<< BACK
Soybean Insects

Bean Leaf Beetles
Bean Leaf Beetles winter under plant debris and move into soybean fields just after emergence. The adults begin feeding on cotyledons and leaflets until early July, lay eggs in the soil and die. The larvae hatch and feed on soybean nodules which is not thought to cause any economic losses. Pupation occurs in the soil and the second generation of beetles emerge to feed on leaves and developing pods. Begin scouting for bean leaf beetles at emergence, if beetles damage cotyledons before leaves emerge, stands can be severely reduced. Later, soybeans with 4 or fewer nodes on the main stem and fully developed leaves will tolerate leaf feeding by up to 7 beetles per row foot and up to 25% defoliation.

The second generation beetle is usually of most concern, begin scouting during the R4 pod development state and continue to R7 yellow pod stage. Most university extension offices have economic threshold calculators for figuring if spraying is beneficial. Generally, it will take 50 beetles per row foot to cause enough defoliation to reduce yields. However, if enough pod feeding occurs to damage 2 to 3 seeds per plant, insecticide treatment may be justified. Always scout at least 100 feet from the field edge and look for other insect pests, such as grasshoppers, when scouting for bean leaf beetles. Unmonitored Bean Leaf Beetles can be one of the most destructive insect pests to soybeans. Proper scouting techniques and planting soybeans at the end of their optimum planting date for maximum yield can reduce the risk of losses by Bean Leaf Beetles.

Spider Mites
Spider mites are tiny animals more closely related to chiggers, ticks or spiders than to insects. Fertilized females overwinter in various grass, legume fields, and ditches then move into fields in the spring. The two-spotted spider mite causes the most problems on soybeans and corn in the Midwest. Spider mites have five stages including the egg stage, 6- and 8-legged immature stages, and 8- legged adult stage. Females mate and start laying eggs 1 to 2 days after becoming an adult. They can lay 10 eggs per day for up to 30 days. Normally, 12 to 14 days are required from egg laying to adult transformation, but during hot and dry spells, this time can be reduced to 5 days. Therefore, mite populations and concerns for proper mite scouting increase during hot and dry periods.

Mites live in webbed colonies on lower side of leaf surfaces. Spider mites feed by piercing individual leaf cells and sucking out the contents. The leaf loses its photosynthetic ability and initially yellow dots appear on leaf surfaces, then leaves turn yellow, turn brown and die. Mites can be difficult to see and symptoms can often be confused with herbicide injury or foliar diseases. When scouting for mites take along a white piece of paper to tap on the underside of symptomatic leaves and a l0x lens to detect yellowing and live mites. As the food source is depleted, mites climb to the top of the plant and sail down wind to a new host. Therefore, new mite populations will grow downwind. Mites can be a serious problem and can reduce yields sometimes up to 60% or more in infested areas. Scout carefully and rescout treated fields or areas, especially during hot and dry weather where spot treating may not work because of large unseen infested areas elsewhere in the field.

Other Insects

When scouting for these insects look for other insect problems like grasshoppers, green cloverworms, yellow wollybear, soybean looper, and others that may cause yield losses. Scouting can help reduce yield losses from insect damage and provides producers with the ability to react in a timely manner when insecticide treatments are warranted.

BACK TO TOP