May 16, 2012
There have been some losses in corn stand, especially with corn planted around April 23-27. After an unusual warm spell in March and early April, soil temperatures dropped back below 50F for several days in late April, which may have resulted in some inbibitional chilling and disease issues. Roger Elmore has a good article discussing the stand problems, which includes a picture of corn seedling growth problems from cold soils at http://www.extension.iastate.edu/CropNews/2012/0511elmore.htm.
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 262 in 20 rows, 175 in 30 rows, 146 in 36 rows, and 139 in 38 rows.
Time to Scout for Black Cutworms
The unusual weather this spring has made it harder to predict when cutworms will start becoming an issue because some early moth flights may have been missed and the frost in April may or may not have taken care of some of the early cutworms. Some cutting has already been reported along and south of I-80. Cutworms are a sporadic problem and not likely to be an issue in most fields, but fields should be scouted until they reach the V5 growth stage so they can be treated if needed. A general rule of thumb is to treat if you find 2-3% of the plants cut and the worms are less than ¾ inch long. However, higher corn prices may alter that rule. An Excel decision-aid and more information are at http://www.extension.iastate.edu/CropNews/2012/0425sissonjessehodgson.htm.
CORN AND SOYBEAN SEEDLING DISEASES
Alison Robertson, ISU Plant Pathologist, is looking for some samples from such fields. She will collect 50 seedlings from the field and take them back to Ames for laboratory analysis. If you have such a field and would be willing to give up 50 diseased plants from the field, please let me know and I will relay the specifics of the field to Alison.
FOR YOUR CALENDAR
SOUTHEAST IOWA RESEARCH and DEMONSTRATION FARM, Crawfordsville
SPRING FIELD DAY and 25th Anniversary Celebration (afternoon) &
SPECIAL SESSION FOR CCAs (morning)
JUNE 21, 2012
Details will be posted at http://www.extension.iastate.edu/Pages/eccrops/meetserc.html.
NORTHEAST IOWA RESEARCH and DEMONSTRATION FARM, Nashua
SPRING FIELD DAY
JUNE 28, 2012, 1 4:30 p.m.
Details are posted at http://www.extension.iastate.edu/Pages/eccrops/meetnerf.html.
TECHNIQUES and TECHNOLOGIES TO AVOID SPRAY DRIFT
July 17, 2012, Field Extension Education Laboratory (FEEL) near Boone, IA
Two half-day sessions (morning session repeated in the afternoon) (no cost to participants) will be conducted, focusing on:
- Nozzle selection/use with demonstration on spray table
- Balancing efficacy and drift
- Environmental factors, adjuvants and limitations, field demonstration, etc.
More information and registration will soon be available at http://www.aep.iastate.edu/.
If you have any questions, please feel free to contact the Iowa State University Extension Office.
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