By Mark Badertscher, OSU Extension Educator

Giant Ragweed and Marestail (horseweed) are problem weeds in some Hardin County soybean fields this fall.  A survey of 105 Hardin County soybean fields was conducted in September to determine which weeds are considered problem weeds in the county. 

There were also some fields with some volunteer corn, which had grown from the previous year’s crop.  This on-going research is conducted annually by OSU Extension to find out which weeds are competing with crops for nutrients and moisture, which decreases yields while increasing herbicide and other input costs.

The weed survey was conducted over a three day period, driving around the county and stopping at each intersection on a chosen route.  Weeds were scouted from the road in standing soybean fields with amounts being recorded as widespread, large patches, or occasional. 

After being recorded, these results are sent to OSU Weed Scientist Mark Loux for further analysis and statewide comparison.  The study will then be repeated yearly to find out the pattern of weed infestation around the county and state from year to year.  This information gives OSU Extension specialists better information for making weed control recommendations as some weeds are becoming resistant to certain herbicides that were once used to control them.  Although 68 fields were found to contain weeds, 37 fields were considered weed free.

Giant ragweed was found in 32 fields with 9 widespread, 4 large patches, and 19 occasional.  Marestail (horseweed) was found in 28 fields with 3 wide spread, 6 large patches, and 19 occasional.  Volunteer corn was found in 32 fields with 0 widespread, 4 large patches, and 28 occasional.  Other weeds occurring in smaller amounts were giant foxtail in 5 fields with 2 widespread, 1 large patch, and 2 occasional.  Pigweed was found in 4 fields with 1 widespread, 1 large patch, and 2 occasional.  Lambsquarter was found in 4 fields with 1 widespread, 2 large patches, and 1 occasional.  Cocklebur was found in 1 field, occurring occasionally.