Sand burrs (Cenchrus species) are a widespread annual pest that significantly degrades pasture forage quality. These plants produce sharp, spiny seed heads that cause discomfort and injury to livestock and humans. The burrs reduce the economic value of pastureland by making forage unpalatable and decreasing animal health. Effective management requires a multi-year, integrated approach combining cultural, mechanical, and chemical strategies to reclaim infested areas.
Understanding the Sand Burr Threat and Life Cycle
Sand burrs are warm-season annual grasses that thrive in dry, sandy, or disturbed soils. While some perennial varieties exist, identification in the vegetative stage involves recognizing their grass-like appearance. They feature a light-colored, hairy leaf collar with a finely cut ligule, distinguishing them from desirable pasture grasses. The most recognizable feature is the mature inflorescence, which forms a spiny bur containing seeds.
The annual sand burr life cycle begins with seed germination in the spring when soil temperatures reach approximately 52 degrees Fahrenheit. Germination continues throughout the summer, creating multiple flushes of new plants. Plants produce their sharp burrs (seed heads) from summer until the first hard frost. These spiny burs are highly effective at dispersal, easily clinging to animal fur, clothing, and equipment, allowing rapid spread across a pasture.
The negative impact on livestock is a primary concern for producers. Sharp burrs cause painful mouth sores and digestive issues when ingested, leading to reduced grazing and weight loss. The burs also become embedded in the hide and wool of livestock, reducing the market value of animals and their products. Control efforts are most effective when timed to interrupt this annual cycle before the burrs mature.
Immediate Non-Chemical Control Methods
Mechanical and cultural methods can immediately reduce sand burr populations, focusing heavily on precise timing. Mowing is a suitable physical control option only if performed before the burrs develop hard, viable seeds. Mowing too late in the season inadvertently spreads mature, spiny seeds, exacerbating the infestation.
Optimal mowing involves setting the blade height high to favor the desired forage grass and help it compete with the sand burr. For small, localized infestations, hand removal or spot treatment is feasible, provided the entire root system is removed. This manual method prevents the plant from setting seed and is best done early in the season when plants are small.
Targeted heavy grazing can be used as a cultural suppression technique early in the spring. Immature sand burr plants are palatable to livestock before the spiny burrs form, allowing animals to graze and suppress growth. Once burrs are present, grazing is no longer advisable. Overgrazing should also be avoided as it creates bare soil ideal for sand burr establishment.
Strategic Herbicide Application
For large or heavily infested pastures, a strategic chemical program is necessary, requiring careful selection between pre-emergent and post-emergent options. Pre-emergent herbicides, such as those containing pendimethalin (Prowl H2O) or prodiamine (Barricade), are applied in late winter or early spring to prevent seed germination. This application must be timed accurately to occur just before the soil temperature reaches the 52 degrees Fahrenheit germination threshold.
Post-emergent control targets actively growing sand burr plants that have already emerged. Effective selective herbicides include Pastora (metsulfuron-methyl + nicosulfuron) or Plateau (imazapic). These minimize damage to desirable perennial forage grasses like Bermuda grass. These products are most effective when applied to small, seedling sand burrs, less than two inches tall. Perennial sand burr varieties, which regrow from old crowns, often require a tank mix of a selective herbicide with a non-selective product like glyphosate.
All herbicide applications must adhere strictly to the product label instructions, especially concerning grazing restrictions and hay withdrawal periods. For instance, Pastora has no grazing or haying restrictions, making it a flexible option. Prowl H2O, however, requires a 45-day waiting period before grazing. Applying these chemicals when the forage grass is dormant or immediately after a hay harvest minimizes contact with desirable plants and maximizes coverage on the sand burr.
Long-Term Prevention Through Pasture Management
Long-term sand burr control relies on improving the overall health and density of the pasture, as the weed thrives in sparse and bare soil. Soil testing is a fundamental first step, allowing for the correction of pH and nutrient deficiencies through targeted fertilization. Promoting vigorous growth of forage grasses makes them more competitive, naturally crowding out sand burr seedlings.
Increasing competition involves overseeding with aggressive, desirable perennial forage grasses, such as Bermuda grass or Fescue, to create a dense canopy. A thick stand of healthy grass prevents sunlight from reaching the soil, inhibiting the germination and establishment of new sand burr plants. Proper nitrogen, phosphorus, and potassium levels are necessary to support this dense, competitive growth.
Implementing a rotational grazing system is another key management practice that prevents the creation of bare spots where sand burrs easily establish themselves. Managing the grazing pressure ensures that livestock do not graze the forage too low, maintaining a healthy root system and a thick grass cover. Consistent, multi-year application of these cultural practices reduces the need for constant chemical intervention and steadily reclaims the pasture.