Northwest Iowa Crop Update Newsletter by Todd Vagts ISU Extension Crops Specialist Counties Served:  Carroll, Calhoun, Crawford, Ida, Monona, Pocahontas and Sac.
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Volume 2, Number 12

Northwest IA Crop Update, June 10, 2002
(Word Document)

Introduction
The warm and windy conditions continued across most of western Iowa last week.   Corn and soybeans have really taken off as well as weed emergence and growth.  Corn development has moved past the 6 leaf stage, marking the beginning of the period of rapid growth and nutrient uptake.  Root disease has shown up in some corn fields, look for diseased mesocotyls.  Soybean development ranges from V1 to V2.  Stalk borer migration should be occurring across central IA.  Most alfalfa has been cut, be on the lookout for regrowth problems due to insect feeding.

Weather update
Rain and mild temperatures is forecasted through Wednesday of this week, then dry and mild conditions through the 10-day forecast.  West-central IA picked up only scattered showers last week, unlike eastern IA where 3 to 8 inches of rain was more common.  The next 10 days should be perfect corn and soybean growing conditions

Growing Degree Day Accumulation and Crop Development
Northwest IA picked up 134 Degree-days (base 50) last week and is forecasted to pick up 141 this week.  NW Iowa has been accumulating greater than normal DD50’s over the last two weeks and has made up for the shortfall in May (Figure 3)

Corn Development   The majority of corn is at or shortly past the V-6 leaf stage.  This marks the beginning of a period of greatly increased stalk elongation and nutrient uptake.  The nodal root system is becoming the major functioning root system.  Total uptake of nutrients has been small through the 6^th leaf stage of corn (N = 8lbs, P = 5 lbs, K = 8 lbs).  But rapid accumulation of nutrients and plant dry matter will occur from V6 through V18.

Soybean Development  Soybeans range from V1 (1 node) to V2 (2 nodes) and are growing well in most areas.  New V stages will appear about every 5 days through V5 and every 3 days through R5.  Growth stages of soybeans are defined by the uppermost fully developed leaf node.  A fully developed leaf node is one that has a leaf above it with unrolled or unfolded leaflets (leaflet edges are no longer touching). 

 V2 Stage Soybeans  Nodule formation occurs shortly after VE, but active nitrogen fixation does not begin until the V2 to V3 stage.  Lateral root development is rapid at this point through the upper 6 inches of soil (cultivation and field traffic can damage this developing root system)

In Figure 2, the line with squares equates to Monona, Crawford, Carroll and southern Ida, Sac and Calhoun counties.  The line with Diamonds equates to Pocahontas, Buena Vista and northern Ida, Sac, and Calhoun counties.  The dotted line is predicted GDD and crop development in 7 days.

Pest Management
Stalk Borer Migration  Stalk borers may be leaving areas of tall grass (ditches, waterways, fence lines, etc.) for the edge rows of corn fields.  Scouting should begin when 1,300 - 1,400 Degree Days (Base 41) have accumulated. Based on current degree-day accumulation, the area south of Hwy 20 is currently at 1378 DD41’s and north of Hwy 20 is at 1240 DD41’s.  Northwest IA is forecasted to accumulate 160 DD41’s over the next 7-days.

 Weed Control in corn and soybean fields should be a high priority for many producers across northwest IA as weed emergence and growth has really taken off over the last couple of weeks.  For excellent, in-depth information on post-emerge weed control options in corn and soybeans, refer the following web sites: 

·         Iowa State University ICM Newsletter 5/14/2001 “Post emergence grass control in Corn”
http://www.ipm.iastate.edu/ipm/icm/2001/5-14-2001/postemerg.html

·         Iowa State University ICM Newsletter 5/20/2002 “Preventing early season weed competition”
http://www.ipm.iastate.edu/ipm/icm/2002/5-20-2002/earlyweed.html

·         University of NE Crop Watch, June 7 Edition “Post emergence herbicides for soybeans”  and “Row Spacing Influences Weed Control Timing:  http://cropwatch.unl.edu/

·         Michigan State University CAT 5-23-02  “Selected characteristics of several post emergence herbicides for corn”  http://www.msue.msu.edu/ipm/CAT02_fld/FC5-23-02Herbicide.htm

Corn Root Disease Problems  I’ve noticed a few fields with root disease and other areas of Iowa have reported the same problem; primarily infection and decay of the seminal (seedling) roots and mesocotyl (area between the seed and nodal root system).  Decay can usually be attributed to Pythium, Fusarium, Diplodia, or Rhizoctonia.  Pythium-rotted roots are usually soft and dark colored.  Roots rotted by Fusarium will be firm or shriveled and tan to pink colored.  Rhizoctonia rot is firm and brown to reddish brown and may be in distinct lesions on the mesocotyl.  (ISU publication PM-596).  Infected plants my be stunted, wilted and purples in color due to reduced water and nutrient uptake.  Once the nodal root system takes over, the infected plants should resume development as long as they are not in competition with larger, healthier plants.  For more information, refer to this 1999 ICM newsletter article http://www.ipm.iastate.edu/ipm/icm/1999/6-14-1999/cornseedlprob.html

Alfalfa Regrowth should be scouted for alfalfa weevil and variegated cutworms.  Last year we had problems with regrowth due to variegated cutworms, particularly where the windrow sat.  If the alfalfa doesn’t green up normally, look for cutworm activity on the crowns and in the litter surrounding the crowns.

(Word Document)