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Smartweed in Pastures

Pennsylvania Smartweed

Have you ever noticed this weed in your pasture or hayfield? This is a smartweed and they are very common in wet areas like pond borders, ditches, hayfields, and pastures. Smartweeds are part of the polygonum genus which also includes knotweed, ladysthumb, curly dock, and red sorrel. There are annual and perennial smartweeds. The annual smartweeds emerge in early Spring and will grow throughout the Spring and Summer and dieback in the Fall. It is important to control these weeds before they go to seed because one plant can produce close to 20,000 seeds per plant. These seeds can stay dormant in the soil up to 10 years waiting for the right conditions. The wet winter and heavy spring rains this year have created prime conditions for these dormant seeds to germinate and could cause you to have a heavy crop of these weeds in your pasture this year.

Smartweed can be controlled by several post-emergent herbicides like Grazon Next HL, Metsulfuron, Chapparal, Milestone, and others. While 24-D by itself is doesn’t produce quite as good of control as some of these other products, mixing metsulfuron with 24-D is very effective. If you have a bahiagrass pasture, do not use metsulfuron as it will kill your grass.