The sharp, painful objects often referred to as “stickers” or “burrs” found in lawn grass are actually the specialized seed heads of certain invasive weeds. These spiny seed casings are a reproductive strategy employed by the plant to ensure survival and widespread dispersal. The structures cause irritation and discomfort for people and pets walking across the lawn. Effective management requires understanding that these stickers are reproductive mechanisms.
Common Plants Producing Stickers
Sandbur is a warm-season annual grass identifiable by its light green, flat leaves that resemble crabgrass. It flourishes in dry, infertile, and sandy soils, earning its common name. Sandbur produces clusters of burrs covered in stiff, backward-pointing barbed spines that readily attach to clothing, fur, or skin. This allows the seeds inside to travel great distances.
Lawn Burweed (Soliva sessilis), sometimes called spurweed, is a low-growing winter annual. It germinates in the cooler months, establishing itself as a small, parsley-like rosette. The burrs are small, spiny, and develop within the leaf axils, often hidden close to the soil surface. They become noticeable and painful in late spring and early summer when the plant dries out, leaving the hardened seed pods behind.
Bur Clover is a member of the legume family, recognized by its trifoliate, clover-like leaves. Unlike the sharp spines of Sandbur or Burweed, Bur Clover produces coiled, relatively softer burrs. These burrs are covered in small, hooked prickles that are highly effective at clinging to fabric and animal coats. Identification of the specific weed is important because control methods must be timed to the individual plant’s distinct life cycle.
The Life Cycle of Sticker Weeds
The appearance of sharp burrs is directly tied to the reproductive cycles of these plants, which are predominantly annuals. Annual weeds complete their entire life cycle—germination, growth, seed production, and death—within a single growing season. This life strategy means the plant’s sole purpose is to produce as many viable seeds as possible before it dies.
The timing of germination varies significantly between species. Lawn Burweed, a winter annual, typically sprouts in the late fall or early winter months when temperatures cool down. Sandbur is a summer annual that waits for warmer soil temperatures, often germinating from late spring through mid-summer.
The burr itself is an evolutionary adaptation specifically designed for dispersal, a process known as epizoochory. The spines and barbs allow the seed casing to latch onto the fur of animals or the soles of shoes. This mechanism ensures that the seeds are carried away from the parent plant, increasing the likelihood of successful germination in a new area. Mowing often fails to stop this process and can even spread mature burrs across a wider area.
Strategies for Eradicating Sticker Weeds
Effective management of sticker weeds employs a combination of cultural practices and targeted chemical control, focusing on preventing seed production. Simple adjustments to lawn care can create an environment that discourages weed germination and growth. Mowing the turf at a higher setting, often between three and four inches, helps the desirable grass blades shade the soil surface. This shading reduces the light reaching weed seeds, preventing them from sprouting and establishing a foothold.
Proper watering techniques also reduce weed pressure by encouraging a dense, healthy turf that naturally crowds out invaders. Watering deeply but infrequently promotes strong, deep root growth in the lawn grass, making it more resilient than shallow-rooted weeds. Hand-pulling is a viable mechanical control option, but it must be performed early in the season before the sharp burrs have fully developed and hardened.
Pre-Emergent Herbicides
The most effective chemical strategy involves the precise application of pre-emergent herbicides. These products work by creating a chemical barrier in the soil that prevents seeds from successfully germinating. Timing the application is paramount and must align with the specific weed’s germination cycle.
For winter annuals like Lawn Burweed, the pre-emergent barrier needs to be established in the late summer or early fall, typically around September. For summer annuals such as Sandbur, the application should occur in the early spring, generally when the soil temperature consistently reaches 52 to 55 degrees Fahrenheit. A single, well-timed application can prevent the emergence of thousands of plants that would otherwise produce painful burrs later in the year.
Post-Emergent Herbicides
When plants have already matured and are visible in the lawn, post-emergent herbicides are necessary to kill the existing vegetation. These products are designed to be absorbed by the foliage, moving throughout the plant’s system to kill it completely. However, once the burrs have hardened, applying a post-emergent herbicide will kill the plant, but the sharp stickers will remain on the ground until natural decomposition occurs.
Selecting the correct post-emergent product requires knowing the type of grass in the lawn, as some herbicides can damage certain turfgrass varieties. Selective herbicides containing 2,4-D, dicamba, or MCPP are often used for broadleaf weeds like Burweed. Treating grassy weeds like Sandbur requires different active ingredients, such as quinclorac. Applying these chemicals when the weeds are small and actively growing ensures the highest rate of success before the reproductive stage is reached.