By Amanda Douridas

Each year in late summer I drive a loop around the county noting types and severity of weeds I see above soybean canopies. OSU Extension educators and weed scientists have been conducting weed surveys around the state since 2006, which 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 means a moderate infestation with large patches and 3 indicates a severe infestation where there are multiple patches of weeds.

This year I travelled 90 miles, observing 3,365 estimated acres across 83 fields. The wetter growing season brought some unique challenges to weed management this year.

Volunteer corn has been on a bit of a roller coaster over the past few years. It was our most prevalent weed in in 2023 but declined sharply in ’24 and ’25 due to drought conditions. The rains this year once again helped it thrive and was found in 28% of fields surveyed, the second most prevalent weed.

I am sure you have noticed velvetleaf across many fields this year, which is another sign of a wetter year. Velvetleaf prefers damp soil, and it certainly thrived this year with it being found in 22% of fields. Previous years it was only found in a handful.

Waterhemp was and continues to be the biggest weed of concern for herbicide resistance. Also being a water-lover, it reared its ugly head across 1/3 of all fields surveyed. The concern is it has shown a tremendous ability to develop resistance across multiple herbicide groups in states to our west. The good news is that the average severity was just 1.26, meaning many fields only had a few weeds per field.

Each female waterhemp plant can produce thousands of seeds, so it does not take very long to build up a large seedbank. Harvest severely infected fields last to avoid spreading seed to other fields. Because waterhemp has a long period of emergence, residuals are a critical addition to herbicide plans.

I did find shattercane this year. While only in a couple of fields, it is concerning due to the challenges of controlling it in corn.

Other weeds I surveyed were relatively sparse with low densities. Redroot pigweed was found in 16% of fields and Giant ragweed in 13% (which continues its downward trend).

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. Make sure to apply pesticides when weeds are not in bloom 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 agcrops.osu.edu. Additional resources can be found at u.osu.edu/osuweeds.

Amanda Douridas is an Assistant Professor and the Agriculture and Natural Resources Educator for Ohio State University Extension in Madison County.