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ISU Extension Logo

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 09
Northwest IA Crop Update, May 23, 2005
Print or view this newsletter in  PDF or Microsoft Word format.

In this issue

bullet Warmer forecast ahead
bullet Corn development at V2
bullet Soybeans emerging
bullet Alfalfa at PEAQ quality
bullet Soybean Rust 1st detector training
bullet Plan for LSNT

Scattered showers kept some out of the field last week, but warmer temperatures greatly aided crop emergence and development progress.  The extended weather forecast looks positive for more warm temperatures this week.  Corn development ranges from V1 to V3 in most fields, when corn development reaches V4 the yield potential is beginning to be developed.  Soybean planting is nearing completion; refer to table 2 for predicted emergence dates.  Alfalfa is in mid to late bud stage and harvest has begun for those looking to obtain high quality forage.   An initial training is being offered for those wanting to be soybean rust First Detectors, contact the Carroll Extension office for more details.  An update training is being offered at FEEL to those already trained as first detectors; refer to this website for more details. 

Weather information
Soil Temperature Area soil temperatures have continued to climb and now average in the mid to upper 60’s, ideal for soybean germination and emergence (Figure 1).  If the extended weather forecast holds true, soil temps should remain stable if not continue to warm. Continue to monitor soil temperature at this web address:

Growing Degree Day  Last week, N.W. Iowa picked up more than the average amount of degree days (92 vs. 72) which greatly aided crop emergence and development.  The seven day forecast also looks favorable with 89 degree-days predicted compared to the average of 82.  All planting dates (except for plantings during April 20 – 30th) are near normal in degree-day accumulations (Figure 2).  Accumulation and predicted plant phenology stages are shown in Table 1 and Figure 2 and is forecasted through May 29.  More detailed degree-day accumulations by planting date can be obtained at this URL:

Table 1.  Degree-Day Weekly Accumulation
  2005 2004 2003 14-Yr Ave
May 16-22 92 87 58 72
Forcasted May 23-29 89 75 80 82

Crop Management
Corn development
   Corn planted on or before May 10 should be emerged and corn planted during the cool April 20 – 30th time frame should be at the V2 stage and near V3 by next weekend.  Corn planted in early April should be at the V4 leaf stage.  The V4 stage begins the period 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.  Use the corn development chart (figure 2) to help predict timing of corn V stages.  If you want to figure you own crop development schedule, figure that corn requires about 75 degree-days (base 50) for each new leaf.  


Soybean Development  The majority of soybeans are now in the ground with the beans planted on May 10 emerging today (range 20th – 24th).  See table 2 for predicted emergence dates based on planting date for 4 locations in N.W. Iowa. Soybeans that have emerged range from VE to V1 (1 nodes).  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).
Table 2. Predicted soybean emergence Dates (model run on 5/23)
Planting Story Monona Hancock O'Brien N.W. Iowa
Date Ames Castana Kanawha Sutherland Average
30-Apr 16-May 13-May 18-May 18-May 17-May
05-May 16-May 15-May 19-May 19-May 17-May
10-May 22-May 20-May 24-May 22-May 22-May
15-May 27-May 24-May 28-May 26-May 26-May
20-May 30-May 27-May 31-May 29-May 29-May
25-May 04-Jun 02-Jun 04-Jun 04-Jun 04-Jun

Replant Decisions:  Obtain the Corn Planting Guide and the Soybean Replant Guide for help in making replant decisions.  Both can be obtained on the web or from your local ISU Extension office.

Alfalfa Management  Most alfalfa fields in N.W. Iowa are in the bud stage. The alfalfa height ranges from 19 inches to 27 inches.  May 23rd PEAQ results for NW Iowa showed Relative Feed Value (RFV) ranging from 172 to 207.  Fields are progressing slower than normal.  When fields enter in the 190 RFV range, then operators who want to harvest dairy quality forages need to watch weather and opportunities to harvest.  Each point of RFV is worth approximately $1 to dairy and livestock rations by way of reducing feed costs and improving intake, especially to lactating dairy cows.

Table 3.  Relative Feed Value


Height (in)





















Late Veg










*Relative Feed Value




Pest Management

(Initial) Soybean Rust First Detector Training. A training session for certified crop advisers and/or agronomists who want to be certified as an Asian soybean rust first detector will be held May 25th from 9:00 a.m. until noon at the Carroll County Extension Office in Carroll. A $20 registration fee will be collected at the door. Due to limited seating space, pre-registration is encouraged. For more information contact our office at 712-792-2364 or e-mail to Similar training sessions will be offered in other locations across the state, you may want to check with your local Extension Crop Specialist for the location nearest you.  (3 CCA CEU's (pest management) will be provided for certified crop advisers attending this class)
Soybean Rust First detectors. First detectors will be the first point of contact if a farmer suspects she/he has soybean rust in their field. It’s the role of the first detector to make the initial assessment of the disease in the field being inspected. First detectors have attended a training session to help them learn to diagnose Asian soybean rust and to diagnose other common soybean diseases that are often confused with soybean rust. 

Identifying, Confirming and Managing Asian Soybean Rust in Iowa (SP 257) and Common Soybean Leaf Diseases and Asian Soybean Rust (Pm 1989) are two Extension publications that discuss the ISU Extension FAST TRACK system.
First detector update training. All current ASR first detectors should have received a mailing from ISU Extension announcing three first detector update meetings on May 24, May 26, and June 1. These three meetings will all be held at FEEL near Ames.

Iowa Bee Rule.  If you are applying a pesticide that is hazardous to bees, you need to contact registered bee yards within a two mile radius of the field.  More information at

Soil Fertility
Nitrogen Management.  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.  PM 1714 can be access on the web at



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

For questions or comments please respond to

The information given in this publication is for educational purposes only.
Reference to commercial products is made with the understanding that no
discrimination is intended and no endorsement by Iowa State University with
any specific product(s) used in this is implied

This page last updated on 05/23/05

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