June 23, 2004

Soybean Aphid Update

The significant aphid infestation reported in a field near Mediapolis caused quite a stir, but it appears that it was a single odd occurrence. Other fields in the area also had some soybean aphids, but only a few per plant and only a few plants with aphids per field. There have been other scattered reports of aphids across the state, but most have been at extremely low numbers and in just a few spots in the fields. Some of the aphid reports have turned out to be thrips, which are common in soybeans, but usually not an economic problem.

Some are asking about including an insecticide with the Roundup application just in case the aphids or bean leaf beetles become a problem later. Now is not a good time for spraying for bean leaf beetles since we are between generations. Spraying for aphids when very few aphids are present may not only be a waste of money but might actually make the aphid problem worse by killing off the beneficials that are keeping the aphid population in check. The working economic threshold for aphids is 250 per plant.

For more information see and a link to a picture of a thrip, see the June 21 ICM newsletter at http://www.ipm.iastate.edu/ipm/icm/2004/6-21-2004/soyupdate.html. For your reference, there is a very nice 1 page publication from the University of WI that covers aphid thresholds and stage of development of soybeans. Go to: http://www.plantpath.wisc.edu/soyhealth/aphids/uwexsoystage.pdf

Flumioxazin Injury to Soybeans

Several soybean fields in the area have showed some injury problems from flumioxazin (Valor, Gangster). In a few cases the fields had to be replanted. Some of the injured soybeans were showing symptoms similar to dicamba injury (cupped leaves). For more information see the following article by Bob Hartzler: http://www.weeds.iastate.edu/mgmt/2004/ppoinjury.shtml

Soybean Damping Off

Some of the damping off of soybeans that is now occurring in the area may be due to Phytophthora rather than Pythium. If the soybeans are replanted, variety selection is important if the damping off is being caused by Phytophthora. Many Phytophthora resistant varieties use the "Rps1K" gene, which is not effective on several new races. If this is what is present in the affected variety, the replanted variety should contain the Rps-6 gene instead. See X.B.'s recent article for more information: http://www.ipm.iastate.edu/ipm/icm/2004/6-21-2004/phytop.html.

How Late Can Nitrogen Be Applied to Corn?

The wet weather has delayed the N application in some corn fields and has resulted in nitrogen losses in other fields where the soil has been saturated. Corn can benefit to N applications even as late as tasseling if the soil is deficient. If no nitrogen has been applied or the corn is showing N deficiency symptoms, about 60-80 lb/A could be dribbled between the rows. Lower amounts might be sufficient if N has already been applied and corn is somewhat pale in color but not severely deficient. The July 2, 2001 ICM Newsletter has more information at http://www.ipm.iastate.edu/ipm/icm/2001/7-2-2001/nottoolate.html

EVENTS IN THE NEAR FUTURE TO GET ON YOUR CALENDAR

June 24 NE Iowa Spring Field Day, Nashua
Lunch and Static Displays 12:00 1:30PM ; and wagon tours from 1:30 4:30 PM.

June 28 Pasture Walk - Benton County 6:00 p.m.
Don Newton farm, corner of 18th Ave. Dr and 75th St. Dr. north of Blairstown. Discussion will focus on typical Iowa creek pasture concerns; weed control, improving stands, rotational grazing options.  Free meal at 6:00.

June 29 Soybean Rust Update, Johnson County Extension Office, Iowa City 9:00 a.m. to noon
This morning meeting will be a multi-state distance education program that will bring together the most knowledgeable people on the subject in the United States to provide insights on the status of the disease, most likely scenarios for it to move to North America, distinguishing between soybean rust and other leaf diseases, and the process that is in place to monitor for the disease and confirm its presence when it arrives.  This meeting will NOT train CCAs to be first detectors.  The fee is $10 for non-CCAs and $35 for CCAs attending for credit. Please send me an e-mail note by June 28 if you plan to attend.

July 6 Pasture Walk - 6:30 pm - Iowa County
Amana Farms, pasture on the north edge of the visitors center, meet at the visitor center/RV park in Amana.  Tall fescue is an increasing pasture problem in eastern Iowa.  This pasture walk will focus on identifying tall fescue, managing fescue pastures and animals grazing fescue, featuring Dan Morrical, ISU Extension Sheep/Forage Specialist.

July 8 First Detector Training For Asian Soybean Rust - Montgomery Hall, Johnson County Fairgrounds

This program is for Certified Crop Advisors and Certified Professional Agronomists to train them to become "first detectors" to learn how to identify soybean rust. There is no pre-registration for this meeting. The fee is $20 (made out to ISU). CCA credits are available.