July 17, 2008
CORN & SOYBEANS
Beetles were reported on ornamentals in
In soybean, the economic threshold for the beetles is the general leaf defoliation threshold used for other pests. During the reproductive stages of soybeans, the threshold for considering an insecticide treatment is if greater than 20% of the leaf area is gone due to feeding. However, the high price of soybean may lower the threshold slightly. But remember that most people tend to overestimate defoliation. If it looks like 20% defoliation, most likely it’s only 10%. The pictures in the following article can help in estimating percent defoliation: http://www.ipm.iastate.edu/ipm/icm/2002/7-29-2002/soydefoliation.html.
In corn, Japanese Beetle adults feed on leaves, tassels, silks, and pollen and are capable of interfering with pollination With later-than-usual pollination this year, silk clipping may be more of a threat than usual. If silks are being clipped to within 0.5 inch of the end of the ear and pollination has not yet occurred, consider and insecticidal treatment.
For more information and insecticides labeled for Japanese beetles see the July 28, 2003 ICM Newsletter at http://www.ipm.iastate.edu/ipm/icm/2003/7-28-2003/japanesebeetle.html.
The higher grain prices are increasing interest in trying to boost yields with foliar fertilizer.
Antonio Mallarino, ISU Extension Soil Fertility Specialist, has extensively tested foliar fertilization of soybeans recently. Although he occasionally obtained yield boosts of 5 bushels per acre or more, the average yield increase he obtained with foliar fertilization was less than 1 bushel per acre. For more information, see Antonio’s article in the ICM News at http://www.extension.iastate.edu/CropNews/2008/0703Mallarino.htm.
work has been done on foliar fertilization of corn. Two items worth reviewing are from John
Sawyer, ISU Extension Soil Fertility Specialist, and others, at http://www.agronext.iastate.edu/soilfertility/info/foliarfert99.pdf
and from Robert Dobbs and others,
have not yet personally observed any soybean aphid activity in any of the
counties I cover. However, a very
credible scout reported finding a few small colonies in one soybean field in
Soybean aphids tend to not be a problem in even-numbered years, and, so far, it looks like 2008 will continue the pattern. If the pattern does continue, there may still be a few fields with economic injury, so looking for this pest during routine scouting is advisable. The economic threshold is 250 aphids per plant with 80% of the plants being infested and with populations increasing. Spraying too early can actually make the problem worse by killing the beneficial insects that are helping to keep the population in check and may increase the likelihood that the field will need to be sprayed later. Scouting techniques and management information can be found in SP 247, Soybean Aphids in Iowa – 2007, which can downloaded from http://www.extension.iastate.edu/Pages/eccrops/transfer/07SBA.pdf.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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