Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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April 16, 2015




For those who may not have their spring seeding of small grains done yet, potential yields decline for both oats and wheat about 10% per week for each week planting is delayed after April 15, and an additional 15% per week if planting is delayed beyond May 1.  See Chapter 4 of the Illinois Agronomy Handbook, beginning on the page numbered 44, for more details.





In general, try to complete seeding of cool season forage grasses and legumes before May 1 as seeding after May 1 increases the likelihood that seeds will germinate but less frequent rainfall will allow the soil to dry out before roots are deep enough to reach moist soil, killing the seedlings.





Alfalfa Weevil 


Alfalfa Weevil problems in eastern Iowa have been few in recent years, but it is still best to scout for them.  Iowa State University recommends that scouting for alfalfa weevil begin at 200 Growing Degree Days (GDD) (base 48, from Jan. 1) on south-facing slopes south of Interstate 80, and at 250 GDD on south-facing slopes north of Interstate 80.  The easiest way to scout for Alfalfa Weevil is to start with a sweep net just to survey a field.  If there are some alfalfa weevil in the net, then follow the proper scouting procedure in (in the paragraph above Table 1) to determine if the economic threshold is reached.    Alfalfa weevil quit feeding at about 900 GDD Base 48.  You can monitor GDD Base 48 progress at


Evaluating Alfalfa Stands


There do not appear to be widespread problems with winter-kill in alfalfa, but there will always be some winter-kill, especially on older stands, so stands should be evaluated beginning when they are about 3 inches tall.  Dr. Steve Barnhart, ISU Extension Forage Specialist Emeritus, posted basic information on stand evaluation of alfalfa and other forages at:; the article is four years old but is still appropriate.


A publication that helps assess root health is available at:    This publication also provides the other option for stand evaluation called the “Stem-Count Method”. This is actually a better evaluation method then for plant counts, but you have to wait for stands to reach 6 to 10 inches in height for the assessment to be reliable. An ideal stand has 55 or more stems per square foot. Consider replacing stands that are less than 40 stems per square foot.


The University of Wisconsin Extension hosts the “Team Forage” web site that provides comprehensive information on forage production including fact sheets, videos (link is lower left on home page), presentations, and more.  Two short videos of relevance at this time are:

1)  “How to Start a Good Alfalfa Stand

2)  “Alfalfa Stand Assessment: Is this stand good enough to keep?





Rye cover crops that will not be utilized as forage should be killed soon if the field will be planted to corn; in general a height of 6 inches is probably the best.  Waiting until it to gets taller can be problematic for a couple of reasons:   1) the more growth, the harder the rye is to kill, 2) the more growth, the more alleopathic compounds will be produced that could interfere with the following corn crop yield.  Additionally, because of the corn yield suppression concerns, it is usually recommended to not plant the field to corn for about 2 weeks after the rye has been terminated; the later the rye is terminated, the later the corn will be planted.

More information is available as part of the frequently asked questions in “Cover Crops: Frequently Asked Questions”


Some herbicides may reduce glyphosate efficacy when mixed with glyphosate; see “Terminating Cover Crops” by Bob Hartzler.  In this article, Bob also notes that night temperatures of less than 40 degrees may reduce glyphosate activity.





No-till Fields


Winter annual weeds, perennials, and some summer annual weeds are present in some no-till fields. As we progress through the spring, remember that larger broadleaf weeds may take more a the pint/A rate of 2,4-D.  Corn can be planted 7 days after a pint or less of 2,4-D but 14 days after more than a pint of 2,4-D, and soybeans can be planted 15 days after a pint or less of 2,4-D but 30 days after more than a pint of 2,4-D.


Glyphosate Resistant Waterhemp


We have been witnessing more and more fields with waterhemp that does not respond to glyphosate.  When finalizing herbicide decisions, be sure diverse waterhemp strategies are part of the plan.


Some soil applied products that are effective on waterhemp are shown in the table below.


Herbicide Group






Prowl, Treflan




Metribuzin (Sencor)


PPO Inhibitor

Kixor product (Sharpen, etc.)

Authority, Valor



Dual, Harness, Outlook, Warrant, Zidua, etc.

Dual, Intrro, Outlook, Warrant, Zidua, etc.


HPPD Inhibitor

Balance, Callisto, etc.


Some post-emergent herbicides that are effective on waterhemp are shown in the table below.


Herbicide Group





Plant Growth Regulator

2,4-D, Banvel, Clarity, Status, Yukon, etc.





PPO Inhibitor

Blazer, Cobra/Phoenix, Flexstar/Reflex/Rumble


HPPD Inhibitor

Callisto, Impact, etc.


Many pre-emergent herbicides are now also labelled to be applied post-emergence, which allows the product to be applied later in the season to extend residual activity.  In this instance, Bob Hartzler, suggests splitting the herbicide application, which is sometimes called “layer residuals.”   See “Two Apps Are Better Than One.”





In general, farmers have been patiently waiting for soils to warm up before planting corn.  It is important to wait until the soil temperatures are near 50 degrees and warming before starting to plant.  See “Corn planting: Consider soil temperature and date” by Roger Elmore and Lori Abendroth.  Soil temperatures can be found at  We still have several days left in the ideal planting time; see “Updated planting date recommendations for Iowa” by Roger Elmore and Lori Abendroth. 




Spring Field Day – Southeast Research and Demonstration Farm

1:00 p.m., Tuesday, June 23, 2015

Crawfordsville, IA

In addition, training for Certified Crop Advisors will be conducted, beginning at 9:00 a.m.


Details will appear at:


Spring Field Day – Muscatine Island Research and Demonstration Farm

5:30 p.m., Tuesday, June 23, 2015


Details will appear at:


Spring Field Day – Northeast Research and Demonstration Farm

1:00 p.m., Wednesday, June 24, 2015

Nashua, IA

Details will appear at:



Hay & Forage Expo

June 24 – 25, 2014

Cannon Falls, MN







If you have any questions, please feel free to contact the Iowa State University Extension Office.
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