July 17, 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

 

Storm Damage

 

Although the rain was needed, we could have done without the wind and hail. Fortunately most of the downed corn appears to be due to lodging rather than green snap, so it’s not quite as bad as it looks right now. The corn will partially straighten up in the next few days. Most of the stalk straightening will occur near or above the ear leaf, making harvest a challenge. Some research at the University of Wisconsin indicated about a 15-30% yield loss when corn is flattened at the pollination stage. There were also smaller areas where hail damage occurred. About one third of the corn yield is lost with a 50% loss of leaf area at silking. Assessing Hail Damage to Corn (NCH-1) http://www.extension.iastate.edu/Publications/NCH1.pdf can help in estimating potential yield losses. Of course it’s important to get the insurance person out to look at corn and soybean fields if you have hail insurance.  Lodging and hail also increase the incidence of plant diseases, including stalk rots. See Roger Elmore’s 2005 ICM article for more discussion on corn lodging at http://www.ipm.iastate.edu/ipm/icm/2005/8-1/rootlodge.html.

 

Nitrogen Deficiency

 

Nitrogen losses from the heavy rains that occurred 2 or more weeks ago are showing up in fields now. If nitrogen is short, deficiencies show up in the older leaves as the developing ear gets preferential treatment. Some yield increases have been seen with additional nitrogen applications up until VT (tassel emergence), but the odds of a response go down fairly rapidly after that time.

SOYBEANS
 
Soybean Aphid

 

Soybean aphid numbers are increasing in the area, but are still at low levels in most fields. I’ve been finding an average of less than 1 to about 10 per plant. The economic threshold is greater than 250 per plant on at least 80% of the plants. This threshold is set to prevent the economic injury level of about 700 per plant from being reached. It’s important to give the beneficial insects a chance and not just spray at the first sign of aphids.

 

 

FOR YOUR CALENDAR
 
Ag Professional Tour – July 20  9:30 a.m. to noon
NE Iowa Research Farm – Nashua
 

Emphasis on current crop and pest issues with tour of on-farm research trials. CCA credits available.
 

 
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
 

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.