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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 22, 2018
Volume 21, Issue #5
Prepared by
Joel DeJong,
Extension Field Agronomist
Click on photo for contact info
Soybean Date of Planting: The last USDA Weekly Crop Progress report showed improvement, but it still wasn’t very kind for the northern edge of Iowa. In the last issue of this newsletter I discussed late planting of corn. Soybeans will be the topic for this issue. Here is a chart from ISU’s “Soybean Replant Decisions” publication that summarizes multiple studies on soybean maturity and planting dates. 
     Research results show that changing soybean varieties is not needed through the month of June. Soybeans typically reach maturity in mid to late September regardless of planting date. Soybean physiological maturity is minimally delayed by either planting date (5- to 10-day delay) or maturity group selection (up to 5-day delay). This minimizes the need to change soybean maturity group selection when faced with late planting situations.
     If you would like to see the data summarized in the NW and Northern Research Farm reports from a three-year project completed in 2016, click here for the NW Research Farm Report, and here for the Northern report. Note that in some years the yield difference between early and late planting dates is quite wide, while in others the difference is rather narrow. The table above gives averages, but the later the planting date, the wider the range around the average seems to be over time.
     As we know, crop insurance plays a large role in our decisions for late planting and replanting. An article titled  “Delayed and Prevented Planting Provisions for Multiple Peril Crop Insurance” was published on the Ag Decision Maker website during April that might be of help understanding that issue, also. If making changes, talk with your own agent about options.

Black Cutworm: Each year several traps for migrating adult Black Cutworms are placed across Iowa. Since they do not overwinter in Iowa, we trap these adults and use this information with growing degree day data to predict when they lay eggs, hatch, and get big enough to cut off corn plants. Moth catches from this spring have allowed ISU to make predictions of when you need to start scouting emerged corn plants for potential cutting.  That date is May 24 for NW Iowa, and May 22 for WC Iowa. I would encourage you to scout emerged corn, and keep an eye on areas that have been grassy, are low-lying, and have a history of BCW problems. These areas are favored for egg laying. If you have emerged corn along the western edge of the state you might want to start watching for problems soon! For more BCW scouting advice, check out this ISU ICM Newsletter article titled “Black Cutworm Scouting Advisory 2018.” In addition, we sometimes see other larvae out there that are not cutting plants, but maybe just feeding on leaves. Here is an older article from Illinois titled “Correct Identification of Cutworm Species Is Important Each Spring” that helps you tell the difference.

Alfalfa Harvest Time Approaches - Yesterday morning I was out in a couple of alfalfa fields near Le Mars. The fields had 24” tall alfalfa on average, and buds were not yet visible.  Using the PEAQ quality assessment model found here, that alfalfa would have a Relative Feed Value of 190. 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. Results from other counties can be found on this web page.

In-field Crop Scouting Basics Workshops Set - This hands-on series of workshops for anyone wanting to learn more about the basics of crop scouting 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 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 additional details on the event flier here, and please register by e-mail to jldejong@iastate.edu or call/text at 712-540-1085 if you plan to attend. Registering helps me plan for reference materials for participants.

Free White Mold Prediction App – Sporecaster, the white mold forecaster, is a new smart phone app created at the University of Wisconsin. As their newsletter article about the app says, “The best time to manage white mold is during flowering (R1 and R2 growth stages) when apothecia (small, mushroom-like structures) are present on the soil surface. Apothecia release spores which infect senescing soybean flowers, leading to the development of white mold. University research has indicated that the appearance of apothecia can be predicted using several variables including weather and amount of soybean row closure in a field. Based on this research, Sporecaster models have been developed to forecast the risk of apothecia being present in a soybean field.” ISU Extension Plant Pathologist Daren Mueller says they have validated it a bit in Iowa, and will continue to test it more over time. Download Sporecaster from the Apple or Google Play store. You can also watch a YouTube tutorial video.

 
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Serving Cherokee, Ida, Lyon, Monona, O'Brien, Osceola, Plymouth, Sioux
and Woodbury Counties.
My mailing address is:
Iowa State University Extension & Outreach
251 12th ST SE
Le Mars, IA 51031

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