Chinch bugs are not a new pest in sorghum, but for reasons that are not well understood yet, they have been an issue for some Kansas and Oklahoma growers the last few years—especially the last two years. The area of concern is primarily south central Kansas and northwest Oklahoma.

Lifecycle and Migration. Chinch bugs feed on a wide range of grass species but primarily become a problem in sorghum when they overwinter in wheat. The first generation of chinch bugs begin developing in wheat in the spring. Once the wheat dries down for harvest, the
chinch bugs migrate to nearby recently planted sorghum. Usually the infestation level is confined to the edge of the sorghum field closest to the wheat; however, many growers have reported their entire fields being infested. This is particularly true in double cropped sorghum planted soon after wheat harvest.

Damage and Symptoms. Chinch bugs damage sorghum by sucking juices at the root zone just below the soil surface or behind the leaf sheath. In addition, they secrete digestive enzymes that damage the surrounding tissue. This damage then opens up the tissue to diseases and other insects. Symptoms of injury will include yellow leaves and leaf sheaths and potentially stunted and wilted plants. Symptoms will be more pronounced under drought stressed conditions. Small plants can be completely killed requiring replanting.

Preventative Measures. The first line of defense is to plant insecticide-treated seed. Gaucho® (imidacloprid), Poncho® (clothianidin) and Cruiser® (thiamethoxam) are all effective seed treatments that should provide three weeks of control. In a few situations, the chinch bug population may overwhelm the seed treatment and still be a problem, but seed treatments should help.

Treatment Recommendations. Treatment thresholds will vary with plant size, but the most common recommendation for seedlings less than six inches is two or more chinch bugs on 20% of the plants. In addition to the leaf blade, look under the leaf sheath to find chinch bugs and on and just below the soil surface. These populations may eventually crash, or, in some cases, persist and produce a second generation that reaches an infestation level high enough to affect the sorghum later in the season. At this time we do not have a reliable threshold for chinch bugs on more mature sorghum.

Ongoing Research. The United Sorghum Checkoff Program is sponsoring trials with Kansas State University scientists to screen hybrids and lines for chinch bug tolerance as well as screening insecticides for their effectiveness on this pest. These results will be passed on to growers as soon as they are available.

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This story originally appeared in the Summer 2024 Issue of Sorghum Grower magazine.