Don’t let weeds put your cattle in a corner

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Overgrown pasture weeds

Forage surrounding undesirable species goes ungrazed because of physical and chemical barriers. 

The prospects for higher grain prices, drought-tightened hay inventories and market uncertainty provide ample incentive to focus on maximizing pasture production this grazing season. Don’t overlook the underused or, in some cases, the unused acre.

“Cattle tend to stay clear of weedy areas due to physical or chemical barriers, resulting in grazing avoidance,” explains Scott Flynn, zonal biology leader with Corteva Agriscience. A physical barrier can be stickers, thorns or sharp spines that hurt a cow’s mouth and nose. The chemical composition of certain weeds simply makes them unpalatable to livestock. Leafy spurge contains a white, milky sap that irritates mouths. Other species — such as lupine, poison hemlock or crazyweed — can be toxic.

“It’s easy to understand why cattle avoid grazing near weeds with thorns or stickers,” Flynn says. “What’s often more difficult to grasp is just how much grazing access those weeds cost.”

Consider bull thistle, for example. First, its prickly leaves keep grazing animals from sticking their noses in among its leaves to take bites of available grass. But research shows the fencing-out effect extends beyond the physical barriers the thorns create. Cattle avoid grazing within a 4-inch ring around the diameter of the thistle’s rosette. Together, these avoidances in and around bull thistle can reduce forage utilization by 42%. Musk thistle hits utilization even harder with a 72% loss.


When cattle start to avoid areas because of weed populations, they tend to focus on and overgraze areas with better access to desirable forages, weakening those areas and creating new opportunities for weeds to encroach.

“Even relatively light weed infestations initiate change in the pasture,” Flynn notes. “Grazing avoidance leads to uneven grazing and poor utilization of forage. Left alone, broadleaf weeds gain a competitive edge and pasture decline continues.

That’s why, Flynn says, it’s important to address these issues early to prevent further decrease in grazable acres, especially during a year when an extra emphasis on holding the line on feed costs has an even larger impact on profit potential.

“Weed control can increase grazable acres, along with overall forage production,” Flynn says. “But then crossfencing, water distribution and other practices designed to enable better grazing management can help increase per-acre productivity.”

Learn more about these barriers and how eliminating them can help maximize profit per acre at


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