Soybean Insect Pests

North Carolina Cooperative Extension Service

See Also: Scouting Soybeans (North Carolina Agricultural Extension Service publication AG-385) and Insects and Related Pests of Field Crops (Publication AG-271), available through the county Agricultural Extension Service office.

Introduction

Numerous kinds of insects occur in soybeans. Most are beneficial or harmless, but some can cause yield loss and even crop failure if not controlled.

Yield-reducing insect populations do not occur with enough regularity to allow a grower to accurately predict when and where treatment will be needed. Pest insect populations can be vastly different from year to year, from area to area, and from variety to variety. As a result, soybeans must be scouted (checked for insects) at intervals throughout the growing season.

The treatment of soybeans with chemical insecticides should only be done on a treat-as-needed basis. Overtreatment is expensive and polluting, and may lead to future insect problems. Also, mistimed treatments can lead to severe insect infestations later in the same season. These conditions also support the need to scout soybeans to detect insect problems and to time applications properly.

"Soybean Insect Pests" provides the scout with a brief description of the damaging stage, a designation of size-range and a picture of the common pests. A scout will encounter many nonpest insects not covered in this booklet.

When identification of these insects is desired, specimens may be sent to the Plant Disease and Insect Clinic at North Carolina State University. Correct procedures for collecting specimens to be identified are presented in the North Carolina Agricultural Chemicals Manual or can be obtained from your county extension office. Persons outside North Carolina can usually have specimens identified by extension entomology specialists at their respective agricultural colleges.

Foliage Feeders

Foliage-eating insects are present in practically all soybean fields throughout the growing season. Most fields suffer no yield loss since the number of foliage feeders usually remains at low to moderate levels. Many studies have indicated that soybean plants compensate to a large extent for loss of or damage to foliage. Younger plants which have not begun to bloom or to fill pods can tolerate greater foliage damage than plants which are fruiting.

Soybean farmers and scouts should be aware of damage limits recommended by the Agricultural Extension Service to determine correctly if soybeans should be treated for foliage feeders. These thresholds are available from the county extension office.

Green cloverworm (Plathypena scabra)

Greenish caterpillars with faint white strips along the body. Sometimes the stripes are not obvious. They have four pairs of prolegs and move with a looping motion similar to the soybean looper. When disturbed, these larvae become very active and fall to the ground.

Damage. Green cloverworms only eat foliage. They make holes in the leaves and are damaging only under very high populations or in combination with other defoliators. They are present throughout most of the growing season.

Picture of Green Cloverworm

Soybean looper (Pseudoplusia includens)

Light green in color with several thin light lines running the length of the body. The body of this caterpillar is largest at the rear and tapering to the head. Loopers form the characteristic hump or "loop" when crawling. There are three pairs of prolegs.

Damage. Loopers eat large holes in the leaves and, under high populations, can strip an entire field. Economic infestations of this pest seldom occur before late August or early September. This pest usually occurs in fields that have been previously sprayed.

Picture of Soybean Lopper

Velvetbean caterpillar (Anticarsia gemmatalis)

Greenish, brown, or almost black caterpillars with a broad lighter band down each side. Head is prominent and usually yellow or orange. Caterpillars have five pairs of prolegs with the last pair having the appearance of a forked tail. When disturbed, they wiggle violently.

Damage. This caterpillar eats the entire leaf and will strip whole fields when high numbers are present. Pods sometimes will be attacked when defoliation is severe. Damaging populations usually do not occur before September and are limited to late-planted fields, especially double-crop soybeans.

Picture of Velvetbean Caterpillar

Beet armyworm (Spodoptera exigua)

Olive-green to near black, velvety smooth caterpillar with a stripe down each side. Two black spots are present on the second segment, and there are five pairs of prolegs. Larvae fall and curl up when disturbed. Small larvae web the leaf underside.

Damage. Beet armyworm is chiefly a pest of late-planted seedling soybeans. Small larvae skeletonize the lower leaves. Large larvae feed over the whole plant. Severely damaged plants are very ragged in appearance.

Picture of Beet Armyworm

Mexican bean beetle (Epilachna varivestis)

Adults are copper to yellow rounded beetles with 16 black spots on their backs. Larvae are yellow, oval, soft-bodied, grublike insects with darker, branched spines.

Damage. Adults and larvae feed on the underside of leaves and eat the softer leaf tissues. Damaged leaves appear netlike. Mexican bean beetles attack soybeans throughout the season, but most damage occurs in August and September.

Picture of Mexican Bean Beetle

Bean leaf beetle (Cerotoma trifurcata)

Yellowish-buff to reddish beetles which usually have black margins and four distinct black spots on the back. Spots are sometimes missing, but this insect always has a "V" mark at the front of the wing covers.

Damage. Beetles eat small rounded holes in the leaves. Unexpanded leaves are favored, and damage is often more alarming than serious since holes expand with leaf growth. Beetles frequently skin pods in late season and scar the developing seed within. Bean leaf beetles attack the plant throughout the season but are most severe in late July and early September in late-maturing beans.

Picture of Bean Leaf Beetle

Spotted cucumber beetle (Diabrotica undecimpunctata howardi)

Yellowish-green beetle with 12 black spots on the wing covers.

Damage. The cucumber beetle eats foliage but is seldom abundant enough to cause yield loss. Damage by this insect may be significant if many other defoliating pests are present.

Picture of Spotted Cucumber Beetle

Blister beetles (Epicauta pestifera, Epicauta lemniscata)

The margined blister beetle is black with gray margins on the wings. The threestriped blister beetle is yellow or orange with dark stripes running the length of the body.

Damage. Blister beetles eat foliage. Severe defoliation sometimes occurs on field margins. These insects tend to congregate and damage is confined to small spots.

Picture of Blister Beetle

Japanese beetle (Popillia japonica)

Shiny green or greenish-bronze beetles with reddish-brown wing covers. White tufts of hair are present on the sides and tip of the abdomen.

Damage. Japanese beetles eat the leaf areas between the veins and cause skeletonizing of the leaves. Although this insect is frequently found in soybeans during June and July, it seldom causes yield loss since defoliation is usually light and plants recover from damage before blooming.

Picture of Japanese Beetle

Pod Feeders

Insects which attack the fruit are the major reason for treating soybeans with insecticides. The corn earworm and stinkbugs are the major pod feeders although bean leaf beetle sometimes attacks pods. Not all soybean fields are subject to attack by pod feeders; corn earworm and stinkbugs both show varietal and planting date preferences. Corn earworm is mainly attracted to late blooming soybeans and scouting for this pest should begin as the July-August moth flight occurs. Additional information about insect activity and scouting is available through the county agricultural agent.

Corn earworm (Heliothis zea)

Small corn earworms are usually brownish with small dark spots. Larger caterpillars may be green, brown, yellow, or black. The bodies are stocky with prominent pale brown or orange heads. Light and dark stripes run the length of the body, which also bears five pairs of prolegs. When disturbed, this insect will drop to the ground and curl up. It does not crawl with a "looping" motion.

Damage. Eggs are laid on blooming or succulent soybeans. Blooming, open- canopy fields are highly preferred. Small earworms may be found in flower clusters. Feeding is usually first on foliage and later on pods. Severe pod damage and defoliation may occur.

Picture of Corn Earworm

Green stink bugs (Acrosternum hilare, Nezara viridula)

Adults are green, shield-shaped bugs. They fly readily and produce a distinct buzz when flying. Stink bugs give off a foul odor. Young bugs do not have wing covers and are green with black, orange and white markings.

Damage. Stink bugs suck the juices from immature soybean seeds and cause pod drop, yield loss, and quality decrease. These insects also spread yeast spot disease of the bean. Yield loss can be substantial.

Picture of Green Stink Bugs

Brown stink bug (Euschistus servus)

Shield-shaped bugs similar in appearance to the green stink bugs but dull brown and somewhat smaller. Younger bugs closely resemble adults but have no wings and are smaller.

Damage. This stink bug produces damage similar to the green stink bugs (see above).

Picture of Brown Stink Bugs

Stem Feeders

Loss from stem feeding insects is relatively minor. In dry years and/or in sandy soil conditions, lesser corn stalk borer can be a serious pest. The soybean stem borer is a new insect pest and may become more widespread; farmers usually detect this insect at harvest when plants are found to be cut-off and lodged. Other stem feeders regularly occur but are infrequently of economic importance.

Threecornered alfalfa hopper (Spissistilus festinus)

Adults are green triangular-shaped insects which are blunt in front and pointed at the rear. Young are similar to adults but are brownish, have no wings, and have numerous spines over the back.

Damage. Young soybean plant stems are fed upon near the soil. Feeding punctures girdle the stem, and plants frequently lodge during cultivation or windy periods. Lodging may result long after the damage occurred and is usually not yield reducing.

Picture of Threecornered Alfalfa Hopper

Soybean stem borer (Dectes texanus texanus)

Adults are charcoal gray beetles with very long antennae. Commonly found in the crown of ragweed during July and early August. Larvae are cream-colored, legless grubs which tunnel the stems of soybeans, ragweeds, and other plants.

Damage. The larva is the damaging stage. Infested soybean plants are tunneled and cut off at the base. Cutting off occurs after the plants have matured. Plants lodge and cannot be harvested. Early maturing and nonrotated soybeans are usually more seriously damaged.

Picture of Soybean Stem Borer

Grape colaspis (Colaspis brunnea)

Adults are tan beetles with darker lines running along the wing covers. They readily drop to the ground when disturbed. Larvae are small, brown-headed, white grubs which live in the soil. They are curved and somewhat flattened from top to bottom.

Damage. The main damage is done by larvae eating small roots and soft outer layers from below ground stems. Damaged plants are severely stunted. Damage is usually limited to soybeans following soybeans. Adults eat foliage but seldom occur in damaging number.

Picture of Grape Colaspis

Lesser cornstalk borer (Elasmopalpus lignosellus)

Yellowish-green caterpillars with reddish-brown cross bands. They are found at the soil surface in silk and soil tubes next to the plant. Larvae of this insect wiggle violently when disturbed.

Damage. Caterpillars tunnel or girdle small soybean plants at the ground level. Some plants may die, whereas others are severely stunted and may lodge. Damage is most common in late-planted soybeans on dry, sandy soils. This insect can be a serious pest of soybean.

Picture of Lesser Cornstalk Borer

Other Foliage Feeders

  1. Grasshoppers (Melanoplus spp.) Picture

  2. Saltmarsh caterpillar (Estigmene acrea) Picture

  3. Yellowstriped armyworm (Spodoptera ornithogalli) Picture

  4. Silverspotted skipper (Epargyreus clarus) Picture

  5. Soybean thrips (Sericothrips variabilis) Picture

Recommendations for insecticides that are effective in managing insect problems in soybeans can be obtained from the local Extension agent or the North Carolina Agricultural Chemical Manual, also available from the county Extension office.