Kansas State University


Extension Entomology

Month: September 2017

Soybean Update – Thistle caterpillars, Stink bugs, and Soybean Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Thistle caterpillars have mostly vacated their webbed cells and are or have pupated.  That is why there are huge numbers of painted lady butterflies flying around on most rural roads throughout north central Kansas.  Hopefully, these butterflies will head south for overwintering and will not start laying eggs in soybean or sunflower fields.  However, fields need to continue to be monitored for small thistle caterpillars, especially double-cropped soybeans. Additionally, monitor for the continued presence of green cloverworms, although these populations seem to be declining quite rapidly around north central Kansas.


Phytophagous stink bugs, both brown and green, are increasing in many soybean fields.  Either may insert their mouthparts into the seed within the pods and suck out juice from the developing seed.  However, there are also brown stink bugs that are predatory on pests like the yellowstriped armyworm (shown below) which has been killed and is being utilized as a food source by this beneficial stink bug.


Soybean aphid populations are still present in all fields examined this week in north central Kansas, but are not increasing in density or coverage.



For management decisions for all soybean pests please see the 2017 Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf


Sorghum Update – Chinch Bugs, Sugarcane Aphids

–by Dr. Jeff Whitworth and Dr. Holly Schwarting

Chinch bug populations throughout north central and south central KS are not going away. These small sucking insects may still cause plant lodging, especially in these areas where moisture has been lacking



A small colony of sugarcane aphids was detected in Dickinson County on 30 Aug.  The colony was on the underside of one leaf on whorl-stage sorghum.  Tom Maxwell, Saline Co. Agricultural Extension Agent reported finding sugarcane aphids in Saline, Seward, and Ottawa Counties, also on 30 Aug. To see the current 2017 Sugarcane aphid distribution map, please visit MyFields: https://www.myfields.info/pests/sugarcane-aphid

For monitoring and management considerations for sugarcane aphids, please refer to the Sugarcane Scout Card: https://www.myfields.info/sites/default/files/page/ScoutCard%20KSU%20v05312017.pdf

Or see the 2017 Sorghum Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF742.pdf




Soybean Update – Defoliators, Pod and Bean Feeders

–by Dr. Jeff Whitworth and Dr. Holly Schwarting


Soybeans continue to be the focus of attention of many defoliators, as well as bean and pod feeders, throughout north central Kansas. Thistle caterpillar populations seem to be largely late instar larvae and/or pupating inside of their very characteristic chrysalis.  Green cloverworms also seem to be increasing in both size and densities.  These are the main two species feeding on the leaves, but throw in a few yellowstriped armyworms and blister beetles and they all add up to a formidable group of very active defoliators.  Fortunately, soybeans are very resilient at coping with the loss of leaf tissue.  However, periodic monitoring should be continued, and if considering insecticide applications, please consult the 2017 KSU Soybean Insect Management Guide for treatment thresholds and insecticides labeled for these pests.



Pod and bean feeders seem to be just getting started. Bean leaf beetle adults may feed on the pods and will continue to do so until pods dry.  Soybean podworms (aka corn earworms) may feed upon the bean within the pod and thus both may reduce yields relatively quickly.  Fortunately, podworms will only feed on the beans for about two weeks.  However, bean leaf beetle adults may feed on the pods as long as they remain green.  Stink bug populations are also increasing and these may also feed directly on the developing beans within the pods.  Again, for management decisions, please refer to the 2017 KSU Soybean Insect Management Guide: https://www.bookstore.ksre.ksu.edu/pubs/MF743.pdf