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Former Extension Educator, Commercial Agriculture
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Friday, April 20, 2012
Over the next week, the majority of the wheat in the southern part of the state will complete the heading and pollination process. If you are out scouting fields (as you should be), you will pretty quickly notice that many of the flag leaves are discolored, ranging from yellow-to-purple (see first image above). This discoloration is symptomatic of a viral disease infection such as barley yellow dwarf virus. Dr. Carl Bradley has written an excellent article in this week's issue of The Bulletin outlining the various causal agents of viral diseases in wheat, and what you can (and can't) do to effectively control them. In that same issue, he has an article discussing application timing and product recommendations for control of fusarium head scab.
I have also received reports, and personally observed, that true armyworms (second image above) can now be found in some wheat fields. This does NOT necessarily indicate that fields need to be treated to control this insect pest. What it DOES mean is that it is time to get into fields and do some serious scouting. The economic thresholds for armyworms in wheat is six larvae per linear foot of row. Since the larvae are often hidden at the base of the plants and under residue and crop debris, it isn't much fun scouting. You have to get down on your hands and knees and look carefully.
If you do find armyworms at threshold levels in one field, don't automatically assume that they are at threshold levels in all fields. The opposite case holds true also: if you don't find them in a field, don't assume that all fields are clean. In past years I have scouted adjacent fields, separated only by a farm lane, and found high numbers in one field and almost nothing in the other.
Also keep in mind that armyworms are attacked by a number of natural enemies, particularly parasitic wasps, and that their populations can quickly crash naturally.