Weed management in Ohio: Maybe we are getting better?

By Harold Watters, Ohio State University Extension

Our OSU Extension AgNR educators have been conducting fall weed surveys in Ohio soybean fields since 2006. That was about 10 years after the introduction of Roundup Ready soybeans and we were starting to see break throughs and wanted to document those occurrences.

We again observed soybean fields across the state this fall to see what was out there during our annual fall soybean weed survey. We each drive about 80 miles around our county and rank weed control on a 1 to 3 scale — with a 1 being very few weeds and a 3 a trashy mess. We also count the number of weed free fields.

Statewide our most frequently observed weed was again marestail as has been regularly since 2006 I believe. It was present in 21% of the fields. Giant ragweed is right there with it at 20%. Waterhemp is again a problem, even THE major problem, in some areas of the state. The count put us at 41% of the fields that were weed free, up significantly from last year’s 29%. Generally, for 2020 the county folks said, “Wow, it sure is clean out there.”

I also split the state into regions to see if maybe some were worse off than others. Some areas had other significant weeds, you will hear more about those when you attend your pesticide recertification training this winter or attend your regional agronomy day.

There were about 2,600 fields and 150,000 acres sampled to make these observations, enough that we have a good idea of what is happening in each region of the state. The OSU folks will report on local results and answer questions as we have our winter programs.

No area is without some resistant weed. However, pretty much all areas of the state had higher numbers of weed-free fields than they had last year. That’s good, but waterhemp and the pigweed species generally are looking a little scary in all of western Ohio. We know these guys are resistant to numerous herbicides already, and will likely become resistant to more. Mark Loux, OSU weed scientist, says mix it up and to rotate herbicide programs across all the packages that work — don’t rely on just one or you will be the one who Mark comes to visit to see just how you blew it.

This year we had the most counties surveyed — 30 — so the Ohio State University Extension educators are definitely working for you, and want to learn what is happening in your county.

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