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.
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.
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.
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.
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
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.
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
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.
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
Damage. Blister beetles eat foliage. Severe defoliation sometimes occurs
on field margins. These insects tend to congregate and damage is confined to
small spots.
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.
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.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.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.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.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.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.Spotted cucumber beetle (Diabrotica undecimpunctata howardi)
Yellowish-green beetle with 12 black spots on the wing covers.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.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. 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.
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.
Damage. This stink bug produces damage similar to the green stink bugs
(see above).
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.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.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. 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
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.
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.
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
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.
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.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.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.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.Other Foliage Feeders
