I completed the Fall Soybean Weed Survey in Darke County with the assistance of Weed Scientist, Dr. Jeff Stachler, Darke County native and Auglaize County Extension Educator.
The good news is that we have several parts of the county where growers are managing their resistant weed problems. The assumption is that most of Ohio soybeans are RoundupReady, and that if weeds are still in the soybean field at the end of the season, then there must have been a failure of the system — not always correct but then we are making assumptions that may not be too far off.
The Fall Soybean Weed Survey is completed by Extension Agriculture Educators across the state to evaluate weed pressure and to determine the levels of resistance that has been built in the different regions of the state. Each educator is asked to drive an 80-mile loop around their county and to evaluate the soybean fields at one-mile increments.
We drove an 89-mile loop and evaluated 91 soybean fields for all weed species. Because of the concern for resistant waterhemp showing up in Western Ohio, we looked at all 309 fields in the loop to determine if there was waterhemp in the field.
We found only 12 percent of the 91 fields completely void of weeds and volunteer corn compared to about 40 percent the previous two years. An occasional weed or corn plant could be found in another 15 percent of the fields.
So what species of weeds did we find in Darke County? The weeds include: Voluntary corn, 48 percent; Giant Ragweed, 43 percent; Marestail, 41 percent; Waterhemp, 25 percent; Velvetleaf, 22 percent; Common Lambsquarter, 19 percent; Giant foxtail/grass, 19 percent; Smooth pigweed, 9 percent; Morning glory, 8 percent; Pokeweed, 2 percent; Common Ragweed, 1 percent; Honeyvine Milkweed, 1 percent; and Redroot Pigweed, none.
So what is my takeaway from the tour of Darke County last Friday? Dr. Stachler and I spent a lot of time talking about that very question while we were finishing up. Our conclusions are:
- First, Mother Nature was not friendly to weed management in 2016.
- We probably have seven species of weeds in Darke County that are at least partially resistant to glyphosate.
- We have some growers that are very successful in their weed management.
- Tillage alone, which was once thought to be a great way to control marestail, is not working anymore.
- Waterhemp. Not much different than the dreaded Palmer Amaranth, is a severe problem. We found waterhemp in 66 of the 309 total fields we drove by in the 89-mile loop. Our estimate is that 44 percent of the fields in the north and western part of the county are infested.
What action needs to be taken?
1. Scout your fields for waterhemp now. If you have a few plants, pull them out carefully and place them in a bag and incinerate them. Do not run them thru the combine. Each plant has over a million seeds that you will quickly spread across the field and in to other fields.
2. Attend our pesticide meetings this winter. Mark your calendar today for February 7 to hear from weed scientists Dr. Mark Loux and Dr. Jeff Stachler give their recommendations for getting waterhemp off your farm or to prevent it from entering your farm.
3. Determine whether your waterhemp population is resistant to glyphosate and/or site 14 herbicides. Fortunately, there is a painless way to do this, through a service offered by the University of Illinois Plant Clinic. Link to the U of I newsletter article that provides the needed info: http://bulletin.ipm.illinois.edu/?p=3619.
4. The LibertyLink soybean system is, of course, another option for management of waterhemp, as well as Xtend and Enlist soybean systems whenever they become available.
5. It should be noted that: a) use of glufosinate, dicamba, or 2,4-D to help manage this weed does not change the approach, and these herbicides must be applied to small plants to control waterhemp; and b) the assumption is that inappropriate and continued use of these herbicides would lead to the development of resistance to them. And in fact there are already some populations of waterhemp farther west with resistance to 2,4-D.
Custer is the Agriculture and Natural Resources Extension Educator for the Darke County OSU Extension office. He may be reached at email@example.com Viewpoints expressed in the article are the work of the author. The Daily Advocate does not endorse these viewpoints or the independent activities of the author.
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