August 10, 2008
State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246
Soybean Aphid Update - Many Fields Over Economic Threshold
fields are over the economic threshold of 250 aphids per plant (& 80% of plants infested) and spraying has been going
strong for over a week north of I-80. Some fields have now also reached
the threshold in the south. It is obvious that this will be a worse year for
aphids than what we experienced two years ago. Some have seen aphid
numbers decline recently in fields that haven't reached the threshold,
so fields need to be scouted to determine whether an insecticide treatment
is justified. The hot weather may be doing some good. Some studies have shown
that soybean aphid's rate of reproduction slows with temperatures
above 86F and stops at 95F. Heavy rains may reduce aphid numbers somewhat,
but it is not likely that rains will solve the problem. Many are using a
combination of about a 1/3 rate of Lorsban plus
2/3-3/4 rate of a synthetic pyrethroid. The Lorsban gives a quick kill and can help to prevent spider
mite outbreaks and the pyrethroid gives longer
residual. August is a critical month for soybeans so its
important to protect those good potential yields out there, especially
with the price of beans today.
is best to count all aphids on a few plants to get a feel for what 100 and 250
look like and then estimate from that point on. Another method of scouting
developed at the
insecticide trial results on aphids can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html.
See the latest
Asian Soybean Rust
X.B. Yang now predicts that there is a greater than 50%
Other Soybean Diseases
The high humidity has been good for white mold development and problems are now showing up in some fields. Sudden death is also apparent in some fields.
FOR YOUR CALENDAR
White Mold, Managing Rotation Resistant Rootworms & Fungicides on Corn Discussed at
Corn and soybean disease management and managing rotation resistant rootworms will be featured at the Dean Folkman farm just east of Newhall (just west of Linn Coop). X.B. Yang will discuss the results of a white mold fungicide trial on the farm and give a soybean rust update. Early observations about fungicides sprayed on corn this year will be discussed as well. Patti Prasifka, ISU Entomologist, will discuss the results of the rotation resistant rootworm monitoring that has been done in the area this year as well as management options for the problem. BASF and Linn Coop. will be providing a free meal and 6:00 p.m. followed by the tour.
Fall Field Day
September 6 - 1:30 p.m.
Topics will include grain storage issues, grain marketing, low linolenic soybeans and other alternative crop opportunities, and managing extended diapause northern corn rootworms.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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