Ag news: Annual survey of weeds in Madison County fields

Marestail was once one of the most severe weeds in soybean fields as depicted above but surveys the past two years have shown a decline in prevalence as more farmers have implemented better control strategies.

(Posted Oct. 26, 2023)

By Amanda Douridas
Madison County Extension Educator, Agriculture and Natural Resources

Each year in late summer, I drive a loop around the county noting types and severity of weeds I see above soybean canopies. Ohio State University Extension educators and weed scientists have been conducting weed surveys around the state since 2006. This enables us to monitor weed population shifts and herbicide effectiveness.

I use a scale of 1 to 3 with 1 representing a low infestation with an occasional plant present, 2 representing a moderate infestation with large patches, and 3 representing a severe infestation where there are multiple patches of weeds.

This year, I traveled 134 miles observing an estimated 4,715 acres across 93 fields. Overall, fields were pretty similar to last year with 31 percent of fields completely weed-free. Severity was low across most fields, as well. Marestail, once our worst weed, continues its downward trend with presence in only 5 percent of fields and very low severity.

On the other hand, volunteer corn continues to be one of the worst weeds infesting 30 percent of fields, up from 22 percent in 2022. Giant ragweed was the second most prevalent weed, infesting 23 percent of fields which is about the same as last year. Waterhemp is currently the big weed of concern for herbicide resistance. It has shown a tremendous ability to develop resistance across multiple herbicide groups in states to our west. Presence in Madison County fields did increase from 13 percent to 17 percent this year and had a slightly higher average severity than weeds previously mentioned.

The weeds that typically have a higher average severity are foxtails and other grasses. While only identified in 9 percent of fields, the average severity was 1.63, 0.38 points higher than the next highest severity, which was waterhemp at 1.25. Again, these severities are averages based on the 1 to 3 ranking.

Volunteer corn has been one of the most prevalent weeds in soybean fields in recent years.

Other common weeds to note are velvetleaf, common lambsquarter, and redroot pigweed, each of which were found in 9 percent to 10 percent of fields.

The most obvious reason for good weed control is to reduce competition for nutrients, water, and space with our crops. Weeds can also provide habitat for harmful insects and diseases, making it easier for those pests to impact crop yield. Weeds should also be kept from blooming when pesticide applications are anticipated to avoid killing beneficial pollinators which can be sensitive to certain herbicides, insecticides, and fungicides.

For more information on weed control, subscribe to the C.O.R.N. newsletter and view past articles at Additional resources can be found at

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