Invasive plants can be controlled by grazing, mowing, and biodiversity

— Photo by Gary Kleppel

A winter-dormant stand of spotted knapweed runs along a boundary between Gary Kleppel’s and a neighbor’s property to the left. There is no knapweed on the neighbor’s property because he mows it. There is no knapweed on the left because Kleppel’s sheep graze it.

— Photo by Gary Kleppel

Gary Kleppel treated a small, dense stand of spotted knapweed with a technique called mob grazing. He kept his sheep close together and notes, “Pretty soon everybody is scarfing down everything they can get into their mouths.”

To the Editor:

The testimonies of Kevin Crosier and Emily Vincent to the State Assembly’s agricultural committee described in last week’s Enterprise speaks to the desperation many farmers feel when dealing with invasive species. Invasive plants cost the nation billions in agricultural production each year. The call by Cornell University Professor Antonio DiTomasso and the Natural Heritage Program’s Dr. Jennifer Dean for crucial research into the control of invasive plants should not be ignored. 

Several years ago, I published a research article in the scientific journal that Dr. DiTomasso edits. It dealt with the potential use of livestock for controlling the invasive plant purple loosestrife. The research site was Slim and Cathy Newcomb’s farm in East Berne. I, like many scientists, farmers, and ranchers have found that livestock — cows, goats, sheep, and pigs — can be effective at managing invasive plants. While livestock won’t completely eradicate invasives, they often change the role of these plants from being invasive to being just plain plants.

On our farm in Knox, we use three techniques — grazing, mowing, and biodiversity — to manage invasives. I have never used chemicals on my pastures or lawns; they are expensive, dangerous, and I just don’t need them. Herbicides are generally indiscriminate in what they kill. They damage the plant community and the soil microbes that are so important to soil and plant health. In addition, several widely used herbicides are associated with human diseases and disorders such as autism, hypertension, and cancer.

Several plant species classified as invasive live on our farm, but they only produce dense stands in places where we either don’t mow or don’t graze our sheep. In the photo here, taken on Dec. 10, a now winter-dormant stand of spotted knapweed runs along a boundary with my neighbor’s property to the left.

You’ll notice that there is no spotted knapweed on his property. He mows it. But there is no spotted knapweed to the right of the stand, on my property, either. That’s because my sheep graze it. The right-hand edge of the spotted knapweed stand demarcates my electric fence line.

About once every 30 to 40 days, I enclose the area shown in the photo with moveable electric fence and allow my sheep to feed there for one to one-and-half days at an equivalent stock density of three to four tons of sheep per acre. That’s 300 to 400 percent higher than conventional stock densities.

The sheep put intense pressure on the plants in the pasture, but for so little time that you would barely notice that the pasture was grazed after they’ve moved on. As a result of this “intensive rotational grazing” approach, which mimics the way wild ungulates graze, a little spotted knapweed is always present in the pasture, but never at a level that would be considered invasive or damaging to the biodiversity of our pastures.

In fact, between 2009 and 2018 the number of different kinds of plants in our pastures increased 12-fold. Our grazing techniques enhance the biodiversity (i.e., the number of different kinds of plants) in our pastures and they keep wannabe invasives in check. The places where we graze our sheep rarely need mowing (reducing fuel costs).

Last summer, I treated a small, dense stand of spotted knapweed in an area that we don’t usually graze, by a technique called mob grazing. The knapweed was living among some shrubs and saplings that I also wanted to get rid of.

I moved my sheep into that area (as illustrated in the photo), keeping them very close together (the equivalent of nearly 10 tons/acre). When sheep are close together and they see their neighbors eating, they become concerned that their neighbor is going to get all of the food. So they start eating. Pretty soon everybody is scarfing down everything they can get into their mouths.

After I moved my sheep into the “target” area, I sat in a lawn chair and read a book, while my border collie made sure everyone stayed where they were supposed to. Within an hour, the spotted knapweed was eaten down to the dirt.

We returned once more during the summer; there was very little spotted knapweed around. We returned again in November and found abundant grass but no evidence of knapweed.

Intense infestation of a hayfield by spotted knapweed may obviate hay production, but short, intense bouts of mob grazing several times over the course of one or two seasons might help get the invasive under control while allowing the land to retain some of its value by feeding livestock.

Frost seeding with pasture grasses and red clover and further cover cropping during the season might help as well. The length of the recovery period will depend on the intensity of infestation and how well the invasive can be controlled by the emergent increase in biodiversity.  

We have wild parsnip on our farm, mostly along drainage ditches that aren’t grazed. That we don’t find it in our pasture, suggests that our sheep manage it. When wild parsnip overruns a pasture, as it has at Emily Vincent’s Two Rock Ranch, toxin levels may obviate grazing.

Frequent (weekly) mowing, beginning in early spring, may help thin the invasive by depriving it of the capacity to produce food by photosynthesis. Initially, the plant will put a great deal of the energy stored in its roots into the production of stems and leaves to permit photosynthesis. This is the only way the plant has to produce food.

Keep mowing! Don’t allow the plant to produce leaves. Ultimately, it will begin to starve and either go dormant or die.

I don’t know how long this takes in parsnips, but without photosynthesis the plant has to starve. As you mow, seed a low-growing grass (e.g., Kentucky bluegrass) and white clover, that won’t be affected by mowing.

In late winter, frost seed Timothy or orchard grass, and red clover. In the spring, if the density of wild parsnip is reduced, put sheep on at the equivalent of three to five tons per acre, for no more than a day. If nobody presents with burns or morbidity, the pasture may be useable.

But after a day of grazing let the pasture rest for at least two weeks. Continue intensive rotational grazing coupled with seeding of grasses and cover crops to allow continued pasture recovery.

Certainly not every invasive plant can be managed by grazing, mowing, and the encouragement of biodiversity. Nor can every infestation be reversed by these techniques. But they have been used successfully all over the world (including here in the Hilltowns). So, if you’re having a problem with invasives, it may be worth a try.  

Gary Kleppel


More Letters to the Editor

The Altamont Enterprise is focused on hyper-local, high-quality journalism. We produce free election guides, curate readers' opinion pieces, and engage with important local issues. Subscriptions open full access to our work and make it possible.