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Cooperative Extension Service |
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Agricultural
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Aquaculture
Dale Bumpers College
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Insect Management
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Blister Beetles - The margined blister beetle and the striped blister beetle are both common in Arkansas. The adults are elongate with a broad head, narrow neck and long, slender legs. The margined blister beetle is dark gray to black, while the striped blister beetle is yellowish orange with brown stripes on the wing covers. Adults usually feed in groups in the field and can virtually strip all the leaves in spots in a soybean field. If enough areas in a field are spot treatment may be required.
Grasshoppers - The redlegged grasshopper and the differential grasshopper are two grasshopper species that are common in soybeans in Arkansas. Grasshoppers are rarely a problem. However, when grasshopper populations build to damaging levels, it usually occurs in fields with undisturbed pastures or hay fields close by. Typically they are found first along the edge of the field in large numbers early in the season and then disperse throughout the field as the season develops. Often treatments can be made along the field edge to control grasshoppers before they disperse if necessary. Grasshoppers will feed on leaves and pods, if they are available. Grasshoppers are favored by drought conditions and are often associated with two or more consecutive years of drought conditions.
Thrips - Thrips are one of the most abundant arthropods found in
soybeans. They are very small, less than one-tenth of an inch in length. The
most common species found in soybeans is the soybean thrips. Adults of this
species have characteristic transverse bands of brown and white on the abdomen.
Larval stages are yellow to orange in color. Thrips injury is characterized by a
silvery appearance to the leaves, blackening of the terminal and a general
reduction of plant vigor. Plants are most susceptible to thrips injury during
drought conditions or other stress situations that result in stunted growth.
Usually thrips are not a problem. However, when they occur in large numbers
(especially under stressful conditions), seedling mortality can occur. In these
situations, control measures may be necessary. Under normal conditions, plants
outgrow any injury and can withstand very high thrips populations (even up to
100 per plant).
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University of Arkansas • Division of Agriculture |
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Green
Cloverworm - The green cloverworm larva is light green in color with white
stripes running down each side of the body. A full-size larva is approximately
one inch in length. Green cloverworms can be distinguished from all other
lepidopterous larvae because they are the only ones that have three pairs of
abdominal prolegs. When disturbed, larvae wiggle violently and fall to the
ground, similar to the velvetbean caterpillar. The green cloverworm is usually
the first foliage-feeding lepidopteran found in soybeans. Although it is
considered an important pest in northern states, it rarely reaches damaging
levels in Arkansas. Many entomologists feel the green cloverworm may be more
beneficial than harmful because it provides a feeding source for beneficial
insects, allowing them to build up for the time when more damaging larvae may
occur. When the green cloverworm does reach damaging levels, it can be
controlled with the lowest labeled rates of insecticides. Commercial
formulations of Bacillus thuringiensis (Bt.) are very effective for control,
even at the lowest labeled rates.
Loopers
- The soybean looper and the cabbage looper are both commonly found in Arkansas.
Although the two species are almost indistinguishable, particularly in the
larval stage, control methods are extremely different. The cabbage looper is not
hard to control while the soybean looper is resistant to pyrethroids and
requires the use of more expensive insecticides to control.
Bean
Leaf Beetle - The bean leaf beetle is a small beetle which primarily feeds
on leaves but will occasionally feed on pods. Adults are about one-fourth inch
long with color ranging from light yellow to red with four black spots on their
back and a black margin around the edge of the wing covers. Also, a black
triangle will be present just behind the prothorax or "neck." This triangle is
always present, but the four black spots may or may not be seen. The grub or
immature stage is found in the soil where it feeds on roots and nodules. It is
white with a black head and anal shield. Damage by bean leaf beetle adult is
characterized by small circular holes between leaf veins as opposed to jagged
leaf damage from caterpillars and grasshoppers.
Velvetbean
Caterpillar - The velvetbean caterpillar is usually not a problem in
Arkansas. However, every five to ten years this pest is found in damaging
levels, usually only in the southern region of the state. The velvetbean
caterpillar is a voracious feeder and can strip a soybean field of leaves in a
short time.
Armyworms
- Several species of armyworms may be found in soybeans during the growing
season including the yellowstriped armyworm, the fall armyworm and the beet
armyworm. The yellowstriped armyworm occasionally occurs on seedling
soybeans in large enough numbers to cause damage, but usually the plants
can recover with no loss to yield potential, and control is seldom necessary.
The yellowstriped armyworm larva is dark to black with a yellow stripe running
down each side of the body. Also, there is usually a black spot on each side of
the first abdominal segment. As with the fall armyworm and beet armyworm, the
yellowstriped armyworm has four pairs of prolegs. 
Usually
fall armyworm populations occur late in the season and do not build up to
damaging levels. However, the fall armyworm has occasionally infested, been
observed to be present in the early spring on seedling soybeans at levels high
enough to cause damage. Control is usually not required. The fall armyworm
larvae can vary from tan to green in color and have black bumps with dark black
hairs on the body. On the eighth abdominal segment there are four distinct black
spots on the upper half of the body. Also, the fall armyworm has an inverted "Y"
on front of the head.
In
recent years the beet armyworm has been observed to develop large populations
late in the season. Larvae feed on blooms, pods and foliage and have caused
significant yield loss in isolated incidents. Mature larvae are green in color
with prominent lateral stripes. Unlike the fall armyworm, the beet armyworm has
no stout black hairs on the body, and there is usually a black spot on each side
of the body on the second thoracic segment, just above the middle pair of true
legs. The beet armyworm and fall armyworm have shown resistance to pyrethroids
and can be difficult to control.