No. 12 Article 6/June 16, 2006

Some Dry-Environment Insect Problems--Grape Colaspis and False Chinch Bugs

When I receive reports of both grape colaspis injury (especially in soybean) and false chinch bugs, I am always reminded of 1988. Not that I am predicting a drought, but both of these insects caused significant problems early in the season in 1988, to be overshadowed later by twospotted spider mites. We have not received a large number of reports of these two insects causing problems, but the reports are worth mentioning nonetheless.

Let’s start with grape colaspis. In issue no. 10 (June 2, 2006) of the Bulletin, I wrote about grape colaspis larvae injuring corn. Since that article was published, a few more reports of such injury have trickled in, primarily from north-central Illinois. The symptoms reported were classic--stunted plants, purple stems, "burned" leaf edges, classic symptoms of phosphorous and potassium deficiencies. These symptoms arise from the colaspis larvae basically denuding the roots of root hairs.

Although grape colaspis and corn are most commonly associated, grape colaspis larvae also can injure soybean. Grape colaspis injury to soybean was relatively widespread in 1988 when soybean seedlings were struggling to grow in dry soils. Hundreds of fields were affected, with as much as 95% stand reduction in a few fields. However, it’s important to note that most of the affected soybean fields were soybean planted after PIK (payment-in-kind) acres on which legumes (e.g., clover, alfalfa) had been grown. We received few reports of grape colaspis damage in fields of soybean planted after corn. Nonetheless, it’s worth keeping grape colaspis larvae on the "culprits-to-consider" list.

On June 13, I had a telephone conversation with a grower in Macoupin County who suspects a grape colaspis problem in a field of soybean planted after red clover (almost a dead giveaway). Although I have not seen the insects firsthand, the description of the larvae and the situation have grape colaspis written all over them. Grape colaspis larvae chew tunnels and occasionally girdle soybean roots, resulting in plants that wilt and often die. As is the case with corn, rescue treatments are not effective. Replanting is the only solution, but the overall cost of replanting must be considered before making such a decision at this late date. Fortunately, grape colaspis larvae should finish feeding by mid- to late June, depending on the location, after which they will pupate and eventually emerge from the soil as beetles.

Now, let’s turn our attention to false chinch bugs. I always associate the phrase "The ground seemed to be moving" with false chinch bugs because their sheer numbers in a given field can be awe-inspiring. Robert Bellm, crop systems Extension educator in Edwardsville, visited an 80-acre soybean field in Jersey County on June 7 and discovered patches of injury caused by false chinch bugs. The soybeans had been planted no-till into cornstalks, and there had been a heavy infestation of shepherd’s purse and pennycress. The false chinch bugs seemed to be most prevalent in areas infested with shepherd’s purse. Conditions in the field were very dry.

Soybean seedlings injured by false chinch bugs (photo courtesy of Robert Bellm, University of Illinois Extension).

False chinch bug nymphs are ash-gray with brown-white mottling on the back and red mottling on the abdomen. Adults are 1/8 inch long, dirty gray, with brown or black markings. False chinch bugs prefer to feed on plants in the mustard and beet families, but they have been known to cause injury to both soybean and corn. Both the nymphs and adults use their piercing-sucking mouthparts to feed on plant fluids, and injured plants wilt and may die.

False chinch bug adult (photo courtesy of Robert Bellm, University of Illinois Extension).

So far as I know, there are no insecticides labeled for control of false chinch bugs, probably because these insects occur so infrequently. If anyone working for an insecticide manufacturer wishes to correct me, please contact me and I will share the information with our readers.--Kevin Steffey

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