High Density Grazing for Spotted Knapweed Suppression

It’s that time of year when we begin to think about weeds in our pastures. So I’m bringing back this great piece from Jim Gerrish showing how he managed to reduce a particularly problematic weed using a high density grazing program. Be sure to check the comments at the end where Jim adds additional information about grazing and weed management.

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.

Spotted knapweed is a very nutritious plant with 14 - 20% protein in the rosette stage and 10-12% when it's bolting. It's a great forage!
Spotted knapweed is a very nutritious plant with 14 – 20% protein in the rosette stage and 10-12% when it’s bolting. It’s a great forage!

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 over those several years. It was getting bad enough I decided I needed to be a little more proactive to keep the county from coming to spray my field and handing me a bill for their diligent service.

A quick read of the existing literature on grazing for knapweed control suggested the window of opportunity for making a meaningful impact on the weed was between early bud and full bloom. The research said knapweed grazed severely during mid to full bloom experienced over 90% reduction in seed yield. In the past we had started our grazing while the knapweed was in a vegetative state and never delivered enough grazing pressure to force the cattle to eat the knapweed once it began blooming. The pasture we are working on is 16 acres of wild flood land and we generally have had 30 to 35 replacement heifers and a bull for about five weeks of grazing.

In 2015 we had 36 heifers and the bull arrive on June 25, about two weeks later than in the past. The knapweed was in very early bud stage for the first grazing strip. As we worked our way across the field with daily moves at about 60,000 lbs/acre stock density, the blooming of the knapweed advanced as well. Once we hit early bloom, I pushed the stock density to over 100,000 lbs/acre still using daily moves. At full bloom, I shifted to 2 or 3 moves per day with the stock density in the 300,000 to 400,000 lbs/acre stock density. All through this, I was closely monitoring rumen fill and behavior of the cattle to ensure we were not compromising animal performance while pushing for high knapweed utilization.

We made our first grazing pass across the 16 acres in about 5 weeks and then went over what we had grazed early for another three week period. The part of the pasture that we hit after mid-bloom was only grazed once, while what we had grazed at a less mature stage was grazed a second time with the plants at full bloom or even more mature.

Here is grazing spotted knapweed at full bloom. In the foreground you see where the cattle will be grazing the next day.

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This is what it looks like behind the cattle following 2x per day moves.

What it looks like behind the cattle following 2x per day moves

This is the set up for the 3 moves per day. Grazing is just a matter of leap frogging a 100 foot piece of polytape ahead for the next move.

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This is the outcome of 2x per day moves on the right compared with 1x moves where the cattle are on the left. Note the greening up on the right strip. the cattle have been off that pasture for 4 days.

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Here we’re grazing a mixture of spotted knapweed and yellow toadflax. Note the cabin position in the background and the one large sagebrush clump.

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This is the same spot at the the photo above, just 24 hours later.

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This is the same spot as the 2 photos above 6 weeks later. Note the very low density of knapweed plants and the low number of blooms. While it may not look like that much recovery on the pasture, we do not plan to have cattle here again until late June of 2016.

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A broader view of the field six weeks after grazing was completed. There are very few weeds to be seen.

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Overall I was very pleased with the outcome of this single season of heavy grazing pressure during the blooming phase of growth. Evaluating the pastures a month after the end of grazing showed very few knapweed plants with any more than a half dozen flowers. Many plants were just stem stubs with a few leaves and one or two flowers.

We will repeat the timing and severity of grazing in 2016 and reevaluate the outcome next fall. County weed guys never stopped by to see what I was doing, but they also bypassed spraying my outlaw pasture one more time. If we have good success in 2016, I might invite them over to have a look.

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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