May 3, 2010
As corn emerges, stands are being evaluated. So far I have not encountered nor heard of any stand that isn’t “a keeper.” The most recent corn population study results are at http://www.extension.iastate.edu/CropNews/2009/0514elmoreabendroth.htm. 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 http://www.extension.iastate.edu/Publications/NCR344.pdf. There is also useful information on non-uniform emergence at http://www.agronext.iastate.edu/corn/production/management/early/height.html.
The weather may have 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 http://www.extension.iastate.edu/CropNews/2009/0519robertson.htm. I have received a few scattered reports of rots on coleoptiles (spikes) as corn is approaching emergence in some low areas of fields. So far, it appears the coleoptiles still have enough integrity that they should remain intact until emergence occurs.
The stalk borer egg hatch is well underway. In areas that had substantial populations of giant ragweed or grass in 2009, stalk borers may initially move into 2010 weeds that are present. When the weeds are killed, the stalk borers may then move into corn. Including a labeled insecticide with the post emergence herbicide may be helpful in this instance. Stalk borer activity is based on Growing Degree Days Base 41. Growing Degree Days Base 41 for Burlington, Davenport, Cedar Rapids, and Dubuque, as well as additional stalk borer management information, are posted at http://www.extension.iastate.edu/Pages/eccrops/stalkborer.html.
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 http://extension.agron.iastate.edu/soybean/documents/OptimumPlantPop.pdf for more information.
I have neither encountered nor heard of any issues with alfalfa
weevils this year, but be sure to scout for this pest in alfalfa fields. For
details on scouting for and managing alfalfa weevils, see the Integrated Crop
News article at http://www.extension.iastate.edu/CropNews/2009/041709pope.htm. Alfalfa weevil activity is based on
Growing Degree Days Base 48.
Growing Degree Days Base 48 for Burlington, Davenport, Cedar Rapids, and
Dubuque are posted at http://www.extension.iastate.edu/Pages/eccrops/alfalfaweevil.html.
The recent frequent rains may be promoting leaf and stem diseases of alfalfa. If severe disease levels occur, early harvest to avoid severe defoliation may be warranted. For scouting, identification, and management details, see X.B. Yang’s article at http://www.extension.iastate.edu/CropNews/2009/0506yang.htm.
FOR YOUR CALENDAR
SPRING FIELD DAY & SPECIAL SESSION FOR CCAs
SE IA RESEARCH FARM – CRAWFORDSVILLE
JUNE 24, 2010
The Spring Field Day of the Southeast Research and Demonstration Farm (Crawfordsville) will be on the afternoon of Thursday, June 24, 2010 at the farm. Certified Crop Advisor (CCA) credits will be available. In addition, Certified Crop Advisors can obtain additional hours of credit (including soil and water) by attending a special session in the morning followed by the afternoon tour. More details will be posted soon at http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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