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Issue No. 8, Article 3/May 18, 2007

Black Cutworm Damage Is Economic In a Number of Fields in Illinois

We have received numerous reports of economic damage (i.e., significant plant cutting and stand reduction) caused by black cutworms this spring. Most of the activity thus far has been in western Illinois, but economic infestations have occurred in some fields in southwestern and eastern Illinois as well. Dan Schaeffer with Illini FS in Tolono has reported quite a bit of black cutworm activity in Douglas County, in particular, with insecticide applications warranted in several fields (3% or more of the plants cut). In at least one field, third to fourth instars were drilling into the bases of 2-leaf-stage corn and killing the growing points, the type of injury that is more common with both older cutworms and corn plants.

Most of the black cutworm infestations have been in no-till and strip-till fields or fields with considerable weed cover (e.g., chickweed) before planting. However, there are exceptions. The field in which cutworms were drilling into the bases of seedling corn plants in Douglas County was weed-free this spring. This is only one example of the occurrence of black cutworm problems that didn't go by the book, and a strong indication that all fields of corn need to be scouted right now, regardless of the condition of the fields before planting.

According to our degree-day calculator, the black cutworm damage currently being observed and addressed in Illinois could easily be the result of eggs laid by black cutworm moths during the latter half of April, after the freezing temperatures early in the month. The first evidence of cutting activity by black cutworms can be predicted by accumulating degree-days (base 50°F) after the first significant moth flight. Black cutworm larvae become fourth instars (cutting stage) when 312 to 364 degree-days have accumulated. As of May 15, accumulated degree-days had exceeded or were near 300 in many areas of Illinois, even if moth captures were as late as April 30.

In issue 6 (May 4, 2007) of the Bulletin, we provided a table of insecticides suggested for control of black cutworms in corn in Illinois. Thus far we have received no reports of "rescue insecticides" that have failed to provide control of black cutworms; soil conditions have been ideal for effective control in most areas. As we have stated in the past, we are always interested in learning about efficacy of all products registered for control of black cutworms, so don't hesitate to contact us to share your experiences.--Kevin Steffey and Mike Gray

Kevin Steffey
Mike Gray

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