July 25, 2007
 

Iowa State University Extension Information for Southeast Iowa
By Jim Fawcett, ISU Extension Field Agronomist
4265 Oak Crest Hill Rd. SE
Iowa City, IA 52246
319-337-2145

CORN

 

Rotation Resistant Rootworms

          Root feeding by rotation resistant rootworms played a role in causing some of the lodged corn during last week’s storms. In most cases it is the northern rootworm beetles that are being observed in these fields, indicating that it was likely extended diapause populations from eggs laid two years ago that is causing the problem. Emergence traps were placed in several eastern Iowa corn fields this on soybean ground this month to try to get a better feel of how widespread a problem we have with both the extended diapause northern population and the western variant that is laying eggs in soybean fields. Flattened corn has partly goosenecked back up, but most of the straightening has been above the ear.

 

SOYBEANS
 
Soybean Aphid - Spraying Has Begun

 

 Brian Lang reports that many fields have been sprayed in Winneshiek, Clayton, and Allamakee counties in NE Iowa, with some fields having over 1000 aphids per plant. Spraying has also begun in the northern part of east central Iowa, with some fields over the economic threshold in Jones County, and some fields in Linn and Benton counties getting close to the economic threshold. Aphid numbers can vary substantially from field to field, so it is important to scout now and not spray unless the threshold of 250 per plant (& at least 80% of the plants infested) is reached. If fields are sprayed too soon, it is more likely that they will have to be re-sprayed. It is also likely that many fields will not reach the economic threshold.

I am a little surprised to be seeing spider mites in quite a few fields, considering that most of the area has received ample rainfall. The two week stretch of hot, dry weather must have allowed populations to build up. Although the level of infestation is low, if spider mites are found in a field that is going to be sprayed for aphids, it would be best to use a product that controls both pests, such as Lorsban, to avoid spider mite outbreaks.

It 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 University of Minnesota that can help to speed up the process can be found at http://www.soybeans.umn.edu/crop/insects/aphid/aphid_sampling.htm.

Some insecticide trial results on aphids can be found at http://www.ipm.iastate.edu/ipm/icm/2006/1-23/insecticide.html. See the latest Iowa aphid information at http://www.ipm.iastate.edu/ipm/icm/2007/7-16/soybeanaphid.html

 

Asian Soybean Rust

 

The threat has increased that we may eventually see some Asian soybean rust this year in Iowa, although the chances are still less than 40%, according to X.B. Yang. Widespread problems with rust are now being found in northern Texas, and X.B. reports it will likely be found in Oklahoma soon. It has also been found for the first time this year in Arkansas. Because of the increased risk for Iowa, sentinel plots in the state will be monitored more frequently in August. Hopefully if it does arrive in Iowa it will be late enough in the season so the impact will be minimal. For the latest on where rust (and aphids) is being found see http://www.sbrusa.net/. Click on the little arrow next to soybean aphid in the upper right corner to change the map to aphids.

 

 

FOR YOUR CALENDAR
 

Midwest Strip Till Conference - July 31 9 a.m. to 3:00 p.m.
Waterloo
 

Organized by Research and Extension of Iowa State University, the University of Minnesota, the University of Wisconsin, and Hawkeye Community College. Manufacturers will demonstrate equipment for strip-tillage and associated operations, including auto-guidance systems and fertilizer injectors.  Researchers, farmers, and industry representatives will present the latest information on strip-tillage related topics, including equipment selection, fertility management, and guidance technology. Participants will review information booths all day, and lunch is available on site.  This program is free and open to the public. Five Certified Crop Advisor CEUs (4.5 SW & 0.5 NM) will be available for a nominal fee.  Expo details are at: http://wrc.umn.edu/outreach/striptillageexpo/midwest/index.html

Soybean Aphid and Bean Leaf Beetle Management Tour - August 8 - 6:30 p.m.

Washington County
 

Management techniques for the soybean aphid and bean leaf beetle will be highlighted at a tour on the Iowa Learning farm site on the Rob Stout farm south of West Chester on Wednesday, Aug. 8. Since first being discovered in the Midwest in 2000, soybean aphids have tended to be more of a concern in odd numbered years, so this may be more of a pest this year than last. No-till soybean plots that were planted with and without the seed treatment “Cruiser” are the focus of research conducted on this Iowa Learning Farm site. Seed applied insecticides can provide good early season bean leaf beetle control and also provide some control of soybean aphids, especially when planting is delayed as it was this spring. Also discussed at the tour will be value added crop opportunities, including “low lin” soybeans. A rain simulator will also be demonstrated at the site. A free meal, courtesy of QUALISOY (http://www.qualisoy.com/) will be available at 6:30 p.m. followed by the tour. The Iowa Learning Farm project is a unique partnership of agencies, farm and conservation groups, the general public and Iowa State University. Iowa Learning Farm project staff work to increase the adoption of residue management and conservation practices that are expected to improve water quality.
 

Pest Management Tour - August 27 - 6:00 p.m.

Benton County

Corn and soybean disease management and managing rotation resistant rootworms will be featured at the Dean Folkman farm just east of Newhall. 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.