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 10

Northwest IA Crop Update, May 27, 2002
(Word Document)

In this issue 
GDD Accumulation and Crop Development
Corn nearing 4-leaf Stage
Dust storms in Iowa?
Late Spring Nitrate Test

Introduction
This has been quite a transition from last week into this week.  We experienced very cold temperatures, strong winds and severe dust storms through much of the week, then the weekend ushered in much milder conditions.  We are forecasted to collect almost half of the degree days over the next 7 days as we did over the last 37 days.  Currently, we have about 69% of normal accumulated degree-days compared to the last eleven years.  Corn in some fields will be approaching the 4^th leaf stage, which has some major yield implications.  Now is the time to begin planning to take the late spring nitrate test to determine the current nitrogen status of area corn fields.  Soil temperatures have been on the rise now for two weeks, soybeans should greatly benefit from this.  The University of Nebraska posted some useful tools to help determine whether to change base acres and yields (www.farmbill.unl.edu)

Weather update
What a difference a few warm days can make!  The area was relatively cool last week, but the weekend ushered in much warmer days and nights and the warm conditions are forecasted to last through most of this week.  Scattered showers covered NW Iowa helping the emergence of soybeans and helped to reduce blowing dust and sand.  No major rain events are forecasted until early next week.  With the warm and sunny conditions, this makes for an ideal time for post herbicide applications to corn.

Growing Degree Day Accumulation
Once again we came up short on Degree-Days last week (60 DD50’s) compared to what was forecasted (72 DD50’s).  But we will more than make up for the shortfall this week.  NW Iowa is forecasted to receive 132 degree-days over the next 7 days!  This is 55% of the total degree-days (210 DD50’s) the area has accumulated over the last 37 days.  According to the degree-day accumulation, emergence of corn should have occurred on fields planted through May 8 (Figure 2).  The earliest planted corn should be at the 3rd full leaf stage (count the first leaf with the rounded tip) and corn planted before May 3 should be at the two-leaf stage (200 DD).  Much of the corn should be reaching the 4-leaf stage (figure 2) by next Monday (June 3). 

The V4 stage has major implications for potential grain yield as this is the time when the ear is initiated in the growing point and the number of kernel rows is determined.  Any physiological (environmental or cultural induced) stress at this time may influence the potential size of the corn ear.  The V5 stage is also important, as this is the time when the growing point moves above the soil surface.   

Just how far behind are we on degree days?  Figure 3 shows cumulated degree days since April 20. The bottom line (squares) is 2002 degree-days; the middle line (triangles) is the 11-year average (Sac City).  The top line (diamonds) is last year (2001).  As you can see in figure 3, we are running 100 degree-days less than normal, or 69%.  We have accumulated 195 fewer degree-days (59%) compared to the same period in 2001. 

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.

Sand storms in Iowa?
Last Wednesday was a rough day for emerged crops in area fields.  The high winds picked up sand and soil particles and moved them across fields, acting like a sand-blaster on corn plants.  Since the corn is so small, I would not expect any long term damage from the sand-blast injury.  Emerged soybeans could be a different story.  Sand-blasting can take out growing points on soybeans, ultimately killing the plant.  If you had beans emerged in a field that was blowing, you should go out and check it.  Pictures of the dust storm can be seen at:  http://extension.iastate.edu/carroll/crops/soil_erosion_wind.htm

Pest Management
Black Cutworm Trap Catch; Go to the following web page to see local BCW trap catch numbers http://extension.iastate.edu/carroll/crops/bcw_2002_trap_catch.htm  We should be scouting for cutworm activity now in area cornfields.  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.
 

Soil Fertility
If you plan to use the late spring nitrate test (LSNT) to determine the current N status of your corn fields, now is the time to start planning to take samples.  Samples should be taken when the corn is between 6 and 12 inches tall.  Refer to the ISU publication PM-1714 for more information.

The LSNT has been known too have accuracy problems.  Carrie Laboski (Michigan State University Crop & Soil Sciences) cited a north-central region study in the May 23 CAT Newsletter (http://www.msue.msu.edu/ipm/CAT02_fld/FC5-23-02.htm#8) stating that most errors in the PSNT (pre-side-dress nitrate test) lead to over-application of nitrogen.  If you have concerns that the test will tell you not to apply additional N when you really should, the study indicated that this only happened 3% of the time.  The total error rate was 30%.

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