Mike Hunter, North Country Regional Ag Team, Cornell University Cooperative Extension
We knew that it was only going to be a matter of time before we found herbicide resistant tall waterhemp and marestail in NNY. In July, we confirmed two fields on two different Jefferson County farms that have herbicide resistant marestail and three fields on one farm that has tall waterhemp seedlings.
Upon further investigation and doing some additional field testing we have strong evidence to believe that the two marestail populations are resistant to both Group 9 (glyphosate, i.e. Roundup) and Group 2 (ALS herbicides, i.e. Classic, FirstRate) herbicide Sites of Action. This finding is not surprising due to the fact that the seeds of marestail are windblown and can be easily moved 50 to 100 miles.
The tall waterhemp (see photo) was found in three adjacent fields on a farm in Jefferson County. Prior to this finding there were nine counties in NYS with confirmed populations of herbicide resistant tall waterhemp. While we cannot be sure that the tall waterhemp found in Jefferson County is resistant to any particular herbicide. We can certainly assume that it will be resistant to Group 9 herbicides based on the fact that all current populations of tall waterhemp in NY is known to be resistant to this herbicide family. We are currently working closely with this grower and will be doing additional testing to confirm its resistance to different herbicide families.
For additional information about marestail and tall waterhemp, I would encourage you to read an article on pages four and five of the CCE NCRAT North Country Ag Advisor May 2019 newsletter https://nydairyadmin.cce.cornell.edu/pdf/newsletter/pdf216_pdf.pdf
If you suspect you have one of these weeds on your farm or have a weed that is surviving applications of glyphosate please contact your local CCE Field Crop Specialist if you’re outside NNY or one of the CCE North Country Regional Field Crop Specialists Mike Hunter (315)788-8450 or Kitty O’Neil (315)854-1218. Don’t be afraid to bring this to our attention because we will keep farm name and field locations confidential.