Clover is a common broadleaf weed that frequently invades grass-dominant pastures, posing significant health and management concerns for grazing horses. Effective removal and long-term control of this resilient plant require a thoughtful, multi-pronged approach. This strategy combines immediate manual and chemical interventions with long-term cultural and soil management. The goal is to create an environment where desirable grass species can thrive and naturally exclude the weed.
Understanding Why Clover Needs Management
The presence of clover in a horse pasture introduces specific risks to equine health beyond aesthetics. One danger comes from Alsike clover (Trifolium hybridum), which causes photosensitivity, leading to severe sunburn-like lesions on unpigmented skin. Long-term consumption of Alsike clover is associated with “big liver syndrome,” a progressive and potentially fatal liver failure.
Red and White clovers (Trifolium pratense and T. repens) are generally less toxic but can cause “slobbers,” or excessive salivation. This occurs when they are infected by the fungus Rhizoctonia leguminicola, which produces the mycotoxin slaframine. Slaframine stimulates the horse’s salivary glands, causing dramatic but usually non-life-threatening drooling. Clover is also a legume that fixes nitrogen, resulting in forage with a significantly higher crude protein content than most grasses. This high nutritional density can lead to over-conditioning and weight gain in horses with lower caloric needs, disrupting a balanced diet.
Manual and Cultural Control Methods
For small, isolated clover patches, manual removal is a practical and immediate method of control. White clover has a relatively shallow root system, making it easier to pull by hand, especially when the soil is moist. When hand-pulling, remove the entire root structure to prevent regrowth from remaining fragments.
Mowing is an effective cultural practice used to stress clover and encourage grass competition. Since clover is low-growing, an initial low pass can cut off flower heads, preventing seed production. Immediately afterward, raise the mower height to four inches or more to promote taller grass growth. This increased height allows grass blades to shade the clover, reducing the sunlight the weed needs to thrive.
Rotational grazing is another management technique for weakening clover stands. Horses often graze selectively, consuming clover first due to its palatability and high sugar content. By dividing the pasture into smaller paddocks, you control grazing intensity and duration. A common practice is to graze the pasture down to a residual height of three to four inches, then rest it for 21 to 30 days. This rest period allows desirable grass species to fully recover and outcompete the clover.
Selective Herbicide Application
When clover is widely established, strategic application of selective herbicides is the most efficient removal method. The most common active ingredients for broadleaf weeds like clover are 2,4-D, Dicamba, and MCPP, often used in combined products. These formulations target and kill broadleaf plants while leaving desirable perennial grasses unharmed.
Timing the application is important to maximize effectiveness against perennial clover. Fall application, ideally in late September or October, is often the most effective time. During this period, the clover plant actively moves carbohydrates to its root system in preparation for winter. The herbicide is translocated along with the carbohydrates, resulting in a better kill of the entire plant, including the roots. Spring spot treatments are also effective when the clover is actively growing and still small.
Safety protocols regarding grazing restrictions must be followed precisely. While some 2,4-D products may allow horses back once the spray has dried, many combination products have mandatory withdrawal periods. It is important to read the product label carefully, as restrictions can range from a few days to over a month, especially for lactating mares or animals intended for slaughter. Additionally, never harvest hay from a treated area until the label-specified restriction period has passed, as chemical residue can persist in the dried forage.
Maintaining a Clover-Resistant Pasture
Long-term clover control requires altering the pasture environment to favor grass growth over the weed. Clover is a nitrogen-fixing plant, meaning it thrives in soils with low nitrogen levels, a condition that stresses grass. Therefore, the first step in prevention is a comprehensive soil test to determine the pasture’s current pH and nutrient profile.
Clover prefers acidic soil, and a pH below 6.0 is highly conducive to its establishment. Applying agricultural lime according to soil test recommendations will raise the pH to a range more suitable for grass, typically between 6.0 and 7.0. Applying nitrogen fertilizer will also shift the competitive advantage toward the grasses, helping them grow taller, denser, and more aggressively.
Overseeding the pasture with aggressive and resilient grass species is another crucial component of a long-term strategy. Excellent choices for horse pastures include endophyte-free tall fescue, orchardgrass, and perennial ryegrass. These grasses establish a dense sod that physically crowds out low-growing clover and prevents new seedlings from establishing. Proper watering and drainage management will further support the deep, healthy root systems of the desirable grasses, ensuring they maintain their competitive edge.