Iowa State University Extension and Outreach

East-Central and Southeast Iowa Crop Information


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May 20, 2009


Stand Evaluations

Corn stands have been and are being evaluated.  The cool weather and, in some locations, crusting have taken a toll, but so far I have heard of only one stand that isn’t “a keeper.”  The most recent corn population study results are at  The cost of re-planting and yield loss from late planting needs to be compared to any yield loss from stand losses to make a good decision.


Numerous gaps of up to 4-6 feet can reduce yields by an additional 5-6%.  For more information on the effect of gaps, see NCR 344 “Uneven Emergence in Corn” at  There is also useful information on non-uniform emergence at


The cool weather has also promoted seedling blights in some fields, so be sure to dig up a few plants to evaluate their health below ground.  More information is available at




Black cutworms should begin cutting soon if eggs were laid during the late April black cutworm moth flight.  Based on temperatures since then and using National Weather Service forecasts through May 26 and normal temperatures thereafter, cutting in eastern Iowa should begin along Highway 34 on Sunday, May 24, along Interstate 80 on Monday, May 25, along Highway 30 on Thursday, May 28, and along Highway 20 on Saturday, May 30.  It is always good to start scouting a few days before the predicted onset of cutting.  And, of course, any changes in predicted temperatures may alter the onset of any cutting.  You can monitor black cutworm growing degree days for east-central and southeast Iowa at   A more comprehensive overview of the 2009 black cutworm situation will be posted soon at the Integrated Crop Management News web site





Plant Populations


Even though optimum seeding rates have been increasing every year for corn, recommended seeding rates for soybeans have been going in the other direction. Recent work by Palle Pedersen has shown that the optimum final stand for soybeans is 100,000 plants per acre. Optimum seeding rates will vary depending on the seeding method used and germination of the seed, but it will seldom pay to seed at higher than 125,000-140,000 seeds per acre. Because of soybean’s ability to compensate for lower stands by branching out and producing more pods/plant and more seeds/pod, yields do not decrease much until populations get below 75,000 plants/acre. See Palle’s fact sheet “Optimum Plant Population in Iowa” at for more information.


Seed Treatments?


As we get later into May with warmer soil temperatures, it becomes less likely that fungicide seed treatments for soybeans will pay off. Insecticide seed treatments do a nice job of controlling overwintering bean leaf beetles, but they are a greater problem with the early planted soybeans which are already in the ground. The cold winter should also reduce our bean leaf beetle populations. See Erin Hodgson & Rich Pope’s article at Insecticide seed treatments are not very effective for controlling soybean aphids, because the treatment does not last long enough for killing aphids in August.


Soybean seed inoculants have been advertized a lot lately. Although the nitrogen-fixing bacteria are important for soybeans, it seldom pays to inoculate seed where soybeans are being planted in soils where soybeans have grown in the last 3-5 years. Palle Pedersen has had many trials out in Iowa and has yet to see a yield response to inoculating seed  in a corn-soybean rotation. See his article at One situation where an inoculant might pay off this year is in fields that were flooded for more than a week last year, which could have reduced the rhizobia bacteria population.



Incentives for Organic Agriculture


There is money available for farmers that are interested in transitioning to organic agriculture. Up to $20,000 per year is available from a new program in EQIP called “organic conversion assistance.” The deadline for signing up at the NRCS offices is May 29. See Kathleen Delate’s article in the ICM News for more information at









Certified Crop Advisors can obtain 5 hours of credit (including 3.5 hours in soil and water management) by attending a cover crop and residue management session in the morning followed by the afternoon tour at the ISU SE Iowa Research & Demonstration Farm near Crawfordsville on June 24. More details will be posted soon at


If you have any questions, please feel free to contact the Iowa State University Extension Office.
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Last Update: May 20, 2009
Contact: Virgil Schmitt

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