Occasional & Non-Economic Soybean Pests

Alfalfa caterpillar

Colias eurytheme Boisduval

Appearance and Life History

Alfalfa Caterpillar Alfalfa Caterpillar
Photo by J. Obermeyer

This caterpillar, which is up to 1-1/2 inches (38 mm) long, has a smooth lime-green body with a white stripe on each of its sides. Within each white stripe is a thin red line.

Damage

Though this caterpillar is most commonly found in alfalfa, it can occasionally be found defoliating soybean leaves.

Sampling Method

Sampling for this occasional soybean invader should not be necessary.

Management Guidelines

Consider their damage additive with other defoliators and refer to the "Green Cloverworm" management guidelines.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Alfalfa weevil

Several species

Appearance and Life History

Alfalfa Weevil Alfalfa Weevil
Photo by J. Obermeyer

Several weevils/beetles that may feed on alfalfa will occasionally damage soybean. Alfalfa weevil, clover leaf weevil, and clover root curculio have been observed feeding on soybean seedlings. Further descriptions and life cycle information for these pests can be found in the alfalfa section.

Alfalfa Weevil damage Alfalfa Weevil damage
Photo by J. Obermeyer

Damage

When alfalfa is tilled and destroyed in the spring and followed with soybean, these insect pests may feed-on and damage soybean as the seedlings emerge. This complex of weevils/beetles may defoliate unifoliolate and early trifoliolate leaves, but more importantly they may feed on the stems of the soybean, causing plant death.

Sampling Method

Sampling is recommended if plants, following spring-tilled alfalfa, are being damaged by any of these species. After positively identifying the pest(s), determine the severity of damage and the threat to the soybean stand.

Management Guidelines

If the soybean stand is being economically reduced, the weevil/beetle population should be controlled. Replanting may be necessary if the stand has been reduced to critical levels. If a control is not applied, but replanting occurs, watch emerging seedlings for weevil/beetle feeding activity and apply a control if a critical number of plants are threatened.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Blister beetles

Epicauta spp.

Appearance and Life History

Gray blister beetle Gray blister beetle
Photo by University of Illinois
Black blister beetle Black blister beetle
Photo by J. Obermeyer
Margined blister beetle Margined blister beetle
Photo by B. Christine
Striped blister beetle Striped blister beetle
Photo by J. Obermeyer

There are several species of blister beetles that may be found in soybean. These include the margined, black, striped, and gray blister beetles. They all have relatively soft wing covers and are about 1/2 to 3/4 inch (13 to 19 mm) long. Eggs are laid in the soil and the larvae, which remain in the ground.

Damage

These beetles, which are often found clumped in areas of a field, primarily feed on soybean foliage late in the season.

Sampling Method

Their defoliation should be considered the same as other foliage feeders that may be present at the same time. Caution should be used when sampling an area infested with these beetles. If squeezed, they exude an oil (cantharidin) that may cause blisters on the skin.

Management Guidelines

Should damage become apparent in areas or whole fields, treatment may be necessary. Refer to the defoliation guide for "Mexican Bean Beetle" in soybean to determine if control is necessary.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


European Corn Borer

Ostrinia nubilalis Hübner

Appearance and Life History

Mature larva in silk tunnel Mature larva in silk tunnel
Photo by J. Obermeyer

The mature European corn borer larva is about 1 inch (25 mm) long, creamy to grayish with rather inconspicuous rows of small, round, brown spots running the length of its body. A complete description of the corn borer and its development can be found in the corn section.

Stalk entry hole and frass Stalk entry hole and frass
Photo by B. Christine

Damage

Though it is usually a pest of corn, soybean is one of many hosts of European corn borer. Larvae bore into soybean stems causing leaf wilting and premature death of plants. Corn borer frass can be seen at stem entrance holes.

Sampling Method

Routine sampling for this occasional invader of soybean should not be necessary. However, if damage is noted in a field it should be evaluated.

Management Guidelines

If first generation borers cause serious enough damage to threaten yields, replanting may be necessary (refer to "Cutworms" in the soybean section). For late season damage, no management strategies are available.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Grape Colaspis

Colaspis brunnea Fabricius

Grub Grub
Photo by J. Obermeyer
Adult Adult
Photo by J. Obermeyer

Appearance and Life History

The adult is a yellowish-brown, elliptical beetle about 3/16 inch (4.7 mm) long with wing covers that are marked with longitudinal rows of ridges. The tiny (1/8 inch or 3 mm long), white grub is comma-shaped with a brown head. The white pupa may be found a few inches deep in the soil near damaged plants. There is one generation per year. It overwinters as a grub in the soil and emerges as an adult in late June to early July. Adults proceed to feed, mate, and lay eggs which hatch in early fall.

Grape Colaspis damage Grape Colaspis damage
Photo by J. Obermeyer

Damage

The grubs are root feeders and may cause wilting and stunting of plants. Under a heavy infestation, small plants may die. Damage is usually noted in patches within a field. Damage is most likely to occur following clover or alfalfa, and occasionally where patches of smartweed existed the previous year.

Sampling Method

Dig up plants in 2 linear feet (0.6 m) of row in damaged areas of the field. Inspect for missing and/or damaged roots. Carefully sort through the soil and verify the presence of grape colaspis grubs and/or pupae.

Management Guidelines

There is no known economic threshold or rescue treatment for grape colaspis. If necessary, replanting should be done after grubs have begun to pupate (refer to "Cutworms" in the soybean section for replanting information).

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Loopers

Several species

Appearance and Life History

Looper Looper
Photo by J. Obermeyer

Loopers, which are light green with thin white stripes and up to 1-1/2 inches (38 mm) long, are often mistaken for green cloverworm. Loopers have three abdominal prolegs in contrast to four for the green cloverworm, and they walk in a looping motion., as shown in the photo at right.

Damage

They are general defoliators, causing damage much like the green cloverworm.

Sampling Method

Since this occasional pest is often present with the green cloverworm and its damage is similar, separate sampling for these species should not be necessary.

Management Guidelines

Refer to the "Green Cloverworm" management guidelines in this section.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Rootworm beetles

Diabrotica spp.

Appearance and Life History

Male and Female western corn rootworms Male and Female western corn rootworms
Photo by L. Bledsoe
Northern corn rootworm Northern corn rootworm
Photo by B. Christine
Southern corn rootworm Southern corn rootworm
Photo by J. Obermeyer

There are several species of rootworm beetles that may be found in soybean. These include the western, northern, and southern corn rootworms. Both the western and northern species are considered major pests of corn, whereas the southern species (also known as the spotted cucumber beetle) is more of a pest in cucurbit and melon crops. Complete descriptions and life cycle information for these beetles can be found in the corn section.

Damage

These beetles will occasionally feed on soybean foliage, flowers, and pod buds. Their foliage feeding looks similar to Japanese beetle damage, skeletonized leaves with larger leaf veins left intact.

Sampling Method

Sampling for these beetles should not be necessary since they don't normally threaten soybean yields. Consideration of damage to corn roots following soybean should be considered when high numbers of rootworm beetles are found in soybean fields (refer to "Corn Rootworms" in the corn section for information on rootworm beetles in soybean and subsequent damage in corn).

Management Guidelines

The damage caused by the feeding of these beetles on soybean foliage is believed to be of little economic importance. Concern should be for next year's corn when abundant western and/or northern corn rootworm beetles are present during egg laying.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Silver-spotted skipper

Epargyreus clarus Cramer

Appearance and Life History

Larva Larva
Photo by B. Christine

These odd looking caterpillars, which are up to 2 inches (50 mm) in length, have brownish-red heads with two orange spots and a yellowish-green body. Larvae can often be found in leaves that have been rolled together and held by the caterpillars' silken threads. Adult skippers, which are commonly seen feeding on flowers late in the summer, have an obvious silver-white splotch on each wing.

Adult Adult
Photo by J. Obermeyer

Damage

Larvae feed on leguminous plant foliage. Their damage is generally of minor importance.

Sampling Method

Because this occasional pest is often present with other defoliators, separate sampling should not be necessary.

Management Guidelines

Refer to the "Green Cloverworm" management guidelines.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Whiteflies

Several species

Appearance and Life History

Whitefly, greatly magnified, on underside of leaf Whitefly, greatly magnified, on underside of leaf
Photo by J. Obermeyer

The adult, which is about 1/16 inch (1.6 mm) long, has white powdery wings. The whitish, scale-like nymphs are smaller than the adults and somewhat oval in shape. Eggs, nymphs, and adults can be found inhabiting the underside of leaves.

Damage

Both adults and nymphs suck plant juices causing yellow speckling of leaves. Unless whitefly populations are extremely high and soybean is under drought conditions, whitefly damage is not likely to be economic.

Sampling Method

Sampling is not necessary for this insect. "Kicking-up" whiteflies while walking through fields late in the season is not uncommon, nor is it reason for concern.

Management Guidelines

Since economic damage is highly unlikely, no management guidelines have been established for whiteflies.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.


Wooly bear caterpillars

Several species

Appearance and Life History

Adult Adult
Photo by J. Obermeyer

The adults, known as tiger moths, can commonly be seen in the spring and mid summer at night near bright lights. These moths, with a 1-1/2 to 2 inch (38 to 50 mm) wing span, have snow-white, yellowish, or white and black-spotted wings with abdomens that are white to yellow. White to yellow spherical eggs are laid in clusters on leaves. The white, yellow or brown "woolly" or furry caterpillars range in length from 1/4 to 2 inches (6 to 50 mm). Mature larvae leave the plant, seek a protected place, and pupate inside a thin silken cocoon which is covered with the hairs from their bodies. There are two generations per year, with only the second or mid season larval population posing a potential economic threat to soybean.

Woollybear caterpillar young larvae feeding Woollybear caterpillar young larvae feeding
Photo by J. Obermeyer

Damage

Woolly bear caterpillars are foliage feeders. Generally, their presence and damage is not noticed until late in the season.

Sampling Method

Determine defoliation levels in each of 5 areas of the field. Inspect the larvae for a commonly occurring fungal disease. If infected, they will appear "frozen" and may appear water soaked or covered with cottony-like substance.

Management Guidelines

Soybean Insect Control Recommendations: E-series 77-W (PDF)

Should damage become apparent in areas or whole fields, treatment may be necessary if 25% or more defoliation is noted during pod fill stages. Before treating, however, look for diseased larvae. When larval numbers reach high levels, naturally occurring fungal pathogens often control the woolly bear population.

If control is necessary, contact your state Cooperative Extension Service or click here for control materials and rates.