In many parts of the transition zone, including Maryland and Virginia, February is when superintendents apply a nonselective herbicide like glyphosate to dormant bermudagrass to control Poa annua, ryegrass and other winter annual weeds. This is a common application and one that superintendents do every year without many issues.
That said, if you feel that you are not getting the fully anticipated results from the application, it could have something to do with your water source. Negatively charged molecules in glyphosate can bind with positively charged cations in hard water, significantly reducing efficacy.
A simple solution is to buffer hard water with ammonium sulfate. When added to hard water, ammonium sulfate breaks down into ammonium and sulfate. As the negatively charged sulfate binds with the positively charged cations in hard water, the water is conditioned, and herbicide efficacy is improved. The best way to determine how much ammonium sulfate is needed – or if it is needed at all – is to perform a water test.
I have heard rumblings from superintendents lately wondering if they are experiencing glyphosate resistance because they did not see the weed control they expected. While resistance could be the problem, do not dismiss hard water as a possible culprit too.
Northeast Region Agronomists:
Adam Moeller, director, Green Section Education – amoeller@usga.org
Darin Bevard, director, Championship Agronomy – dbevard@usga.org
Elliott Dowling, agronomist – edowling@usga.org
John Daniels, agronomist – jdaniels@usga.org