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Insect Management
Soybean Insect Management
Pod Feeders

The pod feeders represent the insects that have the greatest potential for causing economic losses to soybeans. The soybean plant does not have the ability to compensate for damage at this stage of growth, and injury to pods and/or seed is directly reflected in lower yields.

Management Tip: Scout fields closely at least once a week starting at bloom and examine the plants for visual signs of damage.

While small larvae feed on new, tender leaves and blooms, larger larvae can be found on any part of the plant and will feed on leaves, stems or pods but prefer blooms. Small larvae are off-white in color, but larger larvae can vary in color from yellowish-green to green, pink, brown or even black, each having longitudinal light-colored lines along the body. Compared to armyworms, they generally have much more hair over the body. The head is most often orange in color. When disturbed, these larvae usually curl up into a "C' shape. Larvae, particularly small ones, are subject to high mortality from natural enemies. For this reason, pesticide treatment recommendations are generally aimed at medium and large larvae.

The most vulnerable time for soybean fields to infestation by the corn earworm is during bloom (R2 growth stage), which usually coincides with the second field generation. Fields should be closely monitored at this time, particularly fields that are blooming and have not achieved canopy closure. Also, the treatment level for corn earworm is reduced for drought-stressed beans because the ability of plants to compensate is reduced in this situation. Studies have shown that, under normal conditions, when larvae eat one bean out of a pod, the other beans in the pod will increase in size to overcome the loss.

The rates of insecticide needed for control are typically lower for soybeans than cotton because the larvae are much more exposed to the insecticide. The treatment level for corn earworm in soybeans prior to bloom is 40 percent defoliation. After bloom, treat when populations approach four larvae that are one-half inch or longer per row foot (38-inch rows). For dryland soybeans under stress, treat at three larvae per row foot. 

Stink Bugs - Three species of stink bugs are found in Arkansas. They are the green stink bug, the southern green stink bug and the brown stink bug. Both the adult and nymphal stages of the stink bug complex can cause injury to soybeans. Damage is caused when they insert their piercing-sucking mouthparts into the plant and extract plant juices. The stink bug will feed on the stems, foliage, pods and blooms. Damage is greatest when they feed on the seed in the developing pod. Stink bug feeding can cause abortion of blooms and pods resulting in yield reduction. Stink bug feeding early in the development of pods can result in shriveling of seed or seed size reduction. Feeding on large-sized seed results in seed discoloration and lowering of seed quality. When stink bugs feed on the developing seed, digestive juices are injected into the seed causing deterioration of tissue.

Stink bug eggs are distinctively laid on the leaves of soybeans in clusters in tight rows. Individual eggs are barrel-shaped. As nymphs, they are gregarious in habit and remain close to the egg mass from which they hatched. As they develop, they begin to feed and disperse. Southern green Stink bug nymphs are, at first, reddish black or black. Later they develop a white spot on the back. As they reach mid-size, they turn black in color or green with pink markings on the back and white spots on the abdomen. Late instar nymphs are lighter green than the adult stink bugs with pink and black markings and white spots on the margin of the abdomen. Southern green stink bug adults can be differentiated from green stink bug adults by the red bands on the antennae. Green stink bug nymphs are, at first, reddish brown, then light green with black and white stripes on the abdomen.

Late-stage nymphs are green and have stripes on the abdomen colored yellow and black or green with a black spot in the center of the abdomen. Adult green stink bugs have black bands on the antennae. Brown stink bug nymphs are light brown with brown spots down the middle of the abdomen. The brown stink bug adult is brown and has rounded shoulders. They are often confused with the spined soldier bug, a predaceous stink bug which has sharp points on each shoulder.

Stink bugs are often found along field borders, particularly along tree lines where they overwinter as adults. Threshold levels in Arkansas are one per row foot (38-inch rows) after blooming and pod formation begins. 

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Last Date Modified 07/15/2008
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