Waterhemp Increasing in Hardin County

Written by on October 10, 2019

Hardin County – Each year before soybean harvest, county Agriculture and Natural Resources Extension Educators conduct a county weed survey. The purpose of this survey is to determine the type and amount of weeds that are infesting farm fields. Another reason is to develop an understanding of which weeds are becoming resistant to herbicides used by farmers. Once these determinations are made, weed scientists at The Ohio State University develop weed control programs which are then passed off to local county Extension Educators to make recommendations for local farmers. The goal of these recommendations is to help farmers gain control of these weeds so that their yield-limiting impact is reduced, increasing production and profitability for the farmer.

Hardin County’s weed survey was conducted October 2 in the southern part of the county. The route taken was east on State Route 309, circling around the southern part of the county, and returning from the west on State Route 67. October 4 the northern part of the county was surveyed, starting on State Route 67 going east. The route continued around the northern part of the county and returned from the west on County Road 106. Stops were made every mile at each crossroad, checking the soybean fields from the road. Data on the type of weeds found and the degree of infestations were documented. This information was then summarized on a spreadsheet that was sent to the University. Details from this survey will be used as part of the pesticide recertification training meetings January through March around the West Central Ohio Region.

A total of 102 fields were surveyed in Hardin County this fall. Giant ragweed was found to be a problem in 28% of these fields, tied with marestail (28%), then waterhemp (19%), volunteer corn (18%), giant foxtail/grasses (6%), common lambsquarter (5%), velvetleaf (1%), and redroot pigweed (1%). The highest degree of infestation in individual fields was giant ragweed, marestail, waterhemp, and volunteer corn. Thirty-three percent (33%) of the 102 soybean fields surveyed were found to be weed-free which was an improvement over 2018. This year’s increase of weed-free fields as compared to last year can be attributed to later planting of soybean or better use of weed control programs. Fields were evaluated as weed-free, occasional (occasional individual plants), large patches (patch of 8 or more plants scattered in field), or widespread (numerous patches or individual plants across the field) for each species in the field.

Waterhemp is a spreading weed problem across the county that farmers need to understand. Last year this weed was in 12% of soybean fields, and it has increased to 19% this year. Three years ago, waterhemp was in 4% of the county soybean fields checked. This weed is a concern because it produces a minimum of hundreds of thousands of seeds per plant, germinates throughout most of the season, and requires greater herbicide costs to properly manage. If farmers find waterhemp in a field, they really should be treating it like Palmer amaranth and do not allow seed to spread. Ideally, plants need to be prevented from producing seed with a comprehensive weed control program or pull escaped waterhemp plants before they produce seed.

Waterhemp plants now contain viable seed that can easily be spread across a field. Combines will spread this weed seed within a field or from field to field, so avoid patches during harvest or wait to harvest these fields last, thoroughly cleaning out the combine. Because the seeds are so small, it is difficult to remove all of them. Fields that have waterhemp infestations will require a strict pre-emergence and post-emergence program with additional residual herbicides during each application. Farmers will then need to rotate herbicide chemistries and modes of action yearly because of the extreme ability of this weed to become resistant to herbicides. If no action is taken in these infested areas, this weed will quickly take over a field, further increasing herbicide costs and limiting yield with the likelihood of spreading this weed to new fields.

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