The spiky structures found on certain grasses are specialized reproductive parts called seed heads. These dried, bristly formations are a natural outcome of the grass plant completing its life cycle, typically occurring late in the spring and throughout the summer. Their sharp design allows them to detach easily and poses a concern for people and animals moving through grassy areas. Understanding their biological function is the first step toward managing the risks they present.
Biological Purpose of Awns and Burrs
These abrasive grass parts serve the purpose of propagating the plant far from its parent. The stiff, bristle-like extension found on many grass seeds is called an awn, while a burr is a seed or fruit encased in a structure covered with hooks or prickles. Both structures are highly adapted for dispersal, the movement of seeds away from the original plant.
One primary dispersal method is epizoochory, where the awns and burrs attach themselves to the fur or clothing of passing animals and humans. The small barbs hook onto a surface, allowing the seed to be carried over a significant distance before dropping off. This strategy ensures the plant can colonize new habitats and reduce competition with the parent plant.
Another function involves mechanical self-burial, particularly in species like wild rye. These awns are hygroscopic, meaning they twist and untwist in response to changes in humidity, making the seed “walk” across the soil surface. This motion pushes the seed head until it finds a crevice and burrows into the ground for germination.
Identifying Common Problematic Grasses
The structures causing the most trouble belong to species like Foxtail Grass and Sandbur. Foxtail Grasses (Setaria species) are annual grasses known for producing a bushy, cylindrical seed head that visually resembles a fox’s tail. These non-native plants are commonly found along roadsides, in fields, and in disturbed ground, where they flourish from late spring into the summer.
The danger begins when these seed heads dry out, becoming brittle and easily detached from the plant stalk. Other culprits include the Sandbur, which develops hard, globe-shaped fruits covered in sharp spines, and Cheatgrass, which produces needle-like awns. Identifying these grasses is important, as they thrive in dry, overgrown areas and are most hazardous when mature.
Health Risks to Pets and Humans
The barbed design of awns and burrs makes them hazardous, especially to pets. These structures are shaped like small darts with backward-pointing spikes. The unidirectional shape means that every movement of the host, whether walking or scratching, drives the seed head deeper into the tissue.
For animals, the most common entry points are between the toes, in the ears, up the nose, and into the eyes. If inhaled, a grass awn can migrate through the nasal passages toward the lungs, potentially causing severe respiratory issues like pneumonia. When embedded in the skin, the migrating awn often causes localized infection, leading to abscesses or persistent draining tracts.
Awns lodging under the eyelid can cause painful corneal ulcers and may result in vision impairment if not removed promptly. Those entering the ear canal can puncture the eardrum, causing chronic ear infections or neurological symptoms if they move further inward. While less common in humans, these structures can cause skin irritation or become lodged in clothing, sometimes leading to localized inflammation.
Practical Management and Removal
Managing the presence of these problematic grasses involves reducing the number of mature seed heads. Mowing frequently before the grass develops and dries out its seed heads can significantly reduce the hazard. Hand-pulling individual plants before they set seed is an effective way to remove them entirely, especially in smaller areas.
For larger areas, applying selective herbicides or using plant growth regulators (PGRs) can help suppress the grass’s ability to produce viable seeds. PGRs limit the plant’s vertical growth and reduce the number of seed heads that emerge, lowering the risk of dispersal.
Owners of pets should perform a thorough physical check after walks, particularly during the late spring and summer. Attention should be paid to the fur, the spaces between the paw pads, inside the ears, and around the eyes. Removing any attached awns or burrs immediately prevents them from burrowing into the skin and causing serious problems.