Soybean South

 - INSECT CONTROL -

Bad Bugs Of Summer

Stink bugs, soybean loopers and, in the last couple of years, corn earworm
have been the main insect pests that attack soybeans
in the Mid-South.

By Angus Catchot

Each year, producers in the Mid-South face a variety of insect pests in soybeans. Depending on the year, the key pest may change drastically. For instance, as cotton acres have declined over the last several years, producers are planting more grain crops, which requires manipulation of planting dates and maturity groups to spread the harvest around other crops such as corn.

As a result, a larger portion of the crop is exposed to the late-season buildup of pests, such as soybean loopers and stink bugs, attacking soybeans. Soybean loopers are migratory pests that move north every year from southern latitudes to attack soybeans. Soybean loopers reduce yield by feeding on the foliage of the plants, which is important for photosynthesis during pod filling. Traditionally, many producers have missed the late-season migration of soybean loopers by planting group IV varieties in early April, which mature prior to soybean loopers arriving.

Soybean loopers can be particularly troublesome since they are resistant to a number of insecticides commonly used to control other pests. Often, late in the season when soybean loopers are present in soybeans, there are other pests that require treatment at the same time. Because of insecticide resistance issues with soybean loopers, producers are often required to tankmix insecticides to control multiple pests, which increases the cost of treatment.

Stink bugs cause quality issues
Stink bugs also are a serious threat to Mid-South producers. Stink bugs are seed feeders by nature and prefer to “infest” soybeans when pods are filling seeds (R5-R6). Because stink bugs feed directly on the seed they can cause serious quality issues when not properly managed.

In the Mid-South, there are three common stink bug species that are frequently encountered in soybeans: The green stink bug, the Southern green stink bug and the brown stink bug. In recent years, another species, the redbanded stink bug, has become more common in the Mid-South. This species has proven to be more difficult to control, and preliminary research from Louisiana suggests that it is more damaging than other stink bug species attacking soybeans in the Mid-South. Researchers and Extension agents across the region are trying to educate producers and consultants about the threat of redbanded stink bugs.

Corn earworms on the rise
An occasional pest that has caused considerable concern among soybean producers in the Mid-South the last couple of years is the corn earworm. The higher number of fields reaching economic threshold for corn earworm is likely due to the increased corn acres across the Mid-South region. Corn is a highly attractive host for this pest, which can produce high numbers of corn earworm that can move into soybeans.

Soybeans that are flowering with open canopies are particularly attractive to the corn earworm moths. This pest feeds directly on the reproductive parts and can cause considerable damage if not caught in time. Corn earworms feed low in the canopy on blooms, small pods and seeds. Because of where they feed on the plant, it is often difficult to get sweep nets deep into the canopy for accurate counts when sampling.

When corn earworms are present, it is recommended to modify your sampling technique with sweep nets and drive the net deeper into the canopy, especially on tall beans. Drop cloths are also very good if soybeans are planted on wide rows. Entomologists across the Mid-South are working on a multi-state project to better refine the economic threshold for corn earworm in soybeans.

Pyrethroid insecticides have been the product of choice to control this pest because of the price and efficacy. However, in recent years, there has been concern that tolerance levels are increasing in the corn earworm in some areas of the South. Researchers are actively monitoring pyrethroid resistance levels across the South for this pest to educate producers should problems occur.

Contact Angus Catchot, Mississippi State Extension entomologist at acatchot@ext.msstate.edu.