May 10, 2011
It's amazing how much corn can be planted with a few good planting days. Many growers have now finished with planting corn, even though many didn't get started until a week ago. If the rains hold off another 2-3 days the majority of the corn should be planted in the area.
Hopefully the corn that got planted before mid April is spiking now with this hot weather. The long cold spell may have resulted in some stand losses on these fields, so stand evaluations should be made soon. Full yield potential can be achieved when the corn is planted by about May 5-10, although this varies from year to year. In most years we lose about 10-20% of the yield potential when planting is delayed until late May, so potential yields drop about 1-2% per day after about May 10. Potential yields drop off more rapidly if planting is delayed beyond late May.
Stands of 30,000+ will result in maximum yields. If stands are reduced to 25,000, count on a yield of about 95% of maximum. Corn stands of 20,000 results in yields of about 89% of maximum. This assumes that the remaining stand is fairly uniform. 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. The following table can help with re-plant decisions:
Influence of planting date and plant population on corn grain yields in Iowa
------------------ Corn Yields (% of maximum) -----------------
Stand April 20 - May 5 - May 15 - May 25 - June 5 -
X 1,000 May 5 May 15 May 25 June 5 June 15
35 100 96 87 70 54
30 99 95 86 69 53
25 95 91 83 67 51
20 89 85 77 63 48
15 81 78 71 57 44
10 71 68 62 50 38
This table comes from the latest Iowa research and modeling which is found on page 12 of the new Corn Field Guide (CSI001).
Numerous gaps of up to 4-6 feet can reduce yields by an additional 5-6%.
The usual method to check corn populations is to measure off 1/1000 of an acre in a row. That is 26'2 in 20 rows, 17'5 in 30 rows, 14'6 in 36 rows, and 13'9 in 38 rows.
For more information on checking corn stands, see the ICM article by Roger Elmore and Lori Abendroth at http://www.extension.iastate.edu/CropNews/2009/0514elmoreabendroth.htm.
Time to Scout for Black Cutworms
Cooperators monitoring black cutworm traps around the state have reported several peak moth flights in April. Because several flights have been recorded we have the potential for cutworm activity over an extended period of time. Just because the moths have arrived in Iowa doesn't mean we will have a big cutworm problem, but it does indicate when we need to start scouting for any cutting activity. The first peak flight occurred on April 6-9, indicating that cutting could begin around May 17 in SE Iowa (approximately south of I80), and May 19 in EC Iowa. The recent warm weather may change these predictions by a day or two. It is best to begin scouting a few days before the estimated cutting date, so scouting should begin this weekend. For more information on scouting for black cutworms see http://www.extension.iastate.edu/CropNews/2011/0505sisson.htm.
Many producers are finishing up with corn and switching to planting soybeans now. Even though optimum seeding rates have been increasing every year for corn, recommended seeding rates for soybeans have been going in the other direction. It's not that today's varieties perform better at lower populations, but that we have always over-seeded soybeans, partly because of concerns about weed control and because seed costs were relatively low. With today's better weed control and higher seed costs, it makes sense to seed at rates closer to what is really needed. This is one area where many producers can cut input costs without affecting the yield
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 soybeans 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.
FOR YOUR CALENDAR
IOWA LEARNING FARM COVER CROPS FIELD DAY
ROB STOUT FARM WASHINGTON COUNTY
2.5 MILES SOUTH OF WEST CHESTER
5:30 PM 7:30 PM
See and hear about Rob's and other area farmer's experiences with fall cover crops. More details soon.
SPRING FIELD DAY & SPECIAL SESSION FOR CCAs
SE IA RESEARCH FARM CRAWFORDSVILLE
The Spring Field Day of the Southeast Research and Demonstration Farm (Crawfordsville) will be on the afternoon of Thursday, June 15, 2011 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.
STRIP-TILL FIELD DAY
Doug Nolte and the Iowa Learning Farm (Iowa State University), hosts
1021 Highway 6, West Liberty, IA
JUNE 22, 2011, 10:30 a.m. Noon, followed by lunch
The farm is just in Muscatine County near the Johnson County line. Program details will be forthcoming.
NORTHEAST IOWA RESEARCH and DEMONSTRATION FARM, Nashua
SPRING FIELD DAY
JUNE 29 (tentative), 2011
Details will be posted soon at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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