June 4, 2007

 

CORN

 

Insect Problems

 

Black Cutworms

 

Although corn fields that I have scouted have not had black cutworm damage above the economic threshold, Mark Carlton reports that there has been extensive cutting in some fields further south. Corn should continue to be scouted for cutworms until V5 (when five leaves have fully emerged from the whorl). The economic threshold is 2-3% of the plants cut or wilting when the cutworms are less than 3/4 inch long, or if cutworms are longer than 1 inch, the threshold is 5% of the plants cut.

 

White Grubs

 

I have found some corn stand losses from white grubs in the area. True white grubs have a 3-year life cycle, so feeding can continue throughout the season and stand losses are common. If replanting is justified, an insecticide seed treatment should be used to protect the replanted corn. At this late date it would likely take stands of less than about 18,000 plants per acre to justify replanting, depending on the uniformity of the surviving stand and cost of replanting. Annual white grubs usually pupate before they do enough damage to justify replanting.

 

The grub of the Japanese beetle has been an increasing problem in corn fields in the past few years, especially near urban areas, such as Cedar Rapids, where the Japanese beetles are more numerous. This grub also has an annual life cycle, so does not cause as much damage as the true white grub. To tell the difference between the true white grub and annual grubs, you need to use a magnifying glass and look at the raster (hair) pattern on the tail. The true white grubs have rows of hairs that look like a zipper, whereas with the annual grubs the hairs occur more randomly. See the May 15, 2006 ICM Newsletter for a picture of the true white grub raster pattern:

http://www.ipm.iastate.edu/ipm/icm/2006/5-15/insects.html

 

Millipedes

 

Millipedes are being found in high numbers in some fields. Although millipedes usually do not feed on living plants, they have been known to cause stand losses in no-till corn and soybean fields under cool, wet conditions where crop residue levels are high. Although broad spectrum insecticides may kill the millipedes, a better way to manage the problem is to use residue managers to try to reduce the amount of residue left over the crop row.

 

Nitrogen Losses

 

The recent rains have likely resulted in more losses of nitrogen in corn fields. On most Iowa soils (silt or clay loam) most of the losses are due to de-nitrification rather than leaching. Research conducted in Illinois with late May to early June excess application of water on silt loam and clay loam soils indicated approximately 4 to 5 percent loss of nitrate present per day that soils were saturated. An additional 50 lb/A or so of nitrogen may be justified in fields where soils have been saturated for a week or more. It’s not too late in many fields to pull some soil samples for the late spring soil nitrate test to confirm whether losses have occurred. Soil samples should be pulled to a one foot depth when the corn is 6-12” tall. It is best to use a systematic method rather than a random method to pull the samples. Pull the first sample in the corn row, the next 1/8 of the distance between rows, the next ¼ the distance between rows, etc. until you have worked your way across the rows. Do this at least twice for a total of 16 cores. This way you won’t by chance happen to be over or under representing areas that have higher bands of nitrogen (ie anhydrous bands, manure bands, starter fertilizer). Soil samples should be sent to a lab immediately after sampling. For more details see the publication “Nitrogen Fertilizer Recommendations for Corn in Iowa” at http://www.extension.iastate.edu/Publications/PM1714.pdf

 

SOYBEANS

 

Asian Soybean Rust

 

Sentinel plots in Iowa will be scouted intensely soon and I am already monitoring a spore trap at the research farm at Crawfordsville. There have been finds in kudzu in Louisiana and Texas, as well as in Florida. To monitor the rust situation see http://www.sbrusa.net/

 

 

FOR YOUR CALENDAR

 

Help Celebrate ISU’s 150^th Birthday With Jack Payne at the

SE Iowa Research & Demonstration Farm Spring Field Day - Crawfordsville

June 21

 

Doors open at 11:00 with a free health screening and displays on alternative energy, the bioeconomy, and trading carbon credits. A free lunch, courtesy of Farm Credit Services, is available at 11:30. Jack Payne, ISU Extension Vice President, will be speaking at 12:15. The farm tour begins at 1:00, where the stops include:

 

¨     Crop Season Review & Marketing During Volatile Times– Kevin Van Dee, Farm Superintendent & Jim Jensen, ISU Farm Management Specialist

¨     Fungicides on Corn & Asian Soybean Rust Outlook
Daren Mueller, ISU Extension Plant Pathologist

¨     Moving CRP to Crops – Carbon Sequestration Impacts
Mahdi Al-Kaisi, ISU Extension Agronomist - Soil Management

¨     Bt-Rootworm Hybrid Results & Rating Corn Roots
Jon Tollefson, ISU Extension Entomologist

 

CCA Credit Opportunity – June 21 - Crawfordsville

 

Earn 5 hours of CCA credits, including 2 hours in soil and water, by attending a special CCA session beginning at 9:00 a.m. followed by the afternoon field day. The morning session will include:

 

Ø     Alternative Crop Research in Iowa   

Jim Fawcett, ISU Extension Crop Specialist

 

Ø     Soil Bulk Density and Water Infiltration Rates with Different Tillage Systems

Mahdi Al-Kaisi, ISU Extension Agronomist – Soils

 

Ø     Fungicides – Review of Products & Research Results in Corn & Soybeans - Daren Mueller, ISU Extension Plant Pathologist

 

There is a $50 registration fee ($70 after June 19). Give the Johnson County Extension Office a call or send me an e-mail note if you plan to attend. You can pay at the door.

 

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 meal 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.