Some weeds are easy to remove and succumb quickly to chemical or organic lawn treatments. Other weeds produce sharp spiny seed heads called burs and can be difficult, or painful, to control. Burs are produced as a protection mechanism for the plant and helps the seed attach itself to anything it contacts, including automobile tires. This allows the weed to invade large areas of the country.
The southern sandspur, field sandbur or grassbur (Cenchrus echinatus) is an annual weed that appears during the summer months when the soil is warm. It thrives in poor dry soil and grows in barren patches where there is little competition. The growth habit is broad and flattened and the grassy leaves radiate up to 18 inches from the center. The stiff spiny seeds are held slightly above the leaves where they easily attach to clothing or passing animals. Control with frequent mowing, physical removal and application of pre-emergent herbicides in cooler climates. In the south, where they are persist ant all year, apply a contact herbicide for chemical control.
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Burclover (Medicago minima) has clover-like leaves with three leaflets per leaf. It is a creeping plant that spreads by above-ground stolons and appears in the spring before other weeds. It produces yellow flowers followed by the seeds, or burs, that cling to passers-by and pets. It is controlled chemically with a broad leaf or contact weed killer and good cultural practices that create a healthy lawn. Digging up burclover may cause it to spread as each broken section can establish a new plant.
Carpet burweed or lawn burweed (Soliva spp.) is most often seed in lawns during the winter. It is low-growing with soft feathery foliage. In severe infestations, carpet burweed completely covers a lawn. The yellow flowers are small and may not be noticeable, but each plant produces one large hard burs in the middle of the plant. The burs are very sharp and remain viable after the plant dies. They attach themselves to shoes and pets allowing the plant to spread to other areas. Control carpet burweed with a broad-leaf herbicide applied while it is actively growing in the fall and spring or mechanical control.
Puncturevine, or goatheads (Tribulus terrestris) is a spreading annual with compound leaves and yellow flowers. It is found in disturbed areas and lawns throughout the southwest. Puncturevine has a taproot and thrives in poor dry soils. Growth radiates from the center of the plant outward to 5 feet in diameter. The burs are very hard once mature and can puncture shoes, animal hoofs and tires. Control of puncturevine is established with pre-emergent herbicides and mechanical control.