There is forage value in some weeds if they're grazed before heading out. But if they're allowed to go to seed, their weed seeds spread.
Despite two April snowstorms, rain and cold temperatures, Upper Midwestern pastures still have aftermath effects of last year’s drought to deal with. So says Mark Renz, University of Wisconsin Extension weed scientist.
He warns that, because of overgrazing last year, producers should expect slow pasture regrowth and, most likely, increased weeds this spring. That makes weed management in pastures crucial.
After identifying which plant species are germinating, develop a management plant based on weed density in your pastures, he tells growers. Any unknown plants should be identified in case they’re toxic or regulated invasive plants and then controlled immediately.
“We recommend removing animals from areas with highly toxic plants and controlling populations with the appropriate management at the correct stage of growth. This could be well into summer depending on the species,” he says.
If herbicides are used, keep animals off treated areas for at least 14 days. “Herbicides can increase the palatability of many poisonous plants,” Renz adds. That could increase intake and cause animal toxicity.
For plant identification information, as well as help in recognizing poisoning symptoms in livestock, download Common Poisonous Plants of Concern for Wisconsin’s Livestock.
Expect increased problems from Canada thistle and other perennial weedsthis year, he says. Canada thistle can “greatly reduce forage productivity and utilization of forage grasses. I suggest intensive scouting and management of Canada thistle and other perennial pasture weeds (e.g. horsenettle, hoary alyssum) to prevent spread.”
High populations of biennial weeds, including plumeless thistle, wild carrot (Queen Anne’s lace) and burdock, will also likely germinate this spring. “As biennials require a year of overwintering to flower, I don’t expect to see dramatically larger flowering populations until 2014; plants will be seedlings and rosettes in 2013.” Because it’s most effective, control these weeds at the rosette stage, he urges.
Anticipate more annual weeds, such as lambsquarter, ragweed and yellow foxtail, in pastures this spring, too. They start germinating from mid-April through June and could continue through August. See the weedometer for germination timings of specific weed species.
“Annual weeds are most problematic in continually grazed pastures, as they are rarely eaten in continuously grazed situations and deter animals from feeding on desirable forage growing among the weeds. Rotationally grazing your animals can alleviate many of the negative effects of these species if timed correctly,” Renz says.
If grazed before they flower, most broadleaf weeds offer good forage quality and can prevent seed production. Broadleaf herbicides also suppress the weeds. If the right chemical is chosen and applied at the right time, expect effective removal without harming established grasses. If there’s a desirable legume in the pasture, however, avoid broadcast spraying to keep from injuring it.
Yellow foxtail and other annual grasses will likely be a part of the mix. They, too, can be grazed before flowering, but their forage quality is low. “No herbicides are registered for use to control annual grasses in Wisconsin pastures, therefore the best approach to manage these plants is to prevent emergence and promote the growth and competitiveness of the desirable forage present,” Renz says. To control annual grasses and broadleaf weeds, leave a minimum of 6” of residual or actively growing forage plants – 8” inches are ideal – in the pasture. “This can be difficult to accomplish for some species as they can emerge throughout the entire growing season.”
Don’t be surprised to see a high number of clovers. Limited residual cover and reduced competition from existing forage give them room to grow.
“While many graziers add clover seed to pastures periodically, these legumes have a hard seed coat that allows them to survive in the soil for many years. So even if clover seed was not added for several years, there is a chance that clover will germinate and appear in your pasture,” Renz says.
Along with useful red clovers will come the unwanted legumes, including prostrate or feral white clover, he warns. “If desirable clovers are present, manage weeds and desirable forage so that they do not out-compete establishing clovers. This can be done with grazing or clipping/mowing. Typically, clovers readily establish as long as they get an opportunity to emerge and develop a root system. I expect the slow regrowth of pasture grasses and low residual cover will be enough for good establishment in most pastures.”
Don’t overgraze these areas, especially in spring, because that will reduce establishment. And don’t use broadcasted herbicides, which will injure or kill establishing clovers.
Several agronomic practices will also help diminish drought damage. Check out this 2013 Pasture Management Tips: After the Drought publication for information on assessing pasture condition, soil fertility, grazing management, and pasture renovation options.
For weed identification resources, visit:
For weed management help, check out:
• Pest Management In Wisconsin Field Crops, the Forages and Pasture weed management section, pages 182-191