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Issue No. 2, Article 3/April 4, 2008

Preparations for Early-Season Insect Activity

Over the years, I have learned that predicting the occurrence of insect problems, or the lack of them, is not very wise, so I usually try to avoid it. One thing is certain, however--early-season insect problems will occur in some fields in some parts of the Midwest in 2008. How's that for an enlightened statement?

All kidding aside, it is likely that most growers and their advisers have already given thought to dealing with early-season insect problems, from the secondary insects that attack corn in the spring (e.g., black cutworms, grape colaspis, white grubs, wireworms) to alfalfa weevils in alfalfa to aphids and armyworms in wheat. Every one of these insect problems, and many others, have likely affected fields in your area over time, so thoughts on management often are foremost in the spring after alfalfa and wheat resume growth and after corn seeds is in the ground. Following are comments about insects that attack crops early in the spring.

Alfalfa. The primary insect of concern among alfalfa growers before the first cutting is the alfalfa weevil. This insect has not been a widespread problem in Illinois over recent years, but its presence (or absence) is always worth investigating. We will learn soon enough whether the harsh and unpredictable winter weather has had any impact on overwintering adults and eggs in southern Illinois. (Phil Mulder, extension entomologist at Oklahoma State University, has indicated that populations of alfalfa weevil eggs in Oklahoma were much lower in early 2008 than in 2006 and 2007: www.ento.okstate.edu/pddl/2008/PDIA7-2.pdf.) Nonetheless, people should make plans in advance to scout for these defoliators relatively soon.

Most experts suggest that scouting for alfalfa weevils should commence when about 150 to 200 degree-days above a threshold of 48°F have accumulated from January 1. A quick check of the "Daily Pest Degree-Day Accumulations" on April 2 revealed that as of April 1, 196, 165, and 171 degree-days for alfalfa weevil development had accumulated at Dixon Springs, Rend Lake, and Belleville, respectively. So the time for scouting for alfalfa weevils is now for southern Illinois alfalfa fields. Our fact sheet on the Web provides the necessary information to enable accurate decision-making related to alfalfa weevil management.

Corn. Obviously, corn growers' biggest concern right now is for the soil to warm up and dry out enough that field activities can begin in earnest. Consequently, concern about early-season insect problems takes a back seat. In fact, many corn growers have already made plans to manage these inconsistently occurring pests by buying seed treated with an insecticidal seed treatment (e.g., Cruiser, Poncho) or by planning to use a granular or liquid soil insecticide to prevent insect attack. We will have to wait a little while to find out whether any of the so-called secondary insects create headaches after the corn is planted, but it's not too early to encourage plans for scouting as soon as seedlings begin to emerge. This advice goes for all fields, even those protected with insecticides (seed-applied, granules, liquids). Many corn growers have learned firsthand that heavy infestations of white grubs or wireworms can overcome the claims for their control on insecticide labels. If such a situation arises, a quick response could be the difference between profit and loss.

Wheat. Aphids likely will be the first insects noticed in spring wheat fields, though their presence then typically doesn't mean much. They usually do not cause much injury to wheat on their own unless numbers are extremely high. A working guideline from the University of Kentucky is to treat wheat in late spring only if large numbers of aphids are present or if there is an average of 50 or more aphids per head during grain filling (basically guidelines for a few weeks from now).

The other potential early-season pest of wheat, and the insect pest of greatest concern in Illinois during most years, is the armyworm. However, this insect does not overwinter in Illinois, and its arrival here as moths this spring has yet to be documented. So we still have some time before any real concerns with armyworms. Read more about them on our IPM web site.

As reports of any of these insects are received, we will spread the word. I invite anyone who becomes aware of isolated or widespread problems with early-season insects to contact either me or Mike Gray. Such knowledge usually benefits everyone.--Kevin Steffey

Author:
Kevin Steffey

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