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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 22
Northwest IA Crop Update, August 22, 2005
Print or view this newsletter in  PDF or Microsoft Word format.

In this issue

bullet Corn for silage
bullet Predicting silage harvest dates
bullet Past the point of return on soybean aphids
bullet Soybean SDS
bullet Castana Field Day
bullet Crop update live

The ten-day forecasted warm temperatures should continue rapid crop progress toward maturity.  Preparations for silage harvest should be on the top of the list.  Grain harvest will not be far behind.  Soybeans continue to harbor some pests, spider mites, SDS, bean leaf beetles and even some Bacterial Pustule (Humboldt and Webster counties) can be found in area fields.  Soybean aphids can also be found, but most fields are most likely far enough along in development that a return to treatment will most likely not be seen.  If you haven’t yet attended a Crop Update Live session, be sure to attend this week’s program.

Weather information
Growing Degree Day  West-central IA continues to rack up the degree days with last week’s 145 DD accumulation, 14% greater than normal for the week.  This week’s forecasted accumulation (138) will also be above normal.  Notice the number for 2004, this was the first week of the early fall warming trend that occurred last year into September.  Accumulation and predicted plant phenology stages are shown in Table 1 and Figure 1 and is forecasted through August 28.  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
Aug 15-21 145 90 189 127
Forcasted Aug 22-28 138 142 174 131

Crop Management
Corn Development  Most corn in the area is denting with the milk line advancing down the kernel.  Corn harvest for silage will be occurring soon.  Information from a MN Extension newsletter ( suggests that corn requires 194 degree-days to advance from full dent to ½ milk line and 176 degree-days to advance from ½ milk line to black layer (physiological maturity). 


:   Predicting when to begin harvest can be a challenging task.  Corn silage that is too wet will yield less, will have silo seepage and will produce sour tasting silage resulting in lower intake by livestock.  If corn silage is too dry then yield is often reduced, heat damage and mold more easily develops in the silo because fermentation is inadequate, and the silage has lower protein and digestibility.  Harvest moisture also depends on the storage structure.

Table 2. Kernel milk stage "trigger" to begin sampling for various silage structures.

Silo Structure

Moisture content for Ensiling

Kernel Milk Stage “trigger”




Horizontal Bunker

70 – 65



70 to 60


Upright Concrete Stave

65 to 60


Upright Oxygen Limiting

60 to 50


*"trigger": kernel milk stage to begin checking silage moisture
*Silage moisture decreases at an average rate of 0.5% per day during September

Table 2 lists the recommended harvest moisture for different storage facilities.  Detailed information on harvesting corn for silage can be accessed at the following web site:

Corn Silage Harvest typically occurs between ¼ to ½ milk line, which under normal conditions will occur from 42 to 47 days post pollination.  According to projections based on the “Projected Phenology Events” table, plan silage harvest to begin from August 26 to September 05 based on silking dates of July 15 – 25.

Projected Phenology Events From Silk Date

Silk Date


1/2 Milk

Black Layer

Days from silk
















Pricing forage in the field?  Use this ISU Extension fact sheet found at this web URL:

Pest Management
Soybean Aphid
  Most soybean fields are most likely past the point (R5.5 to R6) of return to an insecticide application.  In the past, aphid populations tend to decrease or entirely disappear near the end of August.

Sudden Death Syndrome in soybeans has been found in central and north-central Iowa.  Early planted fields are at highest risk for infection.  X.B. Yang (ISU Extension Pathologist) describes symptoms as scattered yellow spots between leaf veins. These spots eventually coalesce to form brown streaks between the veins (interveinal necrosis). Only the mid vein and major lateral veins remain green. Leaflets drop eventually.  Diseased plants have deteriorated taproots and lateral roots. The root cortex is light gray to brown, and the discoloration may extend up into the stem 2 inches above ground. Sometimes bluish fungal colonies can be seen on the root if soil moisture is high.  SDS can spread rapidly throughout a field, detection and positive I.D. is essential to protect soybean yield and profitability.  Once a field has been identified with infection of SDS, select SDS tolerant varieties in subsequent years.  No resistance to this disease is available in any soybean varieties. 

Crop Update Live
Join me in the “Crop Update Live” web meeting to be held on Friday morning at 7:30 am.  I will review and update crop and pest management information presented in this week’s newsletter.  Click on this link  Friday morning to join the meting.  To view a recording of this or past meetings, browse to the Crop Update Live webpage

Fall Livestock and Crops Field Day
The Iowa State University Western Research and Demonstration Farm near Castana, IA will be hosting its annual fall livestock and crops field day on Thursday, August 25, from 1 – 3:30 pm.  Topics covered at the field day include:  Swine Welfare, Animal ID, Producers Role in Meat Quality, New Value Added Meat Cuts, What has happened with aphids and rust,  Solid Waste Settling March ’06 Compliance and Results of feeding Condensed Corn Distiller Soluables.  For more information contact the Monona County extension office at 712-423-2175


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

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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 08/23/05

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