Scout Soybeans for Stink Bugs

Bill Cissel, Extension Agent – Integrated Pest Management; bcissel@udel.edu

Stink bugs are starting to show up in soybeans. We have three stink bug species that are considered a pest of soybeans. They include the green stink bug, brown stink bug, and the invasive brown marmorated stink bug (BMSB). All three species feed on soybean pods and seed using their piercing-sucking mouth parts. Feeding injury to soybeans in the early stages of pod development, R3 to R4 (beginning pod to full pod), can result in aborted pods or underdeveloped flat pods. Feeding injury to larger seed, between R5 and R6 (beginning seed to full seed) results in shriveled, deformed or even aborted pods.

Flat pod

Seed injury

Stink bug feeding injury has also been shown to cause delayed plant development, often referred to as “stay green syndrome”. In response to stink bug feeding, soybeans will delay development in an effort to produce more seed to compensate for what has been lost. As a result, the portions of the field with heavy stink bug infestations remain green while the remainder of the field dries down.

Stay green syndrome

Recognizing stink bug adults is fairly easy with just a little practice. The most common mistake is confusing the native brown stink bug with the invasive BMSB. The easiest way to distinguish between these two species is by looking at the antennae. If the antennae are striped black and white, you know that it’s a BMSB because that is the only species we have that has banded antennae. The other feature that can be used to distinguish between the two species is the color of the abdomen. Brown stink bugs have a yellow-green colored stomach compared to BMSB which have a cream or tan colored stomach. It’s important to be able to distinguish our native stink bug species (green and brown) from the invasive BMSB because they have different infestation habits which can change our management strategy. Research conducted in the Mid-Atlantic States has also determined that BMSB feeding injury on soybeans is slightly more damaging compared to our native species.

Identifying nymphs can be a little more challenging and the most common mistake is to misidentify stink bug nymphs as beetles because of their shape. Stink bugs nymphs also do not necessarily resemble the adults but looking at the mouth parts can be used to distinguish beetles, which have chewing mouth parts, from true bugs with piercing-sucking mouth parts. When scouting, it is important to count nymphs and adults because both life stages attack soybeans.

Green Stink Bug Adult

Green Stink Bug Nymph

Brown Stink Bug Adult

Brown Stink Bug Nymph

Brown Marmorated Stink Bug Adult

Brown Marmorated Stink Bug Nymph

The threshold for our native stink bug species in soybeans is 5 per 15 sweeps. The threshold for BMSB is 3-5 per 15 sweeps. In many fields, the complex of stink bug species will include a mix of BMSB, green, and brown stink bugs. When a mixture of species is present, the threshold is 5 per 15 sweeps. All thresholds should include the total number of adults and medium to large nymphs.

Sampling full season soybeans can be a challenge because the plants are usually tall and difficult to navigate. Stink bugs have a strong startle response and drop from the plant when disturbed. An alternative sampling method to sweep net sampling is performing a timed, 2 minute visual count. This is a preferred method to sweep net sampling because it is not only safer for the sampler (i.e. less likely to become entangled in soybean plants) but is also more accurate. The threshold that has been developed for BMSB in soybeans using the visual 2 minute count is 3-5 medium to large nymphs and adults.

Brown marmorated stink bugs differ from our native species in that they have a behavioral habit of only infesting the outer edges of soybean fields. This habit provides an opportunity to concentrate control efforts on the edges of soybean fields by performing an edge only treatment if BMSB is the only species present. Based on research conducted in the Mid-Atlantic, this approach has been found to be an effective management strategy to control BMSB in soybeans. Below is a graph showing a typical distribution of BMSB in soybeans. Based on the graph, the highest populations of BMSB are concentrated on the field edge, typically the first 30-50 ft into the field. However, be sure you are also sampling the interior portions of the field because our native stink bug species do not share this same infestation habit and are often distributed throughout the entire field.

Here is a link for more information discussing the Biology and Management of Brown Marmorated Stink Bugs in Mid-Atlantic Soybeans: https://pubs.ext.vt.edu/content/dam/pubs_ext_vt_edu/ENTO/ENTO-168/ENTO-168-pdf.pdf

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