Extension Crop Update Newsletter 7-16-18

Iowa State University Extension

View this email in your browser

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

July 16, 2018
Volume 21, Issue #9

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

Growing Conditions since May 1 – The following is a table I put together from the Iowa Mesonet, IEM Climodat Station Monitor website, with several NW and WC weather stations reports from so far this season. If you want to alter dates of information, go to the website, select the station you want, and alter the dates you wish to review.

As you already knew, we have had above average rainfall since May 1, and we have had higher than normal temperatures. In fact, on a day with a high of 85 and a low of 65, we would accumulate 25 growing degree days. So, since May 1 we are about 8 to 10 days ahead of normal. Although not shown in the table above, we are just a little ahead of normal for the accumulation of stress degree days. I heard a forecast saying the temperature will moderate some over the next 8-14 days. I believe that average to slightly below average temperatures after we pollinate are a good thing, so I hope it is correct!

Insects to Watch!
Soybean Aphids have been hard to find so far, but it is time to begin scouting. There are reports in southern Minnesota that the numbers are beginning to increase. As most know, I am not a fan of preventative treatments for this pest. Why spray for something that you cannot yet find? Remember, the treatment threshold is the 250/per plant on 80% of the plants, numbers we have mentioned for years – still plenty of time before they reach that 650 (economic loss level) number. Or for a scouting alternative, use the “speed scouting” method. To print off a copy of the speed scouting form, with directions, go here.

Corn Rootworms are finishing their time when they feed on roots and are emerging as adults. I still like to encourage producers to monitor the damage that might be occurring in your fields. Mid-July seems about the best time to dig and rate corn roots for the amount of damage present. The injury is quite fresh, and root regrowth that hides the damage won’t be as well established now. Check out this video from the University of Wisconsin on rating corn roots for rootworm injury.
This year we have several fields that have not pollinated yet due to late planting or excessive moisture, and we have emerging adult beetles. As these later pollinating cornfields begin to tassel be certain to get into these fields and scout for rootworm beetles that might be cutting the silks off, preventing pollination. A foliar insecticide may be warranted if there are five or more beetles per plant, silks have been clipped to less than ½ inch of the ear tip, and pollination is not complete.

Soybean Defoliating Insects – In July to early August we can often find species such as the bean leaf beetle, thistle caterpillar, soybean looper, green cloverworm, grape colaspis and likely some others who feed on the leaves of soybean plants. Some feeding can be tolerated, and after flowering begins the treatment threshold for each or a combination of all is 20% or more of all leaf area.The following picture is an example of what 20% defoliation on a single leaf looks like. Remember – the threshold isn’t for 20% on a single leaf, it is an average for the plant.

Third In-field Scouting Basics Session July 19 - Session 3 of this 3-part series will focus on scouting for insect during the mid-season. Corn rootworms, soybean aphids, leaf diseases and more will be discussed, in addition to a growth and development review. The Iowa State University (ISU) Northwest Research Farm located at 6320 500th St., Sutherland, and the session will run from 6:30 p.m. to 8:00 p.m. There is no charge to participate, but no food will be served, either. See additional details on the event flier. Don't worry if you couldn't attend the first two sessions!

Focus on Nitrogen Day at the NW Research Farm – August 21, 9:30 to noon. Topics to be covered include Nitrogen Application Management, including research on rate selection, split applications, time of application, N additives, manure N, and N in wet years. We will also do a review of progress towards the Nutrient Reduction Strategy N goals, what research is being done at the NW Research Farm, and look at edge of field practices to reduce N contribution to surface waters. Extension Field Agronomist Paul Kassel and I will lead the sessions. Register by e-mailing or sending me your intentions. There will be a $10 registration fee collected – but you need to register in advance (by Aug. 17) so I can plan for meals for participants at the conclusion of the event. To register, contact me via text (712-540-1085) or e-mail (jldejong@isatste.edu).

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

Nondiscrimination and Information Disclosures

My mailing address is:

Iowa State University Extension & Outreach

251 12th ST SE

Le Mars, IA 51031

Add us to your address book

unsubscribe from this list update subscription preferences