Potato, Irish-Wireworm, Pacific Northwest Pest Management Handbooks

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.

Management-chemical control: HOME USE

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

Management-chemical control: COMMERCIAL USE

pnwhandbooks.org

Wireworm Woes: Identify, Prevent, and Control These Pests

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:

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

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.

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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?

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

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.

www.epicgardening.com

POTATO PESTS AND DISEASES

If potatoes are grown on the same land season after season this will also encourage pest and disease. Rotate the growing of potatoes on a three, or four yearly cycle. Always buy seed potatoes from certified suppliers.

POTATO BLIGHT


Leaf which has potato blight

For more information on Potato Blight check out our comprehensive article on how to identify and treat potato blight.

COMMON POTATO SCAB

The signs of infection are not visible above ground, it’s only seen on the potato tuber itself when you harvest. The potato will will have raised, rough brown bumps on the skin, some cases of infection are worse than others. Infected potatoes are still edible and the quality and taste of the flesh is exactly the same as normal. Simply peel the potato as normal and you will remove almost all of the raised bumps leaving you with a perfect potato.

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Common scab occurs mainly where water is scarce when the potatoes are developing. This is the key to avoiding the problem — aim to keep developing tubers in a moist but well drained soil. Lots of well rotted organic matter (the stuff on your compost heap) dug into the soil at planting time is the first line of defence. Watering the soil well when conditions are dry is also a good idea.

There are no chemical solutions to scab so if it’s common in your area stick to potato varieties which have a good level of resistance to scab such as Golden Wonder, Arran Pilot and King Edward.

Common Scab is made far worse if the soil is alkaline so definitely do not add lime to the soil for at least a year before planting potatoes in it.

POTATO SLUG DAMAGE


Slug Damage

Normally with slugs they can be killed by the use of slug pellets but the slugs which damage potato tubers remain almost exclusively below ground so slug pellets on the surface have little effect. Trying to kill the slugs with chemicals is, possibly with one exception (see next paragraph), a waste of time. The best measures are preventative as follows:

  • Choose varieties resistant to slug attack such as Charlotte, Estima, Golden Wonder, Kestrel, Romano, Sante and Wilja.
  • If the problem is widespread grow early varieties which are not in the ground long enough for slugs to be a problem.

  • Do not manure the ground before planting which encourages slugs, use blood, fish and bone as a fertiliser instead.
  • Lift potatoes as soon as possible, slug damage normally starts at the beginning of August.
  • The one exception which may work is an old gardener’s trick. Place one slug pellet below each potato set when they are planted. I have no conclusive evidence if this works or not but from the experience of fellow gardeners it does seem to have a significant effect.

    Slugs and snails will also eat potato leaves leaving the edges ragged and often holes in them. They tend to affect the lower leaves more than the the upper leaves. We find that they rarely cause enough damage to do anything about them. Slug pellets or environmentally friendly solutions can be found on the internet.

    POTATO BLACKLEG

    Click here for our detailed article on how to identify Potato Blackleg and what can be done to prevent and treat it.

    POTATO EELWORM

    They are difficult to diagnose but the key symptoms are yellowing of the leaves, general poor growth and small tubers. The only way to confirm this very common pest is to dig up affected potatoes and examine the roots with a magnifying glass or microscope. Potato eelworm do NOT eat into potato tubers, they feed on the roots alone. If you have holes in your potatoes suspect slug or cutworm or wireworm (see below) damage. Click here for our detailed article on potato eelworm.

    POTATO WIREWORM

    COMMENTS / QUESTIONS LEFT BY OUR READERS

    Sometimes our readers ask specific questions which are not covered in the main article above. Our
    Potato comment / question and answer page
    lists their comments, questions and answers. At the end of that page there is also a form for you to submit any new question or comment you have.

    www.gardenfocused.co.uk

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    Extension Entomology—please call
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    Wheat Insects

    Head of wireworm larva showing wedge-shaped profile.

    Wireworms are the larval stage of click beetles. Larvae are slender and shiny, yellow to brown, with six slender, short legs. Mature larvae range from 1/2 to 1 inch long. Problems are worse in loose or sandy soils that facilitate larval movement. Larvae orient to the smell of germinating seeds and will often follow the drill row, consuming seed as they go. Larvae of some species may take four or more years to complete development. Generations often overlap, with a wide range of larval sizes present in the same field. The only real treatment option for wireworms is seed treatment, either on initial planting if there is a history of wireworms in the field, or when replanting due to wireworm injury. Seed commercially treated with imidacloprid (Dyna Shield Imidacloprid, Gaucho, Gaucho Grande, Gaucho XT, Imida, Raxil MD-W and Senator) or thiamethoxam (Cruiser) generally provides acceptable control of wireworms. Follow label directions on rates, application method and safety precautions. Do not feed treated seed or contaminate grain not being used for seed. Also note that some products may restrict grazing after planting treated seed.

    Please refer to the most recent version of the Wheat Insect Management Guide for control options.

    entomology.k-state.edu

    Features Agronomy Diseases
    New tools to battle wireworm

    2018 saw fewer problems with wireworm in Atlantic Canadian potato fields than past years, according to Christine Noronha, a research scientist for Agriculture and Agri-Food Canada based in Prince Edward Island. But this doesn’t mean the problem has gone away.

    January 14, 2019 By Julienne Isaacs

    “Producers using rotation crops saw less [wireworm] damage this year,” Noronha says.

    In general terms, researchers are cautious about predicting wireworm damage. Of all potato pests, wireworm has proven one of the most difficult to understand. New research highlights the complexity of wireworm behaviour and the attendant difficulty of controlling the pest in the field. As few chemical controls are registered in potato against wireworm, an integrated pest management (IPM) approach is essential.

    IPM forms the backbone of Noronha’s program. This past summer, her team worked with P.E.I. producers on a study combining two methods of wireworm control – NELT (which stands for Noronha Elaterid Light Trap) traps to control adult female click beetles, and mustard or buckwheat rotation crops to target the larvae.

    “I asked the farmers to leave two 1.5-foot strips unplanted up the entire length of the field. We installed 30 NELT traps in each strip for a total of 60 traps in a 50-acre field,” she explains. All trapped female and male beetles were removed from the field once a week during May and June, which is their activity period. The field was planted with brown mustard. Next year, potatoes will be planted in the same fields, and Noronha and her team will collect samples to evaluate damage to tubers.

    “We’re catching females in the traps, which prevents the laying of eggs, but by using the rotation crop we are trying to control the larvae as well,” Noronha explains. “The two methods combined may give us reduction in damage for a longer period.”

    Wireworm population in the field is the biggest problem confronting researchers and producers, Noronha says.

    “There seems to be little correlation between bait trap numbers and damage,” she says. “Often, we’ll put out our baits and think, ‘we don’t have a problem,’ and then we see damage.”

    Producers don’t know how many bait traps to put out, or the optimal time of year for placing them in the field, she says. “We don’t know much about the movement of wireworms in the soil, so I’m looking at horizontal and vertical movement of wireworms in the laboratory and the field.”

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    In a lab study looking at horizontal wireworm movement, Noronha’s team found that wireworms in the larval stage can easily move about 3.6 metres in 24 hours to reach bait traps; by 48 hours, 50 per cent of wireworms in the study had reached the bait. The team also found that when bait traps were placed at 2.4 and 2.6 metres respectively, wireworms would reach the first trap, start to feed on the bait and then move to the second bait before the food was depleted.

    “Even if there’s food available, they’ll still move on. If you remove your bait after seven days and you’ve captured seven individuals, there might have been 10, with three moving on to a different food source sometime before the bait was removed. So that means we can never be sure what the population is,” Noronha says. Her goal is to use this information to find the ideal length of time to leave bait in the ground.

    Another field study ran in 2017-2018 looking at horizontal movement of wireworms. Noronha’s team put tubes in the ground to a depth of 80 centimetres in October and watched the wireworms move down through the soil as it froze. In the spring, 90 per cent of the wireworms had returned to the surface to start feeding by mid-May. This means early to mid-May is a good time to put out traps for monitoring, she says.

    Noronha’s team will continue to work on developing ways to better predict wireworm populations.

    AAFC research biologist Todd Kabaluk is leading the Organic Science Cluster for wireworms for the next five years.

    Kabaluk’s research focus is on biological controls for wireworms. One promising method uses entomopathogenic fungi, which kills insects by infecting them through the exoskeleton, to target wireworms in the larval stage. He’s working with the private sector to develop a control product using a virulent fungal pathogen that he discovered as the active ingredient: Metarhizium brunneum strain LRC112.

    Field results have shown a 75 per cent reduction in wireworm feeding damage to potatoes using granular formulations, Kabaluk says.

    Kabaluk is also working on a spray formulation for click beetles, the adult stage of wireworms, which can be used in rotation years and on headlands where beetles emerge. The treatment is specific to click beetles and has so far proven to be relatively easy on beneficial insects.

    He’s also developing another application technique for the biocontrol that uses an “attract and kill” method: a pheromone is deployed to attract click beetles to a biocontrol band laced with Metarhizium, which slowly kills the beetles over a period of days.

    To make this system work, Kabaluk invented pheromone granules; previously, pheromones for click beetles had only been available in liquid form. He’s working with a Costa Rican company, ChemTica, to develop them.

    In studies using the pheromone granules, 80 per cent of the beetles picked up a Metarhizium infection three hours after application, he says.

    Pheromone granules have other potential applications; one of them is mating disruption. Kabaluk is collaborating with AAFC research scientist Wim Van Herk, who is currently investigating how the granules can be used to emit a sex pheromone to confuse male beetles and disrupt their ability to find females.

    “We have pheromones that will be effective against the most pestilent invasive wireworm species on both the east and west coast – those in the genus Agriotes,” Kabaluk says.

    Van Herk, who has continued Bob Vernon’s research program, says pheromones are a key aspect of wireworm research. “Every species has its own unique pheromone. But we don’t have pheromones yet for the native species of wireworm in Canada. They’re unknown,” he says. “So that’s another project I’m working on – trying to identify, in collaboration with a pheromone chemist, what the pheromone structures are of the native species.”

    Van Herk is working on another project in both British Columbia and P.E.I. using pheromones to trap adult click beetles in spring, as a monitoring technique. He’s currently developing a risk assessment guide for producers that will help them evaluate wireworm risk based on factors including the number of click beetles in traps, field history and damage to neighbouring fields.

    Biological controls are emerging as a key growth market when it comes to insect pests, including wireworms. According to Kabaluk, the growth rate of biopesticides is about 15 per cent per year as large companies merge with the small- to medium-sized enterprises that have traditionally specialized in biological controls.

    “There’s an acceleration in research and development for biopesticides, so I can see them becoming more mainstream pesticides in the future.”

    It’s a much-needed advancement, particularly for the organic sector, for which there are currently few products registered against wireworm. Any new affordable and efficacious product for conventional producers would be welcomed, whether it is biological or chemical, according to Kabaluk.

    Van Herk’s team is conducting an efficacy study across Canada, testing different compounds for use against wireworm in potato. His team has also done studies in wheat, which can be used to help control wireworm in potato in two different ways.

    “You can use wheat treated with insecticide either as a rotation crop – if you can eliminate your wireworms in cereals then the following year you have a clean field as far as wireworms go – or you can use treated wheat as an in-furrow application in between your tubers.”

    Using the latter method, Van Herk’s team found damage control between 70 and 80 per cent when the broad-use insecticide Fipronil was used on wheat planted in potato rows. Fipronil is not registered in Canada, but the team is attempting to find another insecticide that is equal in efficacy.

    In terms of insecticide options, producers can use Thimet 20G, an organophosphate systemic insecticide, against wireworm in potato. The product is restricted, so producers who want to use it have to complete a certification and licensing requirement.

    According to Andrew Dornan, a senior field development representative for Bayer CropScience Inc., the company currently has one product registered for wireworm in potato – Titan, a second-generation neonicotinoid insecticide. “What we’ve found, particularly in P.E.I., which is really struggling with a species that’s hard to control, is that if we do combinations of Titan as a seed treatment and bifenthrin (Capture insecticide) as an in-furrow, they’re getting control of wireworm that is equal to use of Thimet,” Dornan says. However, Capture has been scheduled for a three-year phase-out ending in 2021.

    BASF has also launched a new Group 30 insecticide, Broflanilide, and anticipates registrations in Canada and the United States. The insecticide has seen good performance as a cereal seed treatment for wireworm control.

    “Wireworm needs a lot of research attention right now,” Kabaluk says. Producers may have to wait several years for research to translate into products that work in the field against this difficult pest – but promising results on many fronts mean there is hope on the horizon.

    www.potatoesincanada.com

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