When it comes to controlling weeds in horse pastures, identifying the type and knowing how to combat it are key to success. You must take control measures at the appropriate time in the plant’s growth cycle. Otherwise, you’re wasting time, effort, and money.
Andy Kness, MSc, agriculture educator for Harford County, Maryland, described common weed categories (particularly in the mid-Atlantic region) and how to manage them during the University of Maryland Extension’s healthy horse-keeping webinar series.
Winter annuals germinate in the fall, overwinter (go dormant), then flower the following spring, dropping seed and repeating the cycle. You can best control them by mowing before they set hard seed in the spring. Apply chemical controls (e.g., herbicides) in fall or early spring.
Common winter annuals species include pennycress, shepherd’s purse, purple deadnettle, henbit, and mustards.
Summer annuals are heat-loving species that germinate in late spring (mid-April through May, when soil temperatures reach the 50s, said Kness) and flower and seed in midsummer to early fall. Mow to control these species before they set hard seed in the summer and fall. Apply chemical controls in late spring to early summer.
“Pre-emergent controls (that you must apply before weed seeds germinate) can be very effective,” Kness said.
Common broadleaf summer annuals include pigweed, spiny amaranth, jimsonweed, and nightshade. Common grass summer annuals include foxtail, crabgrass, and Japanese stiltgrass.
Perennials persist year to year from their roots and stems. They go dormant in the winter, but return in spring, said Kness. Control perennials using repeated stressing (e.g., grazing, mowing, spraying with herbicides). Chemical control is most effective just prior to flowering or when plants are still small, he said.
Perennials “can take a long time to control,” said Kness. “It might take several years and growing seasons.”
Common perennials include Canada thistle, buttercup, milkweed, dogbane, chicory, dandelion, dock, horsenettle, and plantain.
This weed type is in between annual and perennial—it lives for two seasons and dies, said Kness. Biennials germinate from seed and grow in a rosette one year, then bolt (grow rapidly) and flower the next year. Control these weeds by mowing before they form hard seed in their second year, he said. Apply chemical control in the late fall or early spring while the weeds are still in their vegetative state (rosette form).
Bull thistle is an example of a common biennial.
Walk your pastures regularly and at different times of year to identify weed types. Then target your control methods to the problem species you encounter. Your local extension office or ag agent can help you identify pasture weeds and come up with the most effective pasture management program for your property.