Crop Update Newsletter 5-11-18

Iowa State University Extension

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Extension Crop Update
This newsletter, and previous issues from recent years, can be found on-line at:
http://www.extension.iastate.edu/plymouth/info/cropupdate.htm

May 11, 2018
Volume 21, Issue #4

Prepared by
Joel DeJong,
Extension Field Agronomist
Click on photo for contact info

Corn Planting Dates – We all know that this has been a challenging planting season so far. I recognize that planting progress in the southern part of the region I cover has gone quite well, and many fields have emerged corn in them. As I move north and east in the region I am assigned I know many have planted only a small percentage of the acres of corn they would like to have in the ground by now. So, what does that mean? If it dries and we get a chance soon, we have only limited the potential a little – and if we get the right weather, maybe almost none. Here is a table from the ISU publication titled “Hail on Corn in Iowa,” which shows a summary of multiple years of planting date studies:

If you would like to see some of the studies that go into this recommendation, take a look at the NW Research Farm Summary on this work from 2014 – 2016 which can be found here. Other studies, years and sites are also used to generate the table above. You can see that as we near the end of May the yield expectation lowers a little more rapidly over time. Mark Licht, ISU Extension Cropping Systems Specialist, noted that the work from recent years showed a little higher yield in later May than this table would indicate.
What about hybrid selection? Mark’s data have shown that the best hybrids still gave the highest yields even late in May. We know that when corn hybrids are planted late they do adjust to that by shortening the time to maturity, as this ICM News article from 2007 discusses. Staying in the normally adapted hybrid range is probably a good idea through much of May, although you might want to stay away from those at the long end of the adapted range of hybrids for your area. Of course, the risk of wetter corn at the end of the season does increase with later planting, so how rapidly you change to the short end of your adapted maturity range might be different depending on your grain handling equipment available. An additional tool for evaluating maturity at different planting dates is the U2U “Corn Growing Degree Calculator” which is now hosted on the Midwest Regional Climate Center web site. Choose your county, put in your planting dates and corn maturity days, maybe select some comparison years, and see how development might occur under different scenarios. Note – I do not think this model adjusts for a late planting date as discussed in the article linked above.

Black cutworms? If you remember, black cutworms cannot live through an Iowa winter. So, ISU and other states have a volunteer trapping network in the spring that monitors when the adult black cutworms are arriving in Iowa. During the last couple of days in April and the first few in May, when those storms were rolling through, one NW Iowa trap and a few in SW Minnesota did catch significant numbers of adult cutworms. We will use the dates of trapping, and watch growing degree accumulations as we move through May to let you know when these larvae might be big enough to start cutting corn. Likely, about the end of the month, but I will update you with better recommendations in the next newsletter.

Alfalfa Harvest Time Approaches? – Last year at this time alfalfa fields near Le Mars were measuring 24” tall. Using the Predictive Equation for Alfalfa Quality (PEAQ) found here, that alfalfa would have a Relative Feed Value (RFV) of 190. It will be a while before we have alfalfa that tall here, but I wanted to let you know we will again be monitoring its growth and development this spring to aid in helping you time your alfalfa harvest for desired quality. Using the plant height and stage of growth is a good predictor of feed value, but you do need to make some adjustments for harvest.
Making haylage reduces the final RFV by 15 units, or making dry hay would cost about 25 RFV units. In general, it is recommended to harvest alfalfa at about 150 RFV for milking dairy herds and 125 RFV for heifers, stocker cattle and lactating beef cattle. First crop alfalfa standing in the field can drop 3 to 5 points of RFV per day. A one-week delay of first crop harvest could cost at least 20 RFV points in feed quality. I will check these fields every 3 or 4 days to monitor progress. Results are found on this web page, but monitoring your own field is more accurate!

Crop Scouting Basics - is a multi-session workshop being offered to anyone who is interested in hands-on learning about crop monitoring. This series of workshops will be held on June 7, 21, and July 19 at the Iowa State University (ISU) Northwest Research Farm located at 6320 500th St., Sutherland, from 6:30 p.m. to 8:00 p.m. each evening. The focus of this first session will be on crop development and staging to find what is ‘normal’ in order to help identify what is ‘not normal’, in addition to other timely issues of concern to participants. Weather permitting; the majority of the time will be spent out in the field with hands-on learning and experiences. There is no charge to participate in each session, but no food will be served, either. See the event flier here, and register by e-mail to jldejong@iastate.edu if you plan to attend. Registering helps me plan for reference materials for participants.

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Serving Cherokee, Ida, Lyon, Monona, O'Brien, Osceola, Plymouth, Sioux
and Woodbury Counties.

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