By Harold Watters, Ohio State University Extension
I hear the neighbor’s combine running and the semi rolling past the house so it’s a good night to harvest late. Hopefully as everyone harvested their soybeans they were observing what weeds are out there. We did have an open canopy for an extended period into the year due to the cool, wet growing conditions. This often leads to an increased number of weeds. Our county educators have been observing soybean fields across the state this fall to see what is out there for our annual fall soybean weed survey. See table 1 for our results.
Table 1. The table below show the number of fields observed in each region, the percent of fields without weeds and weeds observed ranked by appearance.
|Region of Ohio||Number of fields observed||% of fields without weeds||Appearance by weed; ranked in order|
|Northeast||296||26||Marestail; grasses; Common lambsquarters; Volunteer corn; and pigweeds|
|East central||71||35||Marestail; Giant ragweed; Common ragweed; and Redroot pigweed|
|Central||206||45||Giant ragweed; Marestail|
|Northwest||755||46||Marestail; Giant ragweed; Common ragweed; grasses; pigweeds|
|West central||716||22||Giant ragweed; Marestail; Tall waterhemp; Volunteer corn; grasses|
|Southwest||270||33||Marestail; Giant ragweed; Volunteer corn; common ragweed; pigweeds|
We do have a number of fields across the state that are weed free – a rough estimate from these number is about one third. So that means that we can manage our weed problems in soybeans, but it takes paying attention and being a good manager.
No area is without some weed resistant to our major herbicide program – Roundup Ready technology. We have seen for a number of years now that Marestail is a major concern almost everywhere in the state. Few growers today can get away with ignoring this weed. Giant ragweed in some areas is now the dominant weed in soybean fields, and volunteer corn still is a problem – even though there are easy solutions for control of this lingering glyphosate tolerant volunteer. The pigweeds also appear in the surveys almost everywhere in the state – with a big appearance in west central Ohio. We must manage the pigweeds in general, and Waterhemp in particular much better than we do now.
So who conducts the Fall Soybean Weed Survey by driving 80 miles on the road in each county? In Table 2, is a listing of the counties in the survey, the Extension educator, the number of fields and the acres they checked on.
Table 2. County, educator, acres and field number by county in the 2017 Fall Soybean Weed Survey.
|County||OSU Extension AgNR educator||Acres surveyed||Total number fields|
|Coshocton & Muskingum||Emily Adams & Clifton Martin||3715||54|
That is over 2,000 soybean fields and 130,000 acres they sampled to make these observations. You can see in the list we had a significant number of counties and fields surveyed by our county Extension folks. Enough that we have a good idea of what is happening in each region of the state. They will report on local results by weed as we have our winter programs.
As I toured Ohio soybean growing areas over the summer, I checked with growers on what worked well for them. They reported the efforts they have gone to that reduced their weed problems in soybeans. Many found good yielding Liberty varieties and are happy they went all LibertyLink. And many of the OSU weed survey folks noted RRXtend signs on fields that had no weeds.
This is the list that works — and sounds an awful lot like the recommendations of Mark Loux our Ohio State University Weeds Specialist.
- Apply a fall burndown that includes 2,4-D.. plus dicamba, plus glyphosate, or whatever – just don’t spend the money now on a residual. Especially for Marestail control.
- Increase use of metribuzin. Always a residual in the spring, even on worked ground.
- A switch to LibertyLink varieties, and due diligence on these other suggestions.
- Use of full rate of pre-emergent herbicide at planting in the spring. Even on worked ground.
- I add number 5 for 2018. Consider dicamba resistant soybean varieties.
- But a couple of items have come up on this option – the formulations labeled for soybeans are now restricted use herbicides. Because we had some movement of this herbicide.
- This means you need to have a pesticide applicators license, and take continuing education classes on managing drift, volatility and the environment.
- And your likely target weeds – Marestail and Giant ragweed have already shown a great genetic capacity for evading control.
To learn more about managing weeds in Ohio. Attend your local county Ohio State University plant health recertification program – it was the Pesticide Recertification program but now includes fertilizer as part of the updates so I am calling it plant health recertification. Also recertification is now a four-hour program, up from three hours we had in the past.