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

[Home][Special Topics][Weather Data][Subsoil H20][PDF Info] [ISU Extension][IA State University]

Volume 5, Number 06
Northwest IA Crop Update, April 26, 2005
Print or view this newsletter in  PDF or Microsoft Word format.

In this issue

bullet Soil temperatures drop
bullet Corn emergence delayed
bullet Assessing corn emergence problems
bullet Calculate soybean seeding rate
bullet White grubs wanted
bullet Black cutworm moth catch

A rapid turnaround in air and soil temperatures has greatly slowed corn planting and emergence progress.  I estimate that approximately 15% of the corn ground in the area has been planted.   Corn planted as early as April 15 may not emerge until the first week of May.  Packing rains along with cold soils may lead to emergence problems, be sure to asses emergence progress and success on the early planted fields.  Degree-day accumulations for the next week will continue to be much below normal.  Now that May is quickly approaching, we are reaching the optimal time for Musk thistle control in pastures. 

Weather information
Soil Temperature Area soil temperatures followed the 3-year trend with a downward movement for five days before leveling off near 50 degrees F (Figure 1).  Nearly 13 degrees were lost in the cool down.  With a cool and cloudy week forecasted, I do not expect soil temperatures to warm much over the next five days.  Corn that is in the ground and not yet emerged will most likely not see much growth potential until soils begin to warm.  This is evident in the forecast emergence data in Table 2. Continue to monitor soil temperature at this web address:


Growing Degree Day accumulation is shown in Table 1 and Figure 2 and is forecasted through May 01.  Degree day accumulation through much of April has been much above normal (evident with the April 10 accumulation) but is now forecasted to be much below normal (21 DD over the next 7 days vs. the normal of 40 DD as shown in Table 1).  We typically would see about 5 degree-days per day, but will only see about 2 DD per day through the end of this week. Typically, corn will emerge with an accumulation of 110 to 140 degree-days (base 50). 

Table 1.  Degree-Day Weekly Accumulation
  2005 2004 2003 14-Yr Ave
April 18 - 24 61 39 15 33
Forcasted April 25 - 01 21 44 49 40


Crop Management
Corn planting progress as been relatively slow over the last two weeks, I would estimate that about 15% of the corn has been planted, with less than 1% emerged.  We are still well within the recommend planting period of April 20 – May 05 for reaching optimum yield potential.  As soils begin to dry, be sure not to get into the fields too early, side-wall compaction  of the seed furrow (from planting in wet soils) can cause a much greater problem with stand establishment and ultimate yield potential than a couple days delay in planting. 

Predicted Corn Emergence Dates   With the downturn in temperatures, emergence predictions have been greatly delayed*.  Note that corn plantings in mid-April may not emerge until the first week of May (or about 18 to 20 days from planting).   The current forecast on corn emergence is found in Table 2.  

Table 2.  Predicted corn emergence dates by planting date and location
Planting Date   Story Monona O'Brien Hancock   Average
April 10   22-Apr 23-Apr 22-Apr 22-Apr   22-Apr
April 15   03-May 03-May 04-May 05-May   03-May
April 20   10-May 10-May 11-May 12-May   10-May
April 25              
April 30              
May 5              
May 10              

*I mentioned in last week’s newsletter that I would be using a new model (hybridMaize) to make emergence predictions, I later found out that the new model uses 70 degree-days for emergence estimation, whereas we typically assume it takes 100 to 130 degree-days to emergence.  Hence the April 15 predictions made last week were quite early.  I have since reverted back to the model I was using last year while a modification is being made in the HybridMaize model.

Corn Emergence Problems will most likely be observed this year in some fields with the cool, wet and potentially crusted soil conditions.  Use information is last week’s newsletter and from the ISU Corn Planting Guide to make stand evaluations.  Also consider white grub, seed corn maggot, and wireworms as early stand reducing insects to be on the lookout for.  Problems from stand reducing insects are more common when cool weather slows crop growth.  The May 5 – 12 (2003) edition of the Ohio C.O.R.N newsletter has a good checklist to run through when evaluating emergence problems.  Access the C.O.R.N. newsletter at this web address:

True white grubs wanted. Dr. Marlin Rice will be evaluating the neonicotinoid corn seed treatments again this year. If you know of fields that have true white grubs, he would greatly appreciate the opportunity to dig up several hundred for his experiments. Best locations are near cottonwood or willow trees. Email Dr. Rice at  if you know of an infested field.

Soybean seeding rates:  Harvest stands of 110,000 and above produce similar soybean yields in IA. Studies have shown that field stand losses of 15 to 30 percent are common. These field losses are due to lack of seed germination, insect and disease damage, barren plants, lodging, and many other factors. Each field will likely have a different stand loss. Therefore, if a producer wants to harvest 130,000 plants and has a 23 percent stand loss before harvest, the seeding rate should be 159,900 seeds per acre. Adapted from “Soybean planting decisions ISU ICM newsletter 04/15/2002 (

Pest Management
Black cutworm (BCW) update. The pheromone traps have been placed across the state and there have been a couple nights that had large numbers of moths captured. The first time period was around April 10th and a second set was in the April 18-19th timeframe. Dr. Marlin Rice said that the recently received frosts will have “minimal effect” on egg viability and larvae survivability. At this point, plan to scout fields beginning May 15th and keep scouting them until corn reaches stage V4. (


Print or view this newsletter in  PDF or Microsoft Word format.

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

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This page last updated on 04/26/05

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