by Deborah Jeanne Sergeant

Want to save money on forage? Pasturing is the least expensive way to feed the herd; however, if a pasture is not well-managed, that decreases the pasture’s productivity. Dr. Mark Renz, University of Wisconsin Madison Extension weed specialist, presented “Pasture Weed Management” as a recent webinar.

“Pastures are a unique system,” Renz said. “It’s not considered a high input system but there are complex decisions to be made. You can’t manage pastures like a corn or soybean field. There are complex processes.”

He said that weeds are important, but farmers need to decide at what level they will manage them. “We need to optimize their performance to optimize the performance of the animals,” he said.

Farmers need to identify their weeds, monitor them, as some are not problematic, and manage the problematic ones through changing growing practices, fertilizing/renovating pastures, mowing and applying herbicides.

Renz said weeds in a pasture need to be controlled if they reduce desirable forage quantity and quality; reduce plant palatability and utilization; and reduce animal health and/or performance. But weeds rarely reduce the total forage available.

“The biomass can be significant of our weed species,” Renz said. “Sometimes the management, while it gets rid of the weed species, can also impact other components – clover in particular.”

While spraying may get rid of dandelions, it does not benefit the desired forage. The presence of dandelions does not deter livestock from grazing, so spraying for that weed does not benefit the pasture.

“Make sure the extra utilization of grasses makes up for the loss of biomass,” Renz said.

He also said weeds can be considered forage in some cases. “Think of how much of the weeds are eaten by animals,” he said. “We’ve gotten animals to even eat spiny weeds, up to three-quarters of a ton per acre of biomass. It can be significant.”

Some weeds can even offer good forage quality. Renz cited Neil Martin, formerly of the USDA-ARS Dairy Forage Research Center: “Canada thistle has forage quality that is equal or superior to alfalfa.”

Jerry Doll, emeritus weed scientist with UW-Madison, stated, “As long as alfalfa fields are well managed, dandelions will not cause any decline in forage yield or quality.”

Renz said annual broadleaf weeds have moderate to high forage quality, which is highest when vegetative. “Quality declines rapidly as they mature,” he added.

Annual grasses have lower quality forage with less protein and more fiber. Common perennial broadleaf weeds, like dandelion, plantain and white cockle, have high forage quality. Doll said these are equivalent to desirable forage species.

Spiny weeds are reported to cause up to 72% of reduced palatability/utilization, depending upon the developmental stage of the weed species. More mature plants are less palatable. “If we have spiny weeds … we can get reduction in utilization, not just in the weeds but in the plants nearby,” Renz said. “The animals don’t want to get close to that spiny material. The more vegetative, the more we get results.”

The grazing method makes a difference too. In continual systems, these weeds are almost completely avoided. “If it’s rotational, we can get high levels of utilization with a high level of stocking,” Renz said. “They lose that selection pressure.”

While high density stocking sounds like an easy way to get animals to eat less desirable plants, Renz offered a caveat: “If you have poisonous or toxic plants, like milkweed, they may well be ingested because of the change in behavior in those animals.”

Thankfully, poisonous plants are generally not palatable, so animals usually avoid them. Renz also said toxicity depends upon how much of the plant is ingested. Sometimes, animals will develop a tolerance for toxic plants, so it’s important to scout pastures and know plant species. Renz listed common causes of poisoning: early grazing before desirable forage is available, limited desirable forage because of drought, after herbicide application, after nitrogen application, yard clippings/waste and animals unfamiliar with the pasture. Also, “sometimes they just eat weird stuff they don’t normally eat,” he said.

Farmers who understand weeds can more effectively get rid of them. Annual weeds are common in overgrazed or highly disturbed areas, such as near a feeding area or water trough. Biennial weeds are common in areas that have been disturbed.

“Biennials are more competitive,” Renz said. “If we have one small disturbance at the right time, we can have a problem. The good news is we can correct it pretty quickly.”

Simple perennial weeds normally have high forage quality. “If not toxic, particularly in a rotational setting, they have good forage quality and are readily eaten,” Renz said.

The high priority weeds are toxic plants, then plants that aren’t palatable, those with low forage quality, plants that reduce pasture productivity and lastly invasive or aggressive weeds that may affect nearby farms but not your pasture.

“We’re all busy and have too much to do, so I focus on prioritizing weeds,” Renz said. “Look on the fence line and the neighbor’s yard nearby for those invasive weeds. If they’re on the roadside, they’re probably in your pasture but you haven’t noticed. But they will be there soon.”

Renz said continuously grazed pastures need more intense weed management. “Animals rarely feed on weeds, which allow them to become large and not palatable, resulting in competition with desirable forages,” he said. That impacts forage biomass and utilization. He recommends rotational grazing as well as fertilizing.

“It increases the competitiveness of those plants against weeds,” he said.

Weeds invade because of a lack of rain, poor fertility, overgrazing/improper grazing timing and non-competitive forages being present. The herd can prove to be a valuable part of a farmer’s weed eradication plan.

“If we keep grazing it before it produces a viable seed, we can get rid of it in three to four seasons,” Renz said.

Overgrazing can promote weed growth if bare ground is present. “That promotes emergence of weeds,” Renz said. “Don’t graze below four inches. Leave a residual height of six inches and higher levels going into winter” – and don’t graze before emergence.

Mowing weeds can help reduce biennial and annual weeds if it’s done just prior to seed production; however, it’s not that helpful for perennials.

“We want to target the correct timing for mowing,” Renz said. “It’s very species-specific. As a rule of thumb, it’s right around flowering. It takes much longer for those plants to regrow. It may flower, but it won’t produce viable seed. If you do it for three to four years, it will go away. With a perennial, you’ll have to do it more often and for a longer period of time.”

Pasture renovation can help reduce weeds if forage grasses are used, since they’re the best at suppressing weeds. “Our legumes get some suppression, but it’s really those forage grasses,” Renz said. “That will produce the most biomass to compete against those weed species.”

Herbicides can also help, but Renz said they bring a lot of negative issues, including environmental and the reduction of desirable forage.

“If you have lots of clovers, this is really problematic,” he said. “We really need to be careful as to how we use herbicide.”