High Density Grazing for Spotted Knapweed Suppression

When we first moved to Idaho in 2004 we were introduced to the presence of invasive noxious weeds in the pasture on the small property we had purchased. Back in Missouri we had some thistles and ragweed which seem to be present to some degree in almost every pasture back in the Midwest. What we weren’t used to was the legal mandate requiring us to control those weeds on our property. Most landowners in the area routinely spray their pastures for control of those noxious weeds. In the 20+ years we had been on our farm in Missouri, I had never once sprayed one ounce of herbicide for weed control. Since everyone else in the neighborhood was spraying their weeds, I felt enough peer pressure that I did it for a couple of years. I didn’t like doing it as we were already quite deficient in legume content in the pasture and there were other beneficial forbs I would have liked to have present in the pasture. Looking around the neighborhood, it was painfully apparent that those good citizens who had been spraying religiously for the last 10 years still had plenty of knapweed to go around. I quit spraying and just let the cattle we were custom grazing there for a neighbor eat what they would. I have to admit the knapweed presence in the pasture steadily increased ove

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5 thoughts on “High Density Grazing for Spotted Knapweed Suppression

  1. This may be a good way to utilize spotted knapweed but the article leads us to believe that cattle grazing is eliminating the knapweed from the pasture.Author states that there’s no knapweed in photos – maybe appararently, but with knowledge of knapweep morphology, I’m sure the plants have been utilized but not eliminated, and grazing alone won’t eliminate knapweed. I researched knapweed control with sheep at the US Sheep Station, 2000-2002. Sheep will select spotted knapweed and develop a preference for the nutritious plant, and graze it through the season, rosette, flowering and seed set stages. Sheep will select the nutritious parts with their prehensile lips even late in the season. Intensive grazing with cattle as the article describes would work but I doubt the cattle are developing preferences for the weed as choice is eliminated in the high density scenario, and the perennial plant can withstand intensive grazing in the short term. It’s good to see grazing in the IPM strategy, but I’d like to see more monitoring to evaluate a trend in the pasture. Sometimes pictures aren’t enough.

    1. Hi, Michael!
      Like you, I’ve studied grazing spotted knapweed for some time, but from a slightly different perspective. From work done by Fred Provenza and his colleagues at Utah State University about how animals learn what to eat, I learned that animals choose based on what they’ve learned from their Mother and herd mates, and on the internal feedback they get from a plants nutrients and toxins. That means spotted knapweed, with good protein (10-19% depending on growth stage) is good forage and if we can get animals to try them, they are likely to keep on selecting them in pasture. That’s just what I found when I trained cattle. Year after year, they chose more and of the weeds, allowing the grasses to grow as well. That’s why I was so excited to see this project by Jim Garrish. He’s now created a herd that will eat this plant and help him suppress knapweed. He’s reduced costs, and increased forage so it’s a good deal all around. And as you noted, the weeds aren’t gone with one grazing, but as the animals return year after year, they’ll continue to work for us.

    2. Hi Michael,

      I have to say it never occurred to me that anyone would think the knapweed could be eliminated with a single grazing. I suppose there are some readers of On Pasture unfamiliar with any aspect of weed ecology who might think that way. Thanks for bringing it up.

      In the beginning of the article I said the objective was suppression of seed production. That we clearly accomplished.

      What Kathy said about training animals early in life is spot on. The neighbor whose cows we were grazing has said in the past that his cow herd now eats more knapweed than in the more distant past. We have been grazing his heifers with exposure to knapweed in a high stock density situation for the last 7 years. This was the first year we used UHSD in a targeted window of growth. Yes, we will be doing this for several years and monitoring the results.

      The main cow-herd on the ranch unit we manage readily eat knapweed without being pressured to it after many years of exposure. Our main problem here is delivering the pressure at the optimal growth stage for suppression of seed production. I will start working on that in 2016.

      Jim G

      1. Great comment Kathy and your success as stated and provided with photos are commendable Jim. Here in Missouri our ranch grazes about 2000 head of sheep, goats, and cattle on 1100 acres. We depend upon and propagate many species of so called weeds to satisfy the nutritional requirements of our dense mixed herd. As you mentioned the high protien content of the knapweed I would encourage more ranchers to utilize these types of great sources of feed stuffs particularly considering the low cost of seed and its application costs. Good job.

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