The wheat situation as of April 12, 2013, remains a tough one to grasp, but that could be because we might not really want to. The wheat this season has been through a lot. Top upon the list of wheat woes is the current drought. Add to that a fairly common occurrence of mosaic viruses, several nights of prolonged cold weather recently, and a spotty but heavy greenbug situation and the prognosis for area wheat cannot be too exciting. There are a few exceptional fields in the area, but these tend to be fields where wheat is the producer’s primary crop and are fairly rare.
In my on-site wheat inspections this week I still find a substantial number of greenbugs in most fields. I urge consultants and producers alike to get an eye in any questionable fields as populations are variable from field to field. In many cases these greenbugs are well over the economic threshold in remarkable numbers, in other cases the predators seem to be controlling them well. The ‘greenbug clouds’ that myself and several area entomologist reported seeing last week seem to have subsided. The aphid situation might be stabilizing, but if a field has an economic pest population and that field’s economic situation still looks to have some potential, now is the time to act.
To check for wheat aphid pests, I prefer to use a drop cloth or clipboard in a beat sheet type method during the hottest part of the day, on an already warm day. Aphids will be harder to find on cool or cold days or mornings. The darker the color of the clipboard or cloth the better the aphid pests will stand out and be seen. I fold the drop cloth so it is roughly the size of a clipboard and lay the cloth (or clipboard) on the ground along planted ‘row’ or wheat as flat as possible. Then I vigorously pop the wheat onto the drop cloth, shaking the aphids onto the cloth trying no to do much harm to the aphids, while still shaking them loose. Once you feel all aphids are off the wheat, get a full count of all aphids and good species identification. Don’t forget to get a good evaluation of the beneficial arthropods at this time. Even with some pretty high existing aphid numbers, a good population of ladybug larva, parasitic wasps, and lacewing larva give can adequate control if present in high enough numbers. I also like to make at least a cursory look over the wheat plants just utilized in the drop sample for pest damage and the presence of mosaics. Often I will dissect several plants while I am there to check for cold damage and head size at this time too.
A full explanation of greenbug and other aphid wheat pest economic thresholds can be found in the Texas A&M AgriLife Extension wheat pest publications. A good rule of thumb I have used is; if your field is averaging 70-100 greenbugs per clipboard sized beat sample, and few predators can be found, you might be near ET for that field. This is roughly based upon Extension data, but does not take into account grain price.
I feel a larger question remains for many area wheat producers… Even if my field is at ET for any pest aphids, is it really worth spraying?
That is a good question, but one that can only be answered on a field by field basis. This next week we will have several decisions to make. Another question is… Did your field receive cold injury this last week?
Unfortunately it will not be until next week before we will be able to tell if a field has sustained economic cold injury to the head and main growing point. To give us a hand with that, Dr. Calvin Trestle, Agronomist – Texas A&M AgriLife Extension – Lubbock, will be making a whirlwind tour of the District 2 wheat growing areas on April 17th. He will be stopping at the Street Community Gin in Claytonville, Texas at 5PM on that date. Wheat producers are encouraged to bring samples from your fields for him to dissect and to train producers on how to do it themselves. I will be out of town next week until the 19th. At that time, I would be more than happy to help determine the viability of any wheat field, aphid pressure, or any other IPM question you may have.