Make Pastures More Resilient to Weed Threats


Poor grazing management is among the leading causes of many pasture weed issues. This frequently relates back to overgrazing, explains retired University of Kentucky weed scientist Bill Witt.

“In established pastures, Witt stresses producers practice managed grazing and be observant.”

"By overgrazing, you reduce the forage's ability to suppress weed growth," says Witt.

On the other end of extremes, Witt notes, weed issues can also arise if pastures are under-stocked. When producers are only grazing a few animals, they may not see any incentive to control problem weeds. Instead, Witt says, producers usually do nothing and eventually end up with the same problem overgrazing leads to - too many weeds.

Thistle in pasture"In many areas, if you let those weeds, particularly woody plants, start to encroach, you will get into some very serious issues," says Witt. "Then you're not dealing with herbaceous plants that are easy to control. You've got woody brush or trees that are much more challenging."

In the spring, Witt points out there are a variety of weeds pasture managers must keep an eye out for. Species present, of course, will vary by region. In his area of Kentucky and the surrounding Midwest, Witt lists the following problem weed types as some common examples:

  • Biennial species like musk thistle, bull thistle and poison hemlock
  • Perennials such as Canada thistle and tall ironweed
  • Annuals including common ragweed, spiny pigweed and cocklebur

Weeds in pasture where cattle grazeWith these three very distinct groups of plants in most pastures, Witt says many producers may be unsure which to attack first as each poses a threat during very different times throughout the grazing season. For example, some of the herbicides that are efficient at controlling biennial thistles and other weeds early in the spring are not as good at controlling perennials like tall ironweed which come up later in the summer. To be effective against the parcel of weed threats listed, Witt explicates, pastures should ideally be sprayed two to three times through the season.

More times than naught, however, Witt says, weeds do not get sprayed because producers either do not have the time or the funds to spray pastures multiple times during the grazing season. As an alternative, he says, pasture managers should identify the most troublesome weed problem and start there.

Ragweed is a threat to health of pastures and livestockFor instance, says Witt, "If you think tall ironweed or another perennial like Canada thistle is the main problem in your pastures, then start with cleaning that up."

On the order to target weed threats, Witt says, "Get your toxic plants out first if you have any, then those that inhibit grazing the most, and then follow up with any weeds that reduce your forage yield."

When it comes to which herbicides to choose, Witt says, begin by learning which products are registered in your state.

"There are so many herbicides out there, that if we wanted, we could control, frankly, every weed in our pastures. But that isn't always feasible or doable," says Witt.

Pasture Management eliminates weedsThe most important thing, Witt says, is to make sure herbicides are sprayed at the right time of year and rate to control the weed in question. Many state agencies and university extension programs have publications that talk about pasture management or weed control.  He recommends checking with your local extension agent, USDA, or NRCS office for more information.

Along with controlling problem weeds, Witt says there are many proactive measures pasture managers can take to make their grazing lands more resilient against weed threats. For new pasture seedings, in particular, he suggests paying close attention to seeding rates, time of seeding, and making sure there are no weed issues present at time of planting. In particular, he says, grazing of newly established pastures should be monitored closely.

"Everywhere we lose desirable plants, weeds will come in to occupy those places," says Witt. "So don't overgraze."

Cow standing in weedy pastureIn established pastures, Witt stresses producers practice managed grazing and be observant.

"If you see a new weed pop up, go out there and remove it, spray it, kill it, whatever. Just don't let them go to seed," says Witt. "Once those seed banks are established they are basically there forever."

Additionally, Witt emphasizes soil fertility should be of concern.

"We don't think a lot of nutrients are removed from grazing. It's true, as animals consume forage, a portion goes back to the ground, but we remove several pounds of nitrogen, phosphorus, and potassium, as well," says Witt.

"Many times pastures are also used to graze and cut hay from," comments Witt. "When that happens it's even more important to manage soil fertility because even more nutrients are removed."

Tractor Brush Hog PastureWitt advises producers to test pastures for fertility every so often, at least every three to five years. Inherent soil fertility will vary by region, but the important thing is to pay attention to soil health. Fertile soil equals to good forage growth, which in turn, means fewer weeds.

Lastly, Witt dispels the myth of mowing as an effective weed control strategy.  The problem lies, he describes, in the mowing height needed to control annual weeds. Annuals must be mowed very close to the ground to get effective weed suppression, but this goes against the common practice for forage crops.

"If you mow low and it's the right time (plant stage), you can prevent seeds from being produced," says Witt. "But if weeds have already produced a seed, which frequently happens when we don't mow till late in the summer, all we've done is made the problem worse. Also, most people mow with a bush hog (rotary mower) which just blows seed everywhere."

In the end, Witt makes clear good pasture weed management comes down to doing three things - being on time, proactive, and observant. By paying attention to what's happening in pastures and taking action as soon as weed threats arise, pastures will be more healthy and resilient on the whole.

Authored byJesse Bussard.

Cattle grazing healthy green pasture

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