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Updated: October 25, 2017
At Ag Progress Days last week, one of the most common questions asked involved perennial weed control in grass hay and pasture. While we still have nice warm days, it is good time to scout pasture and hay fields for the presence of perennial weeds. As you hopefully have heard before, late summer and fall is the best time to control most perennials with a systemic herbicide because herbicides are moved into the root systems allowing more permanent control. With the autumn weather, these plants more actively transport carbohydrates and sugars to underground storage structures such as rhizomes, tubers, and roots to enable them to survive the winter and to provide the necessary energy to begin the next cycle of growth in the spring. Mowing the pasture and hay fields in mid-summer or several weeks before the herbicide application to prevent seed production and to promote healthy new leaf tissue that can intercept the herbicide is also important. In general, the application window runs from early September through October depending on where you are in the state and what weeds you are targeting. For the warmer season perennials like johnsongrass, horsenettle, groundcherry, wirestem muhly, Japanese knotweed and poison ivy, herbicide application between September 1 and 15 is generally ideal. For weeds like hemp dogbane and bindweed, make applications before October 1, and for quackgrass, other cool season grasses, and Canada thistle, try to make applications by October 15. These suggested dates target central PA, so adjust by a week or so forward or backward if you are south or north. Here is a list of the most common herbicides labeled for grass pasture and hay and some of their strengths/precautions.
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