Lebanon Crop Management Video

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05 May 2011

Late Spring Early Summer Corn and Soybean Decisions

Del Voight - Senior Extension Agent - Penn State Extension

5 May  2011
We are experiencing probably the most difficult spring and early summer in years. As we move into June growers, will be staggering after the alfalfa harvest and rush to get crops in the ground.  Today one  might find themselves still having to plant some corn and soybeans. Here are some considerations. 
Corn
Research suggests corn will begin decrease in yield after May 10 somewhere between 2-2.5 bu/day as the planting window narrows there will be some economic considerations that may be required to make rational decisions. These charts from the Agronomy Guide might come in handy.

Table 1.4-8. Estimated grain yields for various planting dates and population rates. Figures shown are most applicable to fields with less than 125 bushels per acre

Table 1.4-8. Estimated grain yields for various planting dates and population rates. Figures shown are most applicable to fields with less than 125 bushels per acre.
Planting datePlants/A at harvest
12,00014,00016,00018,00020,00022,50025,000
Optimum yield (percent)
April 2072788387909395
April 2575818690939698
May 1778388929598100
May 6788388929598100
May 1177838892959899
May 1675818690939698
May 2173788387919495
May 2669758084879092
May 3164707579828587
June 559646973778081
June 1052586367707375

Table 1.4-8B. Estimated grain yields for various planting dates and population rates

Table 1.4-8B. Estimated grain yields for various planting dates and population rates. Figures shown are most applicable to corn fields with yields greater than 175 bushels per acre.
Planting datePlants/A at harvest
10,00015,00020,00025,00030,00035,50040,000
Optimum yield (percent)
Source: University of Illinois
April 154687888959999
April 105770819197100100
April 20587181919710099
April 3058708089959796
May 955687786919391
May 1950637280858684
May 2944566573777875
June 835475663676764
This spread sheet will allow one to compare corn to soybean incomes. farmdocdaily: Planting Delays and Switching to Soybeans: A New FAST Spreadsheet

Corn which is heat dependent, growing degree days are important to determine if the crop has enough time to develop before a frost.  This chart details the latest planting dates based on a hybrid requiring 2600 heat units (110 days)to develop. As the season progresses short season hybrids may need to be reviewed and used as necessary. Follow this link for the full factsheet detailing this relationship of heat and growth.  http://cornandsoybeans.psu.edu/pdfs/latest_planting_dates_for_corn_hybrids_in_pennsylvania.pdf
 As the crop progresses it will be critical to assess the need for addition N using the Chlorophyll meter.  Be sure you do not sample fields with more than 15lbs of commercial N up front and that the corn is at least V6 to gain accurate measurements.  Any other applications would be strictly a pencil estimate of additional N needs.  With late planting one might find that there are few weeds to compete with the crop.  Our weed research indicates the need to control weeds by the time they are the size of a dollar bill or 6 inches in height.
Finally as he soil is much warmer the need for starter fertilizer dimishes and probably can be avoided this time of year. There still is a need to treat seed if pest history of the field requires.

Soybeans
Illinois Extension
Soybeans do not lose yield at such a dramatic rate as corn however there are issues with switching from corn to beans and also considerations in planting late soybeans.  . First off if any residual herbicides have been used the carryover can be an issue. Particularly for atrazine based products. ALS materials are another concern, however, there are STS varieties of soybeans that could work in that scenario.
Row Width is critical as planting date moves into summer.  Switch from wide rows of 15 inch or more to narrow rows 15 inch or less as the planting season progresses.  Our research would suggest narrow rows late planted will outyeild wide rows.  Increasing plant population is also a good management tactic particularly as we approach double crop plant timeing in late June. The beans are going to rapidly grow and move toward R1 as nights become shorter and the populations approaching 200,000 will ensure adequate pod numbers later. This is particularly true of mid to late June plantings. 
Iowa Extension Regional differences in response to planting date
When deciding to switch from corn to beans in June it appears that in our area mid May returns to Corn mimic Soybeans however, by the first week of June returns favor Soybeans. Other pest aspects will also change this summers activity. Many pests are based on heat as well and judging by the heat units many are behind so expect them to rise about 2 weeks or more later than normal.
Since this spring and early summer are so different than what we have experiences before it is difficult to generalize any recommendations. Growers will need to take in as many facts as possible and coupled with the forage supply requirements begin to make cropping decisions to maximize profits this year.

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