhaps Metarhizium affects this ability in some way. Simon Fraser University graduate student Kari Zurowski is studying this subject and has made good progress in understanding it all.”

If funding becomes available, Kabaluk would also like to further explore why sometimes, mysteriously, Metarhizium applications are not quite as effective as expected. “We’ve found evidence that wireworms can be protected from succumbing to Metarhizium infection by symbiotic bacteria, as is the case for many other insects in resisting disease. I’m curious whether the efficacy of Metarhizium could be improved by applying it with an antibiotic .”

Kabaluk’s current Metarhizium LRC112 project is funded by AAFC, many grower associations, small- to medium-sized companies, and farmers, under the Canadian Organic Science Cluster in AAFC’s Canadian Agricultural Partnership Program.

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Posted by Paul Rusnak|April 9, 2012

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Editor’s Note: Much of this information is from a story by Jan Suszkiw of the Agricultural Research Service that was published in the September 2011 issue of Agricultural Research magazine.

Wireworm feeding damage is easy to spot, says Rich Novy, a USDA-Agricultural Research Service (ARS) plant geneticist seeking to shore up America’s $3.3 billion potato crop. The damage resembles a nail hole that has been punched into the spud, pitting its surface and making it less appealing for use in fresh-pack or processing markets.

Organophosphate- and carbamate-based insecticides are available for use against wireworms on potato, among the most commonly used being ethoprop (Mocap, Bayer CropScience). However, the continued registration of some of these insecticides is uncertain, says Novy, who is in ARS’s Small Grains and Potato Germplasm Research Unit in Aberdeen, ID. Plus, the chemicals don’t always eliminate the slender, brownish-orange pests, which as larvae can survive beneath the soil for as long as five years before emerging as adult click beetles.

“That’s part of what makes them so problematic, they are able to just stay in the soil so long,” he says. “That’s why you can get a buildup of wireworms over time.”

South American Aid

Over the last several years, Novy, ARS plant pathologist Jonathan Whitworth, and former University of Idaho associate professor Juan Alvarez, who is now with DuPont, have looked for a solution to the problem in the form of genetic resistance. In particular, they’ve focused the attention on two wild relatives of cultivated potato obtained from Chile and Bolivia: Solanum berthaultii and S. etuberosum. Taking their cue from previous studies showing that the wild potatoes are resistant to Colorado potato beetles and green peach aphids, two disparate pests, the researchers decided to pit the plants against hungry wireworms as well.

To do this, the team crossed germplasm derived from the wild potatoes with a cultivated variety and then selected 15 top-performing plants from three generations of progeny. The researchers’ next step was to plant the progeny lines, called “breeding clones,” in wireworm-infested field plots in southern Idaho and compare the feeding damage they sustained to that of adjacent rows of susceptible Russet Burbank potatoes.

As the researchers had hoped, the resistant clones fared as well as — and sometimes better than — the insecticide-treated Russet Burbank potatoes. “Wireworms are really tough,” says Novy. “Even with chemicals, there isn’t complete control.”

Commercial Availability

At this time, the mechanism of resistance to wireworm has not been determined, but it may be related to glycoalkaloids. These naturally occurring chemical compounds in potato tubers are known to deter some insect pests. Total concentrations of glycoalkaloids in many of the resistant clones are at levels suitable for human consumption, which may open the door to their use in the development of wireworm-resistant commercial varieties.

Novy says they do have a clone, a long, typey Russet, that is derived from its wild relatives, but it hasn’t been tested to confirm that it has wireworm resistance. The potato is in the intermediate stages of development — if it is identified as being wireworm resistant and its agronomic characteristics make it acceptable for release as a variety, then that clone could be available to growers in five to six years. “I’m quite excited by this one clone,” he says. “It needs several more years of evaluations, but it looks promising.”

The team has submitted a paper on their research to the Journal of
Economic Entomology. Novy says that besides wireworm, they are working on resistance to other potato pests such as potato psyllid, to mitigate zebra chip disease, and nematodes, specifically potato cyst nematode and Columbia root-knot nematode, in collaboration with Chuck Brown of USDA-ARS at Prosser, WA.

For more information on the potatoes used in this research, please turn the page

Bank On It

The South American potatoes used in the wireworm research were obtained from NRSP-6, the United States Potato Genebank in Sturgeon Bay, WI. The mission of the NRSP-6 Potato Genebank is to facilitate improvements in the potato of the future by promoting the use of valuable exotic genes found in wild potato germplasm. Small tubers are typical of wild potato species, but they represent a veritable treasure chest of genetic diversity for potentially useful traits that may someday be bred into new varieties. These new varieties must be able to overcome the challenges of pests and stresses with less dependence on chemical fertilizers, insecticides and fungicides. NRSP-6 is doing this through a five-fold approach: acquisition, classification, preservation, evaluation, and distribution of potato germplasm. NRSP-6 is the only federal facility designed to support the germplasm needs of the U.S. potato industry, and it is widely regarded as the most comprehensive collection in the world.

Paul Rusnak is the Senior Managing Online Editor of Florida Grower, American Vegetable Grower, American Fruit Grower, and Greenhouse Grower magazines, all Meister Media Worldwide brands. See all author stories here.

Holes in potatoes have most likely been caused by wireworm. Occurring in all kinds of soil wireworm will attack nearly every kind of crop. They are the larvae or young of beetles commonly known as click beetles of which there are many kinds.
Wireworms are most numerous on land that has recently been cultivated, having previously been grassland. They may attack the sets and sprouts of potatoes but this seldom has a disastrous effect. However serious damage can occur to the tubers as holes made by the wireworm provide access for pests such as slugs, millipedes and other soil organisms. To limit the damage, lift the potato crop as soon as the tubers are mature.
There are no chemical controls for wireworm but it has been found that the risk of attack is much reduced by thorough soil consolidation – the aim should be a firm soil below a firm tilth. Thoroughly cultivating the soil and controlling weeds will also help to eliminate this pest. Digging in the autumn will expose the wireworms to the weather and birds and it is also well worth checking the compost heap before applying to the soil as this can contain large numbers of them.

common name: potato tuberworm
scientific name: Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae)

The potato tuberworm Phthorimaea operculella (Zeller), also known as potato tuber moth or tobacco splitworm, is an oligophagous pest (an insect feeding on a restricted range of food plants) of crops belonging to the family Solanaceae (mainly potatoes , tomatoes , and tobacco ). Phthorimaea operculella has been a minor pest of tobacco for more than 100 years. However, in North Carolina, this pest has emerged as a problem in tobacco plantings over the last five years. This pest has been reported in tropical, subtropical, and Mediterranean agro-zones (Westedt et al. 1998, Flanders et al. 1999, Visser 2005, Golizadeh and Esmaeili 2012).

Figure 1. Damage on a potato inflicted by the potato tuberworm, Phthorimaea operculella (Zeller). Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

The potato tuberworm affects production, reduces quality of the produce, and increases the risk of infection by plant pathogens. The common name potato tuberworm is given to its damaging larval stage. There are two species in different genera with similar names: Tecia solanivora (Povolny) and Symmetrischema tangolias (Gyen). Tecia solanivora (Povolny), the Guatemalan potato moth, is found in Central America and northern South America and attacks potatoes that are still in the field as well as stored potatoes. The Andean or South American potatotuber moth, Symmetrischema tangolias (Gyen), is a pest of stored potatoes in the Andes.

Distribution (Back to Top)

Potato tuberworm is a cosmopolitan pest. In the United States it has been reported in at least 25 states from the Atlantic to the Pacific coast. This pest occurs in most areas where potatoes or other solanaceous plants are grown. It was first recorded in California in 1856 (Alvarez et al. 2005). However, it was not a major concern for growers in the Pacific Northwest until 2002, when severe potato tuberworm damage was documented in a field near Hermiston, Oregon (Rondon et al. 2007). It occurs widely in Africa (Ethiopia, Egypt, Kenya), Asia (Iran, Syria), Europe, Americas (Latin America, Andes of Peru and Bolivia), and Oceania (Australia and New Zealand) (Saour 2004, Vargas et al. 2004, Davidson et al. 2006, Golizadeh and Esmaeili 2012, Golizadeh and Zalucki 2012, Ahmed et al. 2013, Kroschel et al. 2013). Potato tuberworm has been reported in more than 90 countries (Anonymous 2013).

Host Range (Back to Top)

Potato tuberworms are mainly associated with potatoes; however, they have been observed feeding on other plants such as tomatoes, eggplants (Solanum melongena L.), peppers (Capsicum spp.), tobacco, and wild solanaceous plants like Jimson weed or datura (Datura stramonium L.) (Alvarez et al. 2005). In the Pacific northwest, potato tuberworms have only been reported infesting potatoes (Rondon et al. 2007).

Life History (Back to Top)

Eggs, larvae and pupae of potato tuberworm can potentially survive in volunteer potatoes, or in the soil after harvest. Potato tuberworm is known to survive in the soil as pupae. Larval development is interrupted by temperatures below 50°F. Larvae can pupate in the soil, discarded piles of potatoes, dead leaves, on storage walls, or on eyes of stored tubers (Raman 1980). They can also pupate in crevices in walls, floors, and crates.

All instars may occur together in overlapping generations. There are two to eight generations per year depending upon climatic conditions. There are usually two generations per year in temperate climates of North America (Alvarez et al. 2005). In the Northern Hemisphere, peak populations of adults occur from May through June in Israel, from June through August in Yemen, and from April to October in the United States. Generation time can vary from two weeks during summer to seven or eight months if the cycle is interrupted by winter. Winter populations can be active in storage facilities where optimum temperature for survival is maintained. Potato tuber moths can move up to 0.15 miles between crops to infest plants or tubers. Long distance movement of potato tuberworms occurs when infested tubers are accidentally transported (Alvarez et al. 2005).

Eggs: When foliage is not available potato tuberworm moths can crawl a short distance through cracks in loose soil to find a tuber they will use as an oviposition site. In four days, the adult female can deposit 60 to 200 eggs singly or in small clusters directly on host plant parts such as the stem, underside of leaves or in the eye cracks and indentations on tubers. Eggs are smooth, oval, and can be pearly white to yellowish (before hatching) in color. The eggs usually hatch after five days.

Larvae: Larvae are 0.5 to 0.6 inch long, white or yellow with a brown head and prothorax (midsection of the insect body) (Raman 1980, Alvarez et al. 2005). The thorax has small black points and bristles on each segment. The color of larvae changes from white or yellow to pink or green as they mature. The larvae feed on their host plants for up to two weeks before pupation.

Figure 2. Larva of the potato tuberworm, Phthorimaea operculella (Zeller). Photograph by Oregon State University Extension.

Figure 3. Leaf mines caused by the potato tuberworm, Phthorimaea operculella (Zeller). Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

Pupae: Pupae are white, narrow, and 0.5 inch long. Depending upon climatic conditions, pupae take 10 to 30 days to fully develop (Raman 1980, Alvarez et al. 2005). The silken cocoon spun around pupae can become covered with soil and debris.

Figure 4. Late larval instars and pupae of the potato tuberworm, Phthorimaea operculella (Zeller) on a damaged potato. Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

Adults: The moths are narrow bodied, silver grey in color, 0.4 inch long with a wing span of 0.5 inch. Wings are grayish-brown, fringed and elongate with small brown or black markings. Both pairs of wings have fringed edges. At rest, the wings are held close to the body giving the moth a slender appearance. The forewings are yellowish grey with dark spots (2-3 dots on males and characteristic “X” pattern on females); the hind wings are grey (Raman 1980, Alvarez et al. 2005).

Figure 5. The potato tuberworm, Phthorimaea operculella (Zeller) adults. The forewings have 2-3 dark spots on males (right), and a characteristic “X” pattern on females (left). Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

The adults are fast fliers and like most other moths require an insect-collecting net for capturing. These moths live for one to two weeks, are crepuscular (active at dawn and dusk), and feed on nectar. Females are slightly larger than males. Mating begins 24 hours after emergence.

Damage

Larvae feed on potato leaves, stems, petioles, and more importantly potato tubers in the field and in storage. The newly hatched larvae create mines on leaves by feeding on leaf tissue while leaving the upper and lower epidermis of the leaf intact. They prefer feeding on young foliage (Trivedi and Rajagopal 1992). Typical damage results from larvae boring tunnels in tubers. Larvae depositing their excreta make tubers unfit for consumption. Potato tuber eyes become pink due to deposition of silk and excrement by potato tuberworm infestation. Severe infestations result in yield and quality losses during storage where previously infested tubers are stored with healthy potato tubers (Malakar and Tingey 2006, Rondon 2010). This generally destroys the entire crop of stored potatoes.

Figure 6. Damage on potato tuber caused by Phthorimaea operculella (Zeller). Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

Most economic damage occurs to potato tubers in storage conditions in developing countries and is caused by larval feeding. Presence of even one larva is sufficient to spoil and destroy a tuber. Rapidly moving caterpillars penetrate the tubers, form galleries coated with silken threads and eject frass outside the tuber. On leaves, caterpillars form galleries and then penetrate other plant parts. After two to three weeks, caterpillars leave the plant (caterpillars can move through cracks in soil) and pupate on walls of potato bags lying in potato fields. Fungi, bacteria, and mites can develop inside the tunnels made by the larvae, which causes the tubers to rot and emit an unpleasant smell.

Stored crop losses in potatoes ranging from 50% in Yemen and Peru, 86% in Tunisia, Algeria, and Turkey, 90% in Kenya, and 100% in India and the Philippines have been reported (Alvarez et al. 2005). In Egypt, potato tuber moth has caused up to 100% losses to potato plants in fields as well as in storage (Ahmed et al. 2013). Potato tuber moth is also a pest of tomatoes where larvae damage the leaves, stem and the unripe fruits.

Figure 7. Exposed tubers are predisposed to tuberworm damage. Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

Monitoring

Monitoring of potato tuber moth is a critical part of its management. Pheromone traps that attract males have been effective for monitoring potato tuber moth populations. Monitoring is one of the most important components of an integrated pest management (IPM) plan for potato tuber moth. Monitoring gives an indication of insect presence, population and distribution, and allows for timing of pesticide applications for its management. Pan-water traps baited with the pheromone can be used for attracting and monitoring adult male populations. These traps are easy to use and clean between readings. Four traps per quadrant of a circle, about 50 ft from the periphery of the circle are suggested for monitoring in field. No economic threshold level (ETL) has been determined for crop damage or yield loss in fields. However, checking traps twice a week is suggested and pesticide application is recommended in case of high population (e.g., 15 to 20 moths/trap/night) (Anonymous 2013).

Figure 8. Monitoring male adults of the potato tuberworm, Phthorimaea operculella (Zeller) on a pheromone-baited trap. Photograph by Silvia I. Rondon, Hermiston Agricultural Research and Extension Center, Oregon State University.

Management (Back to Top)

The most common method of control of Phthorimaea operculella is pesticides (Dillard et al. 1993). The development of pesticide resistance, resurgence of pest populations, and potential detrimental effects of synthetic pesticides on non-target organisms has led to the adoption of integrated pest management (IPM) strategies. It is important to know the biology and distribution of a pest for an IPM program to be successful.

Field Management
Cultural control
Weeds and volunteer plants can act as alternate hosts for potato tuberworms, and should be eliminated from fields and surrounding areas. Deep planting and good coverage of potato seeds with soil more than 2 inches during hilling helps protect damage by adults and larvae. Discard infested tuber seeds; only use healthy seed tubers for planting. Vines should not be used for covering tubers as they wilt after some time and larvae and moths can penetrate the cover to reach underlying tubers.
Harvest soon after crop maturity. Moth populations are maintained in plant and tuber debris in the field in the absence of main crop. Therefore, timely field cleanliness is an important preventive measure. Cull piles should be destroyed to reduce overwintering stages of potato tuberworm. Avoid leaving harvested tubers overnight in the field as these potatoes could act as egg laying sites for potato tuber moth (Raman 1980, Alvarez et al. 2005, Rondon et al. 2007, Anonymous 2013).
Soil management and irrigation
Irrigation is the most effective preventative method under dry conditions (Raman 1980). Enough irrigation should be provided to not allow cracks to develop deeper than two inches in the soil. It is recommended that fields should be irrigated after vine desiccation to avoid cracks in the soil and that harvest of tubers occurs as soon as the skin sets (Anonymous 2013).
Resistant varieties
Host plant resistance enables plants to avoid, tolerate or recover from pest infestations (Tingey 1986, Panda and Khush 1995). The efficacy of other control methods can be increased using resistant potato cultivars thus reducing use of insecticides (Arnone et al. 1998, Golizadeh and Esmaeili 2012). Rondon et al. (2013) studied potato lines at Oregon, some of which hold promising results for controlling mines and number of larvae in potato tubers. An earlier study was conducted at Oregon by Rondon et al. (2009), and it was confirmed that tubers of the transgenic clone Spunta G2 were resistant to potato tuberworm damage. The resistance germplasm to potato tuberworm is an important part of an IPM program for potato tuberworm.
Biological control
Natural enemies of potato tuber moth can be used as a part of an IPM program. The parasitoids, Copidosoma koehleri and Bracon gelechiae Ashmead (Hymenoptera: Braconidae) have been used with some success in South America and Australia, respectively (Symington 2003, Alvarez et al. 2005).
Bio-pesticides and natural chemicals
Bacillus thuringiensis (Bt) formulations have proved effective for potato tuber moth control in various parts of world (Alvarez et al. 2005).

In several South American countries, PhopGV-based biopesticides (Phthorimaea operculella granulovirus (PhopGV) genus: Betabaculovirus of the arthropod-infecting Baculoviridae) are used to control either Phthorimaea operculella or Tecia solanivora (Zeddam et al. 2013).
Chemical control
Chemical control might be necessary when adults or larvae are present. For chemical recommendations for commercial growers or home gardens, consult your local county Extension service and be sure to follow all local laws regarding pesticide use.

Storage Management
Potato tuberworm is a year-long problem under storage conditions due to continuous breeding of this pest. The length of life cycle of potato tuberworm is highly dependent on temperature. So, storage temperature should always be kept below 52°F. Monitoring in storage situations relies on the use of pheromone traps. Under storage conditions, cultural control options involve elimination of damaged tubers. Screens should be installed at entry points to exclude moths.
Sanitation of storage facility walls, floors, and ceiling is very important. Treat facility with an approved pesticide, if this pest was detected the previous year. Use new or thoroughly sanitized potato sacks, crates or other containers. Bt spray can be used on tubers which are mainly used for human consumption, and pyrethroids on tubers used for seed purpose (Anonymous 2013).

Selected References (Back to Top)

  • Ahmed AAI, Hashemb MY, Mohamedc SM, Shimaa Khalila SH. 2013. Protection of potato crop against Phthorimaea operculella (Zeller) infestation using frass extract of two noctuid insect pests under laboratory and storage simulation conditions. Archives of Phytopathology and Plant Protection. DOI:10.1080/03235408.2013.795356.
  • Alvarez JM, Dotseth E, Nolte P. 2005. Potato tuberworm a threat for Idaho potatoes. University of Idaho Extension, Idaho Agricultural Experiment Station, Moscow, ID. (31 Jan 2014)
  • Anonymous 2013. Potato tuber moth- Tuberworm. CropWatch: Potato Education Guide, UNL Extension. University of Nebraska-Lincoln, Lincoln, NE. (31 Jan 2014)
  • Arnone S, Musmeci S, Bacchetta L, Cordischi N, Pucci E, Cristofaro M, Sonnino A. 1998. Research in Solanum spp. of sources of resistance to the potato tuber moth, Phthorimaea operculella (Zeller). Potato Research 41:39-49.
  • Clough GH, Rondon SI, DeBano SJ, David N, Hamm PB. 2010. Reducing tuber damage by potato tuberworm (Lepidoptera: Gelechiidae) with cultural practices and insecticides. Journal of Economic Entomology 103:1306-1311.
  • Davidson MM, Butler RC, Wratten SD, Conner AJ. 2006. Field evaluation of potato plants transgenic for a cry1Ac gene conferring resistance to potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae). Crop Protection 25:216-224.
  • Dillard HR, Wicks TJ, Philip B. 1993. A grower survey of diseases, invertebrate pests, and pesticide use on potatoes grown in South Australia. Australian Journal of Experimental Agriculture 33:653-661.
  • Flanders K, Arnone S, Radcliffe E. 1999. The potato: genetic resources and insect resistance, pp. 207-239. In: Clement SL, Quisenberry SS (eds.), Global plant genetic resource for insect resistant crops. CRC, Boca Raton, FL.
  • Golizadeh A, Esmaeili N. 2012. Comparative life history and fecundity of Phthorimaea operculella (Lepidoptera: Gelechiidae) on leaves and tubers of different potato cultivars. Journal of Economic Entomology 105:1809-1815.
  • Golizadeh A, Zalucki MP. 2012. Estimating temperature-dependent developmental rates of potato tuberworm, Phthorimaea operculella (Lepidoptera: Gelechiidae). Insect Science 19:609-620.
  • Kroschel J, Sporleder M, Tonnang HEZ, Juarez H, Carhuapoma P, Gonzales JC, Simon R. 2013. Predicting climate-change-caused changes in global temperature on potato tuber moth Phthorimaea operculella (Zeller) distribution and abundance using phenology modeling and GIS mapping. Agricultural and Forest Meteorology 170:228-241.
  • Malakar R, Tingey WM. 2006. Aspects of tuber resistance in hybrid potatoes to potato tuberworm. Entomologia Experimentalis et Applicata 120:131-137.
  • Medina RF, Rondon SI, Reyna SM, Dickey AM. 2010. Population structure of Phthorimaea operculella (Lepidoptera: Gelechiidae) in the United States. Environmental Entomology 39:1037-1042.
  • Panda N, Khush GS. 1995. Host plant resistance to insects. CAB International, Oxon, United Kingdom.
  • Raman KV. 1980. The potato tuber moth. Technical information bulletin 3. International potato center Lima, Peru. (Revised edition 1980)
  • Rondon SI, DeBano SJ, Clough GH, Hamm PB, Jensen A, Schreiber A, Alvarez JM, Thornton M, Barbour J, Dogramaci M. 2007. Biology and management of the potato tuberworm in the Pacific Northwest. A Pacific Northwest. Extension publication. Oregon State University, University of Idaho, Washington State University. (31 Jan 2014)
  • Rondon SI, Hane DC, Brown CR, Vales MI, Dogramaci M. 2009. Resistance of potato germplasm to the potato tuberworm (Lepidoptera: Gelechiidae). Journal of Economic Entomology 102:1649-1653.
  • Rondon SI. 2010. The potato tuberworm: a literature review of its biology, ecology, and control. American Journal of Potato Research 87:149-166.
  • Rondon SI, Brown CR, Marchosky R. 2013. Screening for resistance of potato lines to the potato tuberworm, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae). American Journal of Potato Research 90:71-82.
  • Saour G. 2004. Efficacy assessment of some Trichogramma species (Hymenoptera: Trichogrammatidae) in controlling the potato tuber moth Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae). Journal of Pest Science 77:229-234.
  • Sharaby A, Abdel-Rahman H, Moawad S. 2009. Biological effects of some natural and chemical compounds on the potato tuber moth, Phthorimaea operculella Zell. (Lepidoptera: Gelechiidae). Saudi Journal of Biological Sciences 16:1-9.
  • Sisay A, Ibrahim A. 2012. Evaluation of some potential botanicals to control potato tuber moth, (Phthorimaea operculella) under storage condition at Bako, western Ethiopia. eSci Journal of Plant Pathology 01:14-18.
  • Symington CA. 2003. Lethal and sublethal effects of pesticides on the potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae) and its parasitoid Orgilus lepidus Muesebeck (Hymenoptera: Braconidae). Crop Protection 22:513-519.
  • Tingey WM. 1986. Techniques for evaluating plant resistance to insects, pp. 251-284. In: Miller JR, Miller TA, Berenbaum M (eds.), Insect Plant Interactions. Springer, New York, NY.
  • Trivedi TP, Rajagopal D. 1992. Distribution, biology, ecology and management of potato tuber moth, Phthorimaea operculella (Zeller) (Lepidoptera: Gelechiidae): a review. Tropical Pest Management 38:279-285.
  • Vargas B, Rubio S, López-Avila A. 2004. Estudios de hábitos y comportamiento de la polilla guatemalteca Tecia solanivora (Lepidoptera: Gelechiidae) en papa almacenada. Revista Colombiana de Entomología 30:211-217.
  • Visser D. 2005. Guide to potato pests and their natural enemies in South Africa. Arc- Roodeplaat Vegetable and Ornamental Plant Institute, Pretoria, South Africa.
  • Westedt AL, Douches DS, Pett W, Grafius EJ. 1998. Evaluation of natural and engineered resistance mechanisms in Solanum tuberosum L. for resistance to Phthorimaea operculella Zeller. Journal of Economic Entomology 91:552-556.
  • Zeddam J-L, Lèry X, Gómez-Bonilla Y, Espinel- Correal C, Páez D, Rebaudo F, López-Ferber M. 2013. Responses of different geographic populations of two potato tuber moth species to genetic variants of Phthorimaea operculella granulovirus. Entomologia Experimentalis et Applicata 149:138-147.

Potato Pests

University of Kentucky College of Agriculture

The local market for potatoes from Kentucky has resulted in increased interest in the crop by potential growers. Growing a new crop often means dealing with a different pest complex. This publication was prepared to provide information on the biology, identification and control of potato pests. More on specific information on insecticides is available from ID-36, “Commercial Vegetable Crop Recommendations”.

Soil Insects

Soil insects, primarily wireworms and white grubs, can severely damage seed pieces and tubers. These insects feed on grass roots and should be considered as a serious threat when potatoes are to be grown in ground immediately following sod.

Figure 1. Wireworm damage leaves holes in tubers.

In these situations, a pre-plant broadcast application of a soil insecticide should be considered. For best results, treat after soil temperature at the six inch depth has reached 50°F. By this time soil insects should be active and nearer the surface.

Figure 2. White grubs produce large holes in tubers.

The threat of damage by soil insects is lessened with time out of sod. Because some wireworms and grubs spend two or more years in the soil a problem may still occur. A planting-time soil treatment should be sufficient in these cases.

Above-Ground Pests

Colorado Potato Beetle

The common black and yellow-striped “potato bug”, a very familiar insect, is the most serious pest of potatoes. Both the adult, or beetle, and the black-spotted, red larva feed on potato leaves. Their damage can greatly reduce yield and even kill plants.

Figure 3. Colorado potato beetle has alternating black and white stripes on its wing covers.

In addition to potato, Colorado potato beetle can be a serious pest of tomato, eggplant, and pepper. Colorado potato beetle overwinters in the soil as adults. The Colorado potato beetle is a yellow insect with alternating black and white strips down its back. They become active again in the spring and feed on weeds and volunteer on early-planted potatoes. They will even enter the soil to attack emerging foliage. Female beetles lay batches of about two dozen orange-yellow eggs on the underside of the leaves. Each female can lay 500 or more eggs over a four to five week period. The eggs hatch in four to nine days and the larvae begin to feed on potato foliage. The larvae are humpbacked with two rows of black spots. The larvae usually feed in groups and damage can be severe. The larval stage lasts two to three weeks.

Full grown larvae move to the ground and change into an inactive or pupal stage. In five to 10 days the new adult beetles emerge. This insect can go from egg to adult in as little as 21 days. They feed for a few days, before egg laying begins. There are two full and occasionally a partial third generation each year. If foliar sprays are used, an effort should be made to treat after most eggs have hatched but before serious plant damage occurs.

This insect is notorious for development of resistance to insecticides over short periods of time. A rotation among different classes of insecticides is recommended to discourage resistance. There is a new commercially available strain of Bacillius thuringiensis (var tenebrionis) that are effective against small larvae (less than 1/4 inch) and should be applied at egg hatch or when larvae are first seen. A premature treatment may lose much of its effectiveness before the eggs hatch. An insect growth regulator, called Align, has also been released for control of this insect. It is an extract of the neem seed that prevent the insect from developing normally.

The Colorado potato beetle, Leptinotarsa decemlineata, can be easily confused with its close cousin the false potato beetle, Leptinotarsa juncta. While these two insects look nearly identical, only the Colorado potato beetle is a serious pest. While the adult false potato beetle has alternating black and white strips on its back as well, one of the white strips in the center of each wing cover is missing and replaced by a light brown strip. The eggs are slightly larger and fewer found in a cluster. The humpbacked larva is similar, but with only one row of dark spots on each side. False potato beetles are frequently found feeding on some solanaceous weeds, such as horsenettle, but do no growth and reproduction occurs when feeding on potato.

Figure 4. In some years aphids can be problematic.

Aphids

Winged aphids may move into potato fields in significant numbers. These migrants settle on the leaves and begin to remove plant sap. During this period they are also capable of producing large numbers of wingless aphids that in turn place an even greater stress on plants.

Distorted leaves and “sticky” leaf surfaces are signs of aphid infestation. Natural enemies and diseases can often keep aphid populations under control. Limiting the use of broad-spectrum insecticides will conserve predators and parasites that help keep aphid populations under control.

Potato Leafhopper

Potato leafhoppers are wedge-shaped, 1/8-inch long, green, active insects. They use their piercing-sucking mouthparts to remove sap from the potato leaf. These small insects fly readily. Because of their small size and habit of feeding on the underside of the leaf, they are easily overlooked.

Figure 5. Potato leafhopper migrates from southern overwintering areas each summer.

The symptom of leafhopper activity is more apparent – a triangular brown spot at the tip of the leaf. Similar triangles may appear at the end of each lateral veinlet or the entire margin may roll upward as though scorched. These symptoms are known as “hopperburn”. Other conditions may produce similar symptoms. Check the underside of leaves for the tiny leafhoppers to confirm that they are the cause of the problem.

Potato leafhoppers do not overwinter in Kentucky. Winds carry them into the state each year from the Gulf Coast. They generally appear between May 25 and June 5. Within a few days after mating, females lay their eggs in the stems and larger leaf veins of succulent plants. The eggs hatch in about 10 days into the immature or nymphal stage. The light green, wedge-shaped nymphs are smaller than the adults and do not have wings. Both stages are very active. Adults jump or fly readily when disturbed while the nymphs run sideways across the leaf and over the edge.

Development from egg to adult takes about three weeks in warm weather. Very large leafhopper populations can build up in a short time during the summer.

Occasional Pests

A variety of other insects may be numerous at times. Control decisions should be based on the extent of the infestation in the field and the severity of damage.

Figure 6. Blister beetles can attack a variety of vegetables.

Blister beetles are narrow, elongate insects. They may be found feeding in clusters on potato leaves. Infestations are usually localized within fields and treatment of an entire field is seldom necessary. Rarely do blister beetles do enough damage damage to cause any yield loss.

Hornworms are easily identified and will feed on potato foliage. These worms can consume large amounts of foliage but severe infestations are not likely to occur. Hormworms can easily be controlled using any of the insecticides containing Bacillus thuringiensis var kurstaki. Rarely do hormworms cause losses to potato yields.

Figure 7. Flea beetles leave characteristic small round holes in leaves.

Flea beetles cause the small shot-hole damage to leaves. These tiny beetles overwinter as adults and may appear in fields very early in the season and cause serious damage to young plants. Sevin provides very good control of flea beetles when they are numerous on small plants.

Systemic Insecticides

Planting time use of systemic insecticides allows protection against moderate levels of soil insects plus activity against leaf-feeding pests such as aphids, leafhoppers and flea beetles. Insecticidal effects are generally greatest during the early part of the growing season. Read the label thoroughly and observe pre-harvest intervals carefully.

Foliar Sprays

A variety of insecticides may be used on potatoes to control insect pests. Repeated sprays may be needed in some years, especially against late season pests. See ID-36, “Commercial Vegetable Crop Recommendations” for recommendations.

Colorado Potato Beetle Resistance Management

The Colorado potato beetle is notorious for its ability to rapidly develop resistance to insecticides that are used repeatedly to control it. This has been a serious problem on the east coast for some time, and is becoming more of a problem in Kentucky. With a more limited number of available insecticides, some homeowners feel they have exhausted their control options.

Resistance develops more rapidly to an insecticide when that insecticide is used repeatedly as the only control measure. Often over use of one insecticide may favor the development of resistance to other insecticides in the same chemical class. Insecticides in the same chemical class usually have the same mode of action, i.e. the same method of killing the insect. Consequently, to delay or prevent resistance it is important to avoid repeated usage of one particular insecticide by rotating the insecticides used. Rotation needs to be among different classes of insecticides.

Other control measures such as hand picking of adult beetles and immature stages will also aid to delay the development of resistance. Resistance by Colorado potato beetles should be managed on a field-to-field basis. While they may be resistance to one insecticide in a particular field, those in other fields within the same county may not have developed resistance to that insecticide.

Revised: 11/19

CAUTION! Pesticide recommendations in this publication are registered for use in Kentucky, USA ONLY! The use of some products may not be legal in your state or country. Please check with your local county agent or regulatory official before using any pesticide mentioned in this publication.

Of course, ALWAYS READ AND FOLLOW LABEL DIRECTIONS FOR SAFE USE OF ANY PESTICIDE!

Photos courtesy Ric Bessin, University of Kentucky Entomology

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