Use integrated pasture weed control

By Dean Slates

Probably no aspect of modern agriculture has changed more than our attitude and approach to pasture management. Heading the list of changes has been our approach to pasture weed control.

As a teenager on our farm in Carroll County, it was one of my summer jobs to do the “annual pasture mowing” with the old John Deere B. Some time in July or August, I’d head out to clip the iron weeds and bull thistles and whatever else was “standing tall” on those hills.

As I recall it, we could really grow bull thistles and iron weeds. And, as I recall it, as the years passed, those annual mowings never seemed to reduce the size or number of those “monster” weeds from one year to the next.

Better approach. While we still have farm boys and their dads who continue to perform those “ritualized annual pasture mows,” there is a better approach to pasture weed control.

It occurs to me that if a plant is readily eaten by your livestock regardless of the species, it is a misnomer to call it a “weed” in the pasture.

That name, “weed,” should more correctly be reserved for those plants that the livestock can’t eat or, won’t readily eat, or would be toxic if they were eaten.

Under the weed moniker umbrella we would include plants like the ironweed, bull thistles, and multiflora rose; but it also includes plants like orchard grass, reed canary grass, and tall fescue that have been uneaten and gone on to produce seed heads. When they are in the vegetative state, these grasses can be very nutritious forage; but when they get mature, they become lignified and very unpalatable to most livestock. They take up space that could be used to grow forages that the animals will eat.

Soil fertility. The first step in pasture weed control is to get the soils analyzed to see if fertilizer or lime is needed to allow for optimum growth of desirable pasture plants. Having that assured, you are ready to get control of the weeds.

Clip pastures. Clipping is the first choice for pasture weed control. Frequent and low cutting to keep all plants growing in the vegetative state.

If you are just now “embarking” on serious pasture weed control, this may mean clipping at three week intervals, or after each pasture rotation. This needs to start in May and continue as long as there is uneaten materials after the livestock complete a graze.

Some weeds, like bull thistle and iron weed, will succumb in a single season of frequent clipping. Research and experience has shown that the mowing regimen can be reduced in future years, but the first season’s mowing efforts need to be very intense to achieve actual weed control results.

Herbicides. Some pasture weeds may best be controlled by the selective use of selective herbicides, but herbicides are problematic in the pasture.

The 2002 issue of “Weed Control Guide for Ohio Field Crops (Bulletin 789 available from your OSU Extension office) lists several herbicides that are labeled for pasture weed control.

The first problem posed by herbicides is that, even though they are “selective,” they will kill desirable broad leaf forage plants in addition to the weeds. Participants in grazing schools have heard me state that the “threat” of using dicamba or clopyralid or one of the other broad leaf weed herbicides is enough to kill the clovers, or the alfalfa, or trefoil or lespedeza plants in your pasture.

While it actually takes more than a “threat,” the point is that most of the herbicides labeled for grass pastures are deadly to your most valuable, and nutritious, pasture plants. The second problem is grazing restrictions. You need to carefully read and follow all instructions on herbicide product labels to be sure that the products fit your livestock operation.

Not all herbicides have grazing restrictions, but many do. If it says “do not graze … ” that is exactly what you must do.

Probably the best option is to spot treat serious weed patches with herbicides and try to do the least damage to the desired forage species you can. No matter what, herbicides are problematic, albeit effective.

Integrated pasture control. When it is all said and done, effective pasture weed control requires an “integrated approach.” You do what is required to optimize forage plant growth. You rotate the graze and clip what is not eaten. And, you selectively use herbicides when the other approaches don’t get the weeds under control.

The plants that proliferate in the pasture are the ones that can thrive in or tolerate the environment you provide. If the ones that seem to grow best are “undesirables,” then the solution is as simple or difficult as adjusting the growing environment in favor of the desirable forage plants.

Effective pasture weed control is more than just once-a-year mowing or spraying with an herbicide.

(The author is the OSU Extension Agriculture and Natural Resources Agent in Holmes County. Questions or comments can be in care of Farm and Dairy, P.O. Box 38, Salem OH 44460.)