South Dakota Grassland Coalition

by Rick Smith

July 2019

I define a weed as something I don’t want or don’t have use for. A question could be, do my live-stock have the same opinion? All of our responses will be different depending on the species of weed, the location of our operation, and the livestock/wildlife species we care for. It becomes very important to distinguish that all weeds are not of the same cost or value to control, nor do they each exist, proliferate or cause harm to the same degree or manner in a grassland system. Therefore it becomes very important to pick your weed and pick your response accordingly.

Canada thistle, musk thistle or plumeless thistle in my system are ones I truly would like to eliminate. At the same time I have other non-grass species that exist probably performing tasks that I don’t fully appreciate. As of yet, I have not found a livestock only grazing management system that can successfully eliminate the thistle’s existence. A tight window exists when Canada thistle forms buds that livestock seem to relish by nipping them off (see photo to the right), but the window is only a few days. Ten days after the purple shows you have viable seed to deal with. Any form of rotational grazing that keeps livestock out of a pasture during this small 10 day window precludes taking advantage of this grazing tool. Another method to get some use out of the Canada thistle is to mow pre-bud stage and livestock will graze the wilted plant until it dries. Works for cattle, horses and sheep with a small patch, but if it dries out, it becomes ground litter and by fall you will have a new crop sprouted from the roots anyway.

Often we equate weed problems in general to poor grazing management techniques, that result in overgrazing or poor grassland health. In my observation, thistles thrive in high nutrient environments, grass or no grass, managed grazing or not. A few years ago we setup a research site to evaluate 0, 45, 90, 135 lbs/acre levels of urea fertilizer blocked off with three different simulated grazing patterns; continuous, take half leave half, and flashing across repeatedly only taking the top third of plant. After the test was over and the fence re-moved, two years later the sections with the 135 lbs/acre fertilizer rate applied at all types of grazing was solid Canada thistle where none had existed before. Now, I understand why thistles pop up around mineral feeding stations, watering areas, working corrals, or where hay rings have been accumulating excess manure and urine. All of these areas have great grass growing, but often have thistles also.

My preference for control of weeds that both I and my livestock don’t want is to graze intensively what livestock like, move livestock out, followed the next day with non-residual 2,4-D. This seems to achieve my best lasting results without eliminating what my livestock indicate are the good broadleaf plants. Pick your own chemical, insect, mowing or trampling strategy but don’t let thistles go to seed.

Source: SDGC Newsletter

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