Vol. 1 No. 4

Todd Vagts
Iowa State University Extension
Field Crops Specialist
1240 D. Heires Avenue Office: 712-792-2364
Carroll, IA 51401 Cell: 712-249-6025
Email: vagts@iastate.edu Fax: 712-792-2366

Northwest IA Crop Update, May 7, 2001

In this issue

Growing degree accumulation update

Scout for Black Cutworms soon

Late application of preemerge herbicides and UAN

Introduction

Many are back in the fields this week, finishing up corn planting and moving into soybeans. The weather forecast looks to be fairly open, with warm (hot) days and only a chance of scattered showers across the region for the next several days. Fields in Calhoun, Pocahontas and Buena Vista counties are still drying out from rains over a week ago. It appears that corn survival in these wet and flooded areas will be fairly high. Low spots that sat under water for over five days appear to be at the highest risk. Continue to monitor these fields for emergence problems and damping off once the corn has emerged. Rotary hoeing has been necessary in many corn fields due to crusting and to reduce the potential for blowing soil and sand. A recent article in the Iowa State University ICM newsletter provides more detailed information on rotary hoeing, this information can be obtained at the website http://www.ipm.iastate.edu/ipm/icm/2001/5-7-2001/hoecrust.html . Most corn in the eight county area is in the V1 to V2 stage and some of the earliest soybeans planted are just emerging. Over-wintered Bean Leaf Beatles are emerging and can be found in corn fields with soybean stubble and emerging soybean fields.

Weather update

Scattered showers moved across the area over the last week, but most counties in NW Iowa received only minimum rainfall amounts. Most rainfall has now been centered over southern and eastern IA counties, greatly slowing fieldwork in those areas. Dr. Elwynn Taylor predicts a fairly favorable week for field work across NW Iowa. He predicts the next major storm system to reach IA by Thursday but the moisture prospect from the system is still unknown. The last three-day’s and the forecasted 72-hour average soil temperature can be accessed online at: http://extension.agron.iastate.edu/NPKnowledge/

Crop Development and Update

From my calculations, corn planted up through April 27 should be emerged across most of the area. Corn typically requires 110 GDD50’s for emergence. As in most cases, this number will vary depending on soil temperature, soil type, planting depth, and soil moisture. The cloudy days and excessively wet soils most likely will delay emergence. The accumulation of 200 DD50’s indicates there should be some corn in the V2 stage, which may be the case with the earliest planted corn in some counties.

Pest Management

Alfalfa weevil: Alfalfa weevil scouting should continue across the area. No major feeding injury has yet been reported in NW Iowa. For more information on Alfalfa Weevil go to http://www.ipm.iastate.edu/ipm/icm/2001/4-30-2001/alfscout.html

Black Cutworm: We have accumulated enough GDD in NW Iowa to begin scouting for black cutworms. Scattered reportes of Black Cutworm feeding has been reported in southern Iowa counties, but most of this feeding is from the Dingy Cutworm, which normally does not create economic problems in Iowa corn field. Corn is typically safe from BCW activity once it is past the V5 stage. For more information on cutworm scouting refer to http://www.ipm.iastate.edu/ipm/icm/2001/5-7-2001/earlyscout.html.

Bean Leaf Beatle The majority of BLB over-winter in or near wooded areas where they can find good cover. Yet up to twenty percent may remain in the soybean stubble. You may find these beetles on corn plants planted into last year’s soybean fields. BLB typically will not feed on corn plants. The presence of BLB indicates that we did have a population survive the winter and may cause problems this spring and summer. Late planted soybeans may be our best method of reducing the overwintered population by not providing a food source when they emerge. Economic injury to soybeans typcially does not occur until the second generation in August, yet with higher than normal populations the last couple of years, severe feeding injury on soybeans has been observed from the overwintered and first gerneration beatles. Additionally, the beetle transmitts the Bean Pod Mottle Virus (BPMV) which alone, can cause yield reducing injury to a soybean field. BLB samples were collected last fall and recent results indicate that most of the beetles were carrying the BPMV. This would indicate that the BPMV could be a problem again this year. The best way to control the BPMV is to control the BLB. If you suspect that you had BPMV last year, you may consider an early season insecticide application on the soybean field to prevent transmission of the virus by the feeding of the over-wintered beetles.

Weed emergence: Expect to start finding Yellow foxtail, Black nightshade, Common cocklebur and Wild proso millet in the field. Emergence of these weed species begins after an accumulation of 250 DD50’s. An excellent resource for weed seedling identification can be found at http://www.weeds.iastate.edu/weed-id/weedid.htm

Soils and Soil Fertility

Broadcast postemergence Urea-Ammonium Nitrate (UAN) solution application by John Sawyer.
Broadcast postemerge application of UAN (28 and 32% urea-ammonium nitrate solution) to corn has the potential to cause phytotoxic symptoms of leaf burn, necrosis, loss of leaves, and plant stunting. Burn symptoms will be visible within 24 to 48 hours after application. With hot-dry conditions, appearance of darkened leaf tissue can begin within a few hours. Depending upon the severity of damage, reduced plant growth may be visible for several weeks after application. Research conducted by Dr. Gyles Randall in Minnesota indicated that when corn plants are at the V3 growth stage damage was not permanent and did not adversely affect stand or yield. When plants were larger than the V3 stage, plant damage was worse and some yield depression occurred with the 120 lb N/acre UAN rate. Conservative suggestions to avoid yield loss are to not exceed postemerge UAN rates of 90 lb N/acre when corn is at the V3 to V4 stage, 60 lb N/acre at the V7 stage, and to not apply UAN to foliage if plants are larger than the V7 stage. Hot-dry weather conditions will increase leaf burn and plant growth reduction. Refer to http://www.weeds.iastate.edu/mgmt/2001/nitrogenfert.htm for more information.

Soil compaction. The biggest single cause of compaction in a given field is the degree of wetness when work is performed on that field. Approximately 80% of soil compaction in a field is caused by the first trip over the field. Soils that are too wet provide the lubrication needed for soil particles to be compressed together, destroying aggregates and reducing air space. Compaction has a limiting effect on yield by decreasing rooting depth and density.

For further information pertaining to this newsletter, please contact me or any of the area extension offices. If you would like this letter to be emailed directly to you, please send an email with the desired email address to vagts@iastate.edu.

This page last updated on 02/03/04

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