Kansas State University

–by Dr. Jeff Whitworth

Most soybeans in north central Kansas, even double cropped fields, are getting to the stage where the pods are hardened enough to protect the beans inside (see picture of pod feeding scar by bean leaf beetles and an adult bean leaf beetle (pic1). Woollybear caterpillars (pic 2) are becoming more noticeable as the soybean leaves start to senesce, the caterpillars are getting larger and thus more visible, and as they move to the ground, looking for overwintering sites.

–by Dr. Jeff Whitworth

Most soybeans around north central Kansas are now well into the mid to late reproductive stages. There doesn’t seem to be much potential for any massive infestations by defoliators and even if there was, as the soybeans get farther along in their development the leaf tissue becomes less needed. However, the direct pests, those that feed on the marketable product, are still very active and some are even increasing. Bean leaf beetle adults are active, feeding on pods, however, there do not seem to be as many as in past years. Soybean podworms, i.e., corn earworms/sorghum headworms, are very common and seem to be increasing in numbers in some areas. Treatment thresholds are usually considered to be 1 larva/row foot, with small worms, i.e., less than ½ inch (see pic1) and they are feeding on the seeds (beans). These larvae feed for roughly 2 weeks before pupating. As the larvae develop larger than the one shown here (see pic 1) they consume more as they get bigger and this feeding will continue for about another 7-10 days at these temperatures

–by Dr. Jeff Whitworth

Soybean aphids continue to migrate into the state and with the predicted cooler temperatures may be able to successfully colonize. Thus, monitoring should continue until /or if hotter temperatures return.

–by Dr. Jeff Whitworth

Defoliators are still present in most soybean fields throughout north central and south central Kansas, especially in double cropped fields. However, infestation levels are still relatively low and growing conditions still seem to be really good.

Podworms (corn earworms/sorghum headworms) are just starting to move into soybeans from sorghum as the sorghum gets past the soft dough stage. Thus, as the soybeans are in the reproductive stages, with new succulent pods being added to the plants, these larvae, plus adult bean leaf beetles and possibly stink bugs, may start feeding on them, which can impact yield pretty quickly. Therefore, using a drop cloth and vigorously shaking the plants over it to count the bugs that fall on it is highly recommended to quantify the pests present, which is necessary to determine management options.

Also, the results of Dectes stem borer tunneling is becoming visible as scattered petioles start to die. Most of the larvae sampled were still relatively small (see pic), i.e., probably only 1/4 – 1/3 grown.

Dectes stem borer

–by Dr. Jeff Whitworth

The usual soybean defoliators, i.e., thistle caterpillars, garden webworms, green cloverworms, etc. have just started feeding again as small larvae. However, soybeans should have enough foliage, and the growing conditions are good enough, that this feeding should be negligible. Please note, Ms. Rene Hessel, a soybean researcher for KSU, and a soybean aphid detector extraordinaire, reported finding the first soybean aphids in Riley Co. on 7 August (see pic). Soybean aphids have migrated into Kansas every year since 2002, however, there has only been a couple years in that time that conditions were conducive enough to allow the aphid populations to build up to treatable levels. Most conventionally planted soybeans are in the early reproductive stages throughout south central and north central Kansas, so these aphids warrant periodic monitoring.

Also, just FYI. There seems to be a healthy number of stinkbugs (see pic) in most soybean fields at the present time. Remember, when pods are filling, the beans are vulnerable to both “podworms” and these stinkbugs.

Soybean aphid (photo by Rene Hessel)

Adult Green Stinkbug

–by Dr. Jeff Whitworth and Dr. Holly Davis

Soybeans appear to be relatively pest free at the present time – but looks can be deceiving.  There are a few small green cloverworms, thistle caterpillars, soybean podworms (corn earworms) and webworms, along with stink bugs and spider mites.

These pests are probably only going to increase in the next few weeks.  Bean leaf beetle adults will also likely be emerging and showing up in fields soon.  As the beans continue to develop so will the pests, thus monitoring should continue until beans senesce.

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Japanese beetle adults have also been emerging over the past week or two.  These adults will feed on just about any pollen, nectar, or succulent plant source for a few days then disperse to begin ovipositing into the soil.  The adults may attack emerging silks in corn or new succulent leaves in soybeans, but typically only around the edges of fields.