Flea Beetles — Brassica — Ontario CropIPM

Brassica

Flea Beetles

Beginner

Scientific Name
Phyllotreta sp.

All of the cruciferous crops grown in Ontario are susceptible to the damage caused by flea beetles.В There are several species of flea beetles that attack crucifers. By far, the majority of these are crucifer flea beetles. Striped flea beetles make up about 10% of the population. They are capable of destroying enough foliage on seedlings to kill the plant. While all crucifers are attacked by these beetles, they prefer the non-waxy, ethnic crucifers.

Identification

  • Small (2– 3 mm, 1/12- 1/8 in.) shiny black beetles
  • Adults are active and jump when disturbed
  • Feeding damage consists of numerous “shot-holes,” 1– 5 mm (1/25- 1/5 in.) in diameter
  • At the seedling stage, flea beetle feeding can kill the plant

Period of Activity
Adult flea beetles overwinter in leaf litter. They emerge and begin feeding on young plants in mid-May. Eggs are deposited near the roots of host plants throughout the spring and early summer. Larvae develop on the roots. In late July, adults emerge from the soil, feed and then seek hibernation sites in the fall. Cold and/or wet spring and early summer temperatures tend to keep damage pressure of this pest low.В

Scouting Notes
Inspect 25 randomly selected plants throughout the field. Since flea beetles are active and will jump away when disturbed, observations should be made when approaching the plant. Record the number of beetles on each plant and divide by 25 to get an ‘average’ number of beetles per plant. A damage assessment of the shot-hole injury typical of adult feeding should also be taken into consideration due to the rapid movement of the flea beetle on a plant.

Thresholds
Up to the 6-leaf stage, plants can tolerate no more than 1 flea beetle per plant. After this stage, feeding will not interfere with plant growth. Feeding damage at later stages may have an impact on marketability and crop quality.

Advanced

Scientific Name
Phyllotreta sp.

All of the cruciferous crops grown in Ontario are susceptible to the damage caused by flea beetles.В There are several species of flea beetles that attack crucifers. By far, the majority of these are crucifer flea beetles. Striped flea beetles make up about 10% of the population. They are capable of destroying enough foliage on seedlings to kill the plant. While all crucifers are attacked by these beetles, they prefer the non-waxy, ethnic crucifers.

Identification
The most common flea beetle attacking crucifers in Ontario is the crucifer flea beetle, Phyllotreta cruciferae. They are small, 2- 3 mm (1/12- 1/8 in.) long, shiny black beetles, with enlarged hind legs.В Adults are active and jump when disturbed. Striped flea beetles, Phyllotreta striolata are brownish-black with yellow stripes down their backs.

On cabbage, broccoli and cauliflower, flea beetles prefer the younger leaves.В Typical damage consists of numerous ‘shot-holes’ 1- 5 mm (1/25- 1/5 in.) in diameter.В Older feeding holes may be ringed with brown, dried leaf tissue, while fresh feeding holes have green edges.В Numerous black or brown pellets of frass can be found scattered throughout the feeding area.В Damage can be especially severe if the insects feed on the growing point of the plant. At the seedling stage, flea beetle feeding can kill the plant.

Biology
Flea beetles in Ontario have one generation per year.В Adult flea beetles overwinter in leaf litter and emerge early in the spring, around the middle of May.В They feed initially on cruciferous weeds, volunteer crops and canola, and move in large numbers to cruciferous crops as they emerge.В Eggs are deposited near or sometimes on the roots of host plants. Once hatched, larvae develop on the roots. Pre-pupal and pupal stages develop in the soil in an earthen cell. In late July, adults emerge from the soil, feed for a time and seek hibernation sites in the fall. The lifecycle from egg to adult may take as little as 7 weeks, making a second generation possible in some years.

Period of Activity
Adult flea beetles emerge early in the spring, around the middle of May and deposit eggs throughout the spring into early summer. The season’s newly emerged adults feed into the fall before seeking hibernation.

Weather plays a large role in flea beetle activity. Warm, dry conditions accelerate flea beetle development and the appearance of the new generation of adults, whereas cold spring and/or high rainfall in May or June tend to reduce the severity of damage and economic loss.В

Scouting Notes
Inspect 25 randomly selected plants throughout the field. Since flea beetles are active and will jump away when disturbed, observations should be made when approaching the plant. Record the number of beetles on each plant and divide by 25 to get an ‘average’ number of beetles per plant. A damage assessment of the shot-hole injury typical of adult feeding should also be taken into consideration due to the rapid movement of the flea beetle on the plant.

Flea beetles tends to prefer to attack plants and foliage exposed to bright sunlight such as seedlings, isolated plants, or plants in widely spaced rows. Shade seems to inhibit their activity.

Thresholds
Up to the 6-leaf stage, plants can tolerate no more than 1 flea beetle per plant.В After this stage, the leaf surface is great enough that feeding will not interfere with plant growth.В However, excessive feeding damage at any time leaves wounds where disease may enter.В If black rot is present in the field, flea beetles may spread the disease. Control may be necessary because the threat of this disease is much greater than the threat of feeding damage.

Management Notes

  • Early plantings may be protected with row covers.
    Transplants are less susceptible to damage than direct-seeded crops.
  • Beetles tend to prefer specialty crucifers over traditional brassica crops.
  • In Ontario, flea beetles have been adequately controlled in cabbage, cauliflower and broccoli with the use of a trap crop, Indian mustard (Brassica juncea var. crispifolia).В The trap crop should be planted up the drive rows.
  • The beetles are attracted to these plants when they are placed as far as 60 rows apart.В They can be transplanted at the same time the crop is put in the field.В
  • It is not necessary to spray the trap rows, but uncontrolled feeding may reduce their effectiveness if flea beetles destroy too much of the foliage.В
  • Take care to ensure that the Indian mustard does not go to seed.В
  • The beetles are attracted to the Indian mustard even when the plant is mature and prefer this trap crop to the extent that they will usually not build up to threshold levels in the surrounding crop.В
  • Unfortunately in ethnic crucifer production systems the trap crop method has not been successful. The beetles appear to prefer the ethnic crucifers as much as the trap crop.В

www.omafra.gov.on.ca

Flea beetles

Quick facts about flea beetles

How to identify flea beetles

Flea beetles are a type of leaf beetle in the family Chrysomelidae.

Most adult flea beetles are very small (1/16 –1/8th inch long). An exception is the spinach flea beetle, which is 1/4-inch long.

  • Flea beetles can be black, bronze, bluish or brown to metallic gray.
  • Some species have stripes.
  • All flea beetles have large back legs which they use for jumping, especially when disturbed.

The most common flea beetles in Minnesota gardens are:

Most flea beetles feed on very specific plants, but the palestriped flea beetle (Systena blanda) feeds on a variety of plants, like, squash, beans, corn, sunflowers, lettuce, potatoes and many weeds.

Life cycle of flea beetles

Flea beetles live through the winter as adults in leaf litter, hedgerows, windbreaks and wooded areas.

Adult flea beetles become active in early spring. Depending on the species, females lay single or clusters of eggs in small holes, in roots, soil or leaves of many vegetables as well as occasionally on flowers and ornamental shrubs and trees.

Small white larvae hatch from eggs and feed on the roots of the newly planted seedlings.

Larvae then transform into pupae in the ground. There are usually one to two generations per year.

Damage caused by flea beetles

All types of flea beetles cause similar damage.

Adult flea beetles cause the most damage by feeding on the leaves and stems. They create shallow pits and small rounded, irregular holes (usually less than 1/8th inch) in the leaves. This type of damage is unique to flea beetles.

Plants started from seeds are less tolerant of feeding damage compared to transplants, but both can be severely injured if flea beetle numbers are high.

The larvae usually cause little to no damage to the plants (with the exception of potato flea beetle larvae).

How to protect your plants from flea beetles

Flea beetles are most damaging in spring. It is important to monitor for their activity as soon as seedlings have emerged.

  • Place yellow sticky traps in your garden to see if you have flea beetles.
  • Check your plants for flea beetles and their damage.
  • Prevent severe damage to your plants by treating seedlings when there are more than five flea beetles per plant.
  • Protect your crops if 10-30% leaves on seedlings and transplants have dropped off.
See also:  Bark Beetles Are Decimating Our Forests

It is generally not necessary to treat flea beetles during summer, especially at the end of the season. By summer, crops reach the 4- or 5-leaf stage and are strong enough to survive feeding damage. The number of adult flea beetles also goes down at that time.

Cole crops (cabbage, broccoli and cauliflower) and other plants with edible greens can be damaged later in the summer. Monitor and treat them as needed.

Make gardens unwelcoming to pests

Control weeds in and around planting sites to limit food sources for flea beetles.

  • Remove old crop debris so that beetles will not be able to get protection in the winter.
  • Plant crops as late as possible. Plants grow faster in warmer temperatures and are more stable to resist damage from flea beetles.
  • Keep flea beetles out of the vegetable crop

    • Use row covers or other screening to keep beetles out, when the seedlings are growing.
    • Remove row covers before the flowers come up so pollinating insects can reach the plants.
    • Plant a highly-favored crop, such as radish, as a trap crop, before you plant your main crop.
      • Adult flea beetles will be attracted to the tallest, earliest crops available.
      • Once beetles are actively feeding on the trap crop, spray with a labeled pesticide.

    Natural enemies can control flea beetles

    Microctonus vittatae is a native braconid wasp (found more commonly in the eastern half of the U.S). This wasp kills the adult flea beetle. The larvae of this wasp develop on the female flea beetle and prevent the beetle from reproducing.

    Using pesticides

    There are many pesticides labeled for treating flea beetles. Below are names of active ingredients that are commonly available in pesticides sold in stores that sell garden pesticides:

    • pyrethrins/pyrethrum
    • carbaryl
    • malathion
    • spinosad
    • permethrin
    • lambda cyhalothrin
    • cyfluthrin

    CAUTION: Mention of a pesticide or use of a pesticide label is for educational purposes only. Always follow the pesticide label directions attached to the pesticide container you are using. Remember, the label is the law.

    Be sure that the vegetable you wish to treat is listed on the label of the pesticide you intend to use. Also be sure to observe the number of days between pesticide application and when you can harvest your crop.

    extension.umn.edu

    Vegetable Insects

    FLEA BEETLES

    Rick E. Foster and John L. Obermeyer, Extension Entomologists

    If you want to view as pdf, click here

    Several species of flea beetles are common in Indiana, sometimes causing damage so severe that plants die. Flea beetles are small, hard-shelled insects, so named because their enlarged hind legs allow them to jump like fleas from plants when disturbed. They usually move by walking or flying, but when alarmed they can jump a considerable distance.

    Most adult flea beetle damage is unique in appearance. They feed by chewing a small hole (often smaller than 1/8 inch) in a leaf, moving a short distance, then chewing another hole and so on. The result looks like a number of “shot holes” in the leaf. While some of the holes may meet, very often they do not. A major exception to this characteristic type of damage is that caused by the corn flea beetle, which eats the plant tissue forming narrow lines in the corn leaf surface. This damage gives plants a greyish appearance.

    Typical flea beetle damage
    (Photo Credit: John Obermeyer)

    Flea beetles lay their eggs on plants or in soil around the base of plants. The tiny larvae feed on the roots of the plant, doing only minor damage to edible crops. Generally, flea beetles are not difficult to control, but often they will have already seriously injured crops before they are detected or the extent of damage is realized. Therefore, it is very important to regularly check susceptible plants, especially when they are in the seedling stage. Most species of flea beetles emerge from hibernation in late May and feed on weeds and other plants, if hosts are not available. In Indiana, some species have multiple generations per year, and some have only one. Keeping fields free of weed hosts will help reduce flea beetle populations. Flea beetle damage often can be observed on weed hosts before it becomes apparent on crops. Also, flea beetles tend to become more numerous when susceptible crops are grown in the same area year after year. Therefore, for commercial growers, crop rotation may help reduce flea beetle damage.

    Corn flea beetle damage on corn leaf
    (Photo Credit: John Obermeyer)

    FLEA BEETLES FOUND IN INDIANA

    Flea Beetles Found in Indiana. a) Potato Flea Beetle: Epitrix cucumeris (Harris); b) Corn Flea Beetle: Chaetocnema pulicaria (Melsheimer); c) Grape Flea Beetle: Altica chalybea (Illiger); d) Red-Headed Flea Beetle: Systena frontalis (Fabricius); e) Sweet Potato Flea Beetle: Chaetocnema confinis (Crotch); f) Palestriped Flea Beetle: Systena blanda (Melsheimer); g) Striped Flea Beetle: Phyllotreta striolata (Fabricius); h) Spinach Flea Beetle Disonycha xanthomelas (Dalman)
    (Photo Credit: John Obermeyer)

    Potato Flea Beetle is black and 1/16 inch long and is one of the most common and destructive flea beetles, attacking potatoes, tomatoes, green pepper, eggplant, and other solanaceous plants. Adults emerge from the soil in mid-spring and feed on young foliage of these crops. They also may feed on sunflower, morning glory, jimson weed, and lambsquarter. Larval feeding on potato tubers may cause roughness, pits, and trails on the surface or in the tuber itself. These pits show up as black spots on peeled potatoes. Potato flea beetles are also vectors of several diseases of potato.

    Spinach Flea Beetle is easily recognized and is the largest of our common species. It is almost 1/4 inch long, has dark, greenish-black wing covers, a yellow-orange thorax, and a dark head. Unlike other species, the spinach flea beetle lays its eggs in clusters on leaf surfaces. Larvae feed on the undersides of leaves. In addition to spinach, adults will feed on beets, chickweed, lambsquarter, and many other weeds. There are usually two generations of spinach flea beetles per year, the first developing on weeds and the second developing on spinach and beets.

    Striped Flea Beetle commonly attacks cruciferous plants such as cabbage, broccoli, turnip, radish, and mustard in most areas of Indiana. It will also feed on shepherdspurse, wild mustard, and other weeds. The adult is shiny black, about 1/12 inch long, with a longitudinal, wavy yellowish stripe on each wing cover. Injury done by the adults appears as pits or holes in the leaves. Larvae may seriously injure the roots of plants, particularly turnips and radishes.

    Palestriped Flea Beetle feeds on cabbage, beans, tomatoes, corn, peas, strawberries, and other crops. Weed hosts are ragweed, pigweed, and lambsquarter. The adult is about 1/8 inch long but ranges in color, from shiny reddish to brownish-yellow. A straight, broad, yellow stripe runs down each wing cover.

    Sweetpotato Flea Beetle is common in the southernmost parts of Indiana. The adults are small (only about 1/16 inch long), bronze-black with yellowish legs and antennae. Feeding damage by the adult sweetpotato flea beetle is somewhat different than other species. Feeding injury on early sweet potato foliage, appears as narrow grooves in the upper and lower leaf surfaces. Badly damaged leaves turn brown and die. Adults also may feed on morning glory and other plants. By mid-June they have usually left the sweet potatoes to lay their eggs near the roots of bindweed.

    Red-headed Flea Beetle is about 1/6 inch long and dark black with a reddish-yellow head. It feeds on cabbage, beans, beets, and potatoes, as well as many weeds.

    Mint Flea Beetle is about 1/12 inch long, pale brownishyellow, with a darker brown head and black eyes. The larvae, which are the primary damaging stage, feed in the soil on roots. Feeding by the adults, which is usually not serious, may cause leaves to dry up and fall from the plants, especially in hot years. Commercial mint producers may use malathion at 1-1/2 pints per acre after cutting and removal of crop from the field for control of adults to prevent oviposition. The 7-day harvest restriction should be observed if applied before cutting.

    Grape Flea Beetle is almost 1/5 inch long and dark, shining steel-blue. They feed on the developing buds of grape vines in late April or early May, often causing considerable injury. The eggs are laid under bark on the vines. After hatching, the brown larvae with black spots, feed extensively on the leaves. Larval damage resembles that done by corn rootworm beetles. After feeding 3-4 weeks larvae drop to the ground and pupate in the soil. In 1-2 weeks, the new adults emerge and feed for the remainder of the summer before going into hibernation.

    Corn Flea Beetle is a black, pinhead-sized (about 1/16 inch) insect that feeds on all types of corn. It can be a serious pest when growing conditions are poor and plants are making slow growth. Damage is generally confined to plants less than 6 inches tall. Corn flea beetle feeds by stripping the green top layer from the leaves, resulting in irregular brown or grey lines. Most importantly, corn flea beetle can transmit a bacterium that causes Stewart’s wilt.

    Stewart’s wilt
    (Photo Credit: John Obermeyer)

    Discolored growing point in diseased plant
    (Photo Credit: John Obermeyer)

    Sweet corn varieties vary greatly in their susceptibility to Stewart’s wilt. Contact your seed dealer to purchase varieties with resistance to Stewart’s wilt.

    Overwintering flea beetles suffer significant mortality during cold winters. To determine the potential for wilt problems in your area, add the average monthly temperatures (В°F) for December, January, and February. If the sum of these three numbers is less than 90, then the disease is not expected to be serious. If the sum is between 90 and 100, then epidemics of moderate severity are possible. If the sum is greater than 100, there is a high probability that the disease will be severe. In fields where a susceptible variety is grown, check them on a regular basis if moderate or severe disease pressure is expected, based on winter temperatures. Usually, growers in southern Indiana can expect more serious problems than growers in the northern part of the state.

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    CHEMICAL CONTROL

    Most plants can tolerate considerable flea beetle feeding. However, younger plants could be killed, and older ones may suffer from water loss and reduced photosynthetic capability. See ID-56, Midwest Vegetable Production Guide at https:// ag.purdue.edu/btny/midwest-vegetable-guide/Pages/default.aspx for insecticide recommendations for vegetable crops. For grapes, see the Midwest Fruit Pest Management Guide at https://ag.purdue.edu/hla/Hort/Pages/sfg_sprayguide.aspx. Home gardeners should see E-21 Managing Insects in the Home Vegetable Garden at https://extension. entm.purdue.edu/publications/E-21/E-21.pdf.

    READ AND FOLLOW ALL LABEL INSTRUCTIONS. THIS INCLUDES DIRECTIONS FOR USE, PRECAUTIONARY STATEMENTS (HAZARDS TO HUMANS, DOMESTIC ANIMALS, AND ENDANGERED SPECIES), ENVIRONMENTAL HAZARDS, RATES OF APPLICATION, NUMBER OF APPLICATIONS, REENTRY INTERVALS, HARVEST RESTRICTIONS, STORAGE AND DISPOSAL, AND ANY SPECIFIC WARNINGS AND/OR PRECAUTIONS FOR SAFE HANDLING OF THE PESTICIDE.

    It is the policy of the Purdue University Cooperative Extension Service that all persons have equal opportunity and access to its educational programs, services, activities, and facilities without regard to race, religion, color, sex, age, national origin or ancestry, marital status, parental status, sexual orientation, disability or status as a veteran. Purdue University is an Affirmative Action institution. This material may be available in alternative formats.

    This work is supported in part by Extension Implementation Grant 2017-70006-27140/ IND011460G4-1013877 from the USDA National Institute of Food and Agriculture.

    extension.entm.purdue.edu

    Insect Pests of Sweet Corn

    Factsheet | HGIC 2205 | Updated: Feb 7, 2019 | Print | Download (PDF)

    Cutworms

    Cutworms damage a few plants in most gardens every year, but some gardens are so heavily infested as to warrant control by the grower. Bottom land (low-lying land, creek bottoms, etc.) is most frequently the site of damage, although fields that are neither bottom land nor well-drained land commonly have cutworms.

    Black cutworm (Agrotis ipsilon) and damage to young corn stalk.
    Frank Peairs, Colorado State University, www.insectimages.org

    Several cutworm species (Agrotis ipsilon, Peridroma saucia, Feltia ducens) are involved, but those that feed just above the soil surface or just beneath it cause most of the injury. In either case, the top of the plant is severed from its roots, and the larva (caterpillar) that did the cutting may usually be found curled up in the soil close to the stub of the cut plant, within 2 inches (5 cm) of the surface. Most species move from plant to plant on successive nights, while some remain to feed on the roots and underground stem of cut plants.

    All cutworms pass the winter as partly to fully-grown larvae (caterpillars) in the soil or under trash or clumps of grass. They start feeding in the spring and continue growth until early summer. They enter the soil to become pupae (the non-feeding stage where the larva changes to an adult form). They emerge as moths during the summer. The moths are grayish or brown “millers” that are attracted to lights in the spring and summer. Each female moth lays about 1,000 eggs on the ground or on foliage in grassy or weedy fields. The eggs hatch and the young larvae feed on roots and foliage of grasses and weeds, hibernate and attack whatever vegetation is present the following spring. The larvae are hairless, plump, soft-bodied caterpillars that vary in color and markings. All have huge appetites.

    Cutworm damage can often be avoided by not planting on newly broken sod or on land that was grassy or weedy the previous summer. In addition, home gardeners can place a collar of stiff paper, cardboard, or aluminum foil around each plant for protection after transplanting to the garden. At the first sign of cutworm moths, spray the plant stems and leaves with Bacillus thuringiensis (B.t.) to kill the larvae. A bait can be made by mixing a B.t. suspension with bran until the liquid is absorbed by the bran, and then adding a small amount of molasses. Crumbled pieces can be scattered around the base of the plants to protect them. Cultivating the soil can kill cutworms.

    Seed-Corn Maggot

    On sunny days in early spring, many small flies are often seen darting about, hovering or resting on posts, fences, implements, surface trash or the ground. These are probably the adults of the seed-corn maggots (Delia platura).

    Seed-corn maggot adults (Delia platura) appear similar to small houseflies.
    Pest and Diseases Image Library, www.insectimages.org

    Eggs are laid on the soil surface where there is an abundance of decaying vegetable matter. The eggs hatch and the larvae (maggots) feed and develop at temperatures as low as 40 °F (4 °C). Injury is usually most severe in wet, cold seasons and on land high in organic matter. The maggots feed on many forms of vegetable matter present in the spring. They are most noticeable when corn fails to germinate or produces weak seedlings due to the maggots feeding in the kernels. Full-grown yellowish-white maggots are about 1/4-inch (6 mm) long, sharply pointed at the head end, legless and very tough skinned.

    Injury can be avoided by planting late enough to get quick germination of seed, especially if soil is rich in organic matter. If damage does occur, prompt replanting will usually result in a good stand, because of quicker germination.

    Southern Corn Rootworm

    This insect is often called the corn budworm (Diabrotica undecimpunctata howardi), which in South Carolina more accurately describes its habits than the name rootworm. It is not usually found in the roots and as a rule does not feed on them, as is the case with rootworms found elsewhere. This insect eats directly into the heart or bud of the plant, right above the base of the stalk. This causes the bud leaves to wilt and die.

    Southern corn rootworm larva (Diabrotica undecimpunctata howardi) and damage to base of shoot.
    University – USDA Cooperative Extension Slide Series, www.insectimages.org

    Several insects injure corn seedlings in such a way that suggests a “budworm” caused the damage. Only by pulling up the plant and examining it carefully can the proper diagnosis be made. If the southern corn rootworm is suspected, look on the base of the stalk for a clean-cut round hole about 1 /32 inch (.8 mm) in diameter. No other corn pest makes such a hole. If one is found, cut into the stalk or examine the soil for a thin, soft-bodied, ivory-colored larva (immature form) with a brown head and a brown disc on the last body segment.

    The adult corn rootworm is the familiar spotted cucumber beetle, which overwinters in protected spots, flies about whenever the temperature reaches 65 °F (18 °C) or above, and feeds on nearly any growing crop or weed during the early spring. Winter legumes are especially attractive to the beetles. On warm days between January 1 and April 15, eggs are laid in the soil near where the adults have fed.

    The adults are attracted to gardens that have an abundance of certain plants and generally avoid clean, bare land. The best way to avoid injury is by turning under cover crops at least 30 days before planting corn or keeping gardens free of weeds for 30 to 60 days before planting. This practice largely eliminates the threat of injury by larvae that hatch from eggs laid near these other plants. Late planting also helps avoid injury from this insect but may result in increased damage by other species.

    Southern corn rootworm adult (Diabrotica undecimpunctata howardi).
    J.P. Michaud, Kansas State University, www.insectimages.org

    Tobacco wireworm larvae (Conoderus vespertinus).
    R.J. Reynolds Tobacco Company Slide Set, R.J. Reynolds Tobacco Company, www.insectimages.org

    Wireworms

    Tobacco wireworm adult – “click beetle” (Conoderus vespertinus).
    Natasha Wright, Florida Department of Agriculture and Consumer Services, www.insectimages.org

    Although several species of wireworms are found in South Carolina vegetable gardens in the spring, only two are serious pests of sweet corn. The tobacco (or corn) wireworm (Conoderus vespertinus) eggs are laid in the summer. They hatch into larvae that feed on the roots of a variety of plants. The wireworm overwinters as a larva. When sweet corn is planted in this field the following spring, the wireworms feed on the kernels and cause poor germination and stunted, spindly, sickly plants that often die or are nonproductive.

    Pupation (the process whereby the larva transforms to a nonfeeding form before transforming into the adult) occurs in the soil, and the new adults, known as “click beetles.” emerge during early summer. They may be found hiding in terminal buds of weeds and crop plants or down in the whorl of young corn. The adults lay eggs during June from which larvae hatch.

    Damage varies from year to year, but some injury occurs every year. Some years there are widespread outbreaks and then many years may pass without damage being reported. Sand wireworms (Horistonotus uhlerii) overwinter as larvae but feed on both the kernels and the roots. Plants over 2 feet (61 cm) high stop growing, turn yellow, wilt on hot days and die. During this period they are easily pulled out of the ground because most of the roots have been severed. Over two dozen sand wireworms may be found per hill of corn in a heavily infested field. Surviving plants do not yield normally. Pupation occurs during May, eggs are laid from June 15 to July 15, and the tiny larvae feed for a while on the roots of various plants but cause no damage to the mature crops.

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    Home gardeners can use various measures to control wireworms. Trap wireworms in pieces of potato scattered around the garden, rotate crops and plow or cultivate infested soil in late summer or in autumn to kill or expose various insect stages to predators.

    Corn leaf aphid (Rhopalosiphum maidis) infestation.
    Department of Plant Pathology Archive, North Carolina State University, www.insectimages.org

    Corn Leaf Aphid

    Corn leaf aphids (Rhopalosiphum maidis) on sweet corn are generally of minor importance in South Carolina. Occasionally conditions will favor the build-up of aphid populations over part of a field. The population peak usually occurs soon after tassel formation. Aphid feeding results in stunted and deformed tassels, development of black mold on the aphid honeydew (a sugary material excreted by aphids as they feed on plant sap) on the leaves and silk, and poor pollination and grain development. About this time, their natural enemies become established and the aphid population rapidly falls off. Corn leaf aphids are vectors of Maize dwarf mosaic virus. Some varieties of corn are more susceptible than others to leaf aphids.

    Corn Flea Beetle

    The corn flea beetle (Chaetocnema pulicaria) has a black, oval-shaped body, tinged with bronze or bluish green. They overwinter in litter and trash around fields. In early spring, beetles are active on weeds and then move to corn seedlings during May through June. Infestations are more severe when a cold spring follows a mild winter. Corn flea beetles are vectors of Bacterial Wilt of corn.

    Adult beetles leave numerous, small, circular feeding holes and bleached out spots or stripes on the corn leaves. Such direct feeding is insignificant unless large numbers of beetles attack slow-growing corn, especially during a cold spring.

    Keep areas around the garden clean and free of plant debris and weeds to reduce overwintering sites. Late planting of corn may help reduce flea beetle damage.

    Corn flea beetle adult (Chaetocnema pulicaria).
    University of Illinois at Urbana-Champaign Archive, University of Illinois at Urbana-Champaign, www.insectimages.org

    Corn flea beetle (Chaetocnema pulicaria) damage.
    University of Illinois at Urbana-Champaign Archive, University of Illinois at Urbana-Champaign, www.insectimages.org

    Corn Earworm

    Late season corn earworm larva (Helicoverpa zea).
    Whitney Cranshaw, Colorado State University, www.insectimages.org

    Corn earworm (Helicoverpa zea) is the most common of the sweet corn insects, being found in all areas of South Carolina. Infestations are generally uniform throughout the state. In untreated plots, up to 90 percent of the ears can be expected to show feeding signs. Eggs are laid on the leaves when the plants are small. The caterpillars go down into the whorl to feed, and by the time this injury is first seen, most of the damage has been done and the worms are covered by a plug of frass (a sawdust-like waste) which protects them from parasites and insecticides. Injury to the foliage occurs before tasseling. The corn leaves are ragged when they grow out, but this damage usually does not seriously affect the crop. Late-planted corn is likely to be severely damaged, for the egg-laying adults become more numerous as the season progresses.

    The new generation of moths lays eggs on fresh corn silk as it appears. Usually several eggs are laid on the silk of each ear, but only one worm reaches maturity due to natural enemies and cannibalism. Ears having tight husks extending well beyond the tip of the ear are least injured since feeding may be completed in the silk channel. Larvae cut a small hole at the side of the ear, through which they emerge. They drop to the ground and enter the soil to transform to pupae (the nonfeeding stage where the larva changes to an adult).

    Corn earworm moths (Helicoverpa zea).
    Clemson University – USDA Cooperative Extension Slide Series, www.insectimages.org

    All of the damage caused by corn earworms is not direct. The indirect damage occurs when other insects and disease organisms use the earworm holes as entrance sites. The resulting damage often exceeds that caused by the earworm.

    The adult moths have a wingspan of about 1½ inches (3.8 cm). They vary in color, being usually light tan-brown, marked with dark gray, irregular lines and a dark area near the tip of the wing. Hind wings are light tan with a dark band near the margin. Moths are often found in the daytime resting in the whorl of young corn or at the base of the leaves of older corn. Each female may lay from 1,000 to 3,000 eggs. Larvae vary in color from a light green or pink to nearly black, though most individuals are brownish green. Usually alternating light and dark stripes run the length of the body. The eyes are yellowish orange with an inverted “Y” between them. Mature larvae are about 1½-inches (3.8 cm) long.

    To control this pest, plant corn as early as possible and apply mineral oil on corn silks five to six days after silk emergence. Mixing a Bacillus thuringiensis (B.t.) product with mineral oil can improve control of earworms. With liquid B.t. products, use a ratio of 1 part B.t.to 20 parts oil. One application of ¼ teaspoon or five drops of the oil mixture should be applied to the silk at the tip of the ear. Alternatively, insecticides may be used for control. Thoroughly wet the silks with insecticide, and repeat until ears are harvested. Select tight-husked corn varieties, as this trait inhibits corn earworm movement into the ear. Varieties that show resistance to damage are Country Gentleman, Stay Gold, Victory Golden, Silver Cross Bantam, Golden Security and Silvergent.

    Fall Armyworm

    This insect is present during most years, but occasionally the fall armyworm (Spodoptera frugiperda) is extremely numerous. The larva feeds on corn foliage, stalks and ears, entering the base of the ears, feeding along the sides of the ears and even tunneling into the cob. It usually emerges near the base of the ears, leaving round holes 3 /16 inch (4.8 mm) in diameter in the shucks.

    Fall armyworm (Spodoptera frugiperda) and damage to corn ear.
    University of Georgia Archive, University of Georgia, www.insectimages.org

    This insect, unable to overwinter in South Carolina, must fly here from much farther south. When moths emerge from the ground, they fly a considerable distance before laying eggs. Gardens covered with grass are chosen, and the larvae consume great quantities of food. If the appetite of the worms is still unsatisfied when all grass has been eaten, they start to eat the crop. After the crop is consumed, they mass together and crawl or “march” in search of other crops. When mature, they enter the soil to become pupae, seeming to suddenly disappear. The moths emerge about two weeks later and fly off to plague another section of the country.

    Since South Carolina sweet corn is usually mature by the time this pest arrives in great numbers, it is not injured. However, if corn is planted late or the insects come early, they catch the corn at or just before the milk stage and cause severe damage. The leaves may be stripped from the stalk and the ears so thoroughly damaged that no corn is harvested. Cold, wet weather in the spring favors insect development and suppresses its natural enemies. Furthermore, gardens are usually grassier in cold, wet years and thus attract the moths for egg laying.

    The adult fall armyworm is a moth about 1½ inches (3.8 cm) across the wings. The forewings are dull, mottled, brownish gray, while the hind wings are pinkish white edged with a smoky-brown line. The dark-eyed larva is about 1½-inches (3.8 cm) long when mature. It is variable in color from light brown to nearly black and has several narrow lines down the back and sides. It feeds during the daytime, in contrast to larvae of related species which leave the plant to hide, coming back to feed at night.

    The fall armyworm can be effectively controlled only while the larvae are small. Early detection and proper timing of an insecticide application are critical. Early planting is the most effective cultural control method in the south.

    European Corn Borer

    A telltale sign of injury from European corn borers (Ostrinia nubilalis) appears as broken tassels caused by the borers feeding in the tassel stems. Much frass (sawdust-like waste) is pushed out of the burrows. Later in the season their presence is indicated by small, round holes at any location on the stalk. In either case, the point of entrance is usually marked by a protruding mass of white frass that accumulates at the base of the leaves. The tunneling within the stalks weakens them so that plants break over. Feeding on the shank of the ear causes it to fall to the ground. The larvae (caterpillars) also feed on the developing kernels or tunnel into the cobs.

    The adults are strong-flying moths with yellowish-brown wings marked with wavy dark lines. Eggs are laid in groups on corn leaves, and the young larvae of the first generation feed on foliage before boring into the stalk. The larvae are flesh-colored, faintly spotted caterpillars, about ½- to 1-inch (1.27 – 2.54 cm) long. There are about three generations a year in South Carolina. The winter is passed as full-grown larvae in the stems where they have been feeding, especially those close to the ground.

    hgic.clemson.edu

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