Issue No. 16, Article 1/July 8, 2005
Rootworm Adults Clipping Silks in Fields with Uneven Silk Emergence
Questions related to "thousands," or even "millions," of rootworm adults clipping silks in cornfields continue. Unfortunately, not much has changed since the article "Rootworm Adults and Silk Clipping" was written for issue no. 15 (July 1, 2005) of the Bulletin. In fields in which silks are going to emerge over a period of several days, people are concerned about the timing of insecticide application, or even if an insecticide is necessary. As I indicated in last week's article, there is no standard answer to this question. However, I spoke with Dr. Emerson Nafziger, Extension specialist in crop production in the Department of Crop Sciences, about corn development, and his advice was helpful. Emerson indicated that preventing significant clipping of early-emerging silks may be more valuable than preventing clipping of later-emerging silks, especially in fields suffering from a lack of moisture. Ideally, one would wish to protect the entire pollination process from assault by insects (rootworm adults, Japanese beetles), and most insecticides registered for control of rootworm adults provide enough residual activity to do just that. However, if anyone is unsure about either end of the duration of pollination, err on the early side. If drought conditions continue, some later-developing plants might not even produce sufficient silks, or pollinated silks may not develop into kernels.
In cornfields in which silk emergence is uneven, you also likely will observe a shifting distribution of corn rootworm adults. With tassels and silks as their preferred feeding sites, rootworm adults will follow their food source, flying from early-, to mid-, to late-silking plants. Trivial movement within cornfields during this time of year is typical behavior for western corn rootworm adults. Interfield movement begins more commonly after the males and females have mated and gravid (pregnant) females begin dispersing.
Questions about insects clipping corn silks will pass very quickly, so it's important to make management decisions very quickly. Refer to the aforementioned article for a list of insecticides suggested for control of rootworm adults in cornfields.--Kevin Steffey