By Richard L. Duble, Turfgrass Specialist (Retired)
Texas Agricultural Extension Service
Copyright © Richard L. Duble
Aggressive competitors for sunlight, moisture, and nutrients and prolific multipliers even under adverse conditions, weeds present a challenge for even the most experienced turfgrass managers. The color, texture, and growth rate of weeds often contrast markedly to those of the turfgrasses they may be associated with in a lawn or sports field. Consequently, weeds detract from the uniformity of a turf and add to its maintenance requirements.
The origins of weeds are as varied as those of our turfgrasses. Most are introduced species from Asia and Europe that were inadvertently brought to this country. Many were unintentional stowaways in animal fodder or ship ballasts, or simply contaminants in seed or food supplies brought to this country.
In lawns and sports fields, weeds are often the result of poor quality turf, rather than the cause of poor turf. The aggressive nature of weeds and their prolific reproductive capacity enable them to invade thin, weak turf areas. Cultural practices should always be viewed as the first step to effective weed control. Always determine why weeds established a foothold and correct those deficiencies. If the basic problem is not corrected, weeds will continue to occur. An effective weed-control program also requires identification of the undesirable species as to its classification as a grassy weed, a broadleaf weed, an annual, or a perennial. Most turf weeds belong to two principal categories - grasses and broadleaf plants. Chemical controls for these two categories of plants frequently differ.
Grassy weeds have jointed, hollow stems; leaf blades have veins parallel to leaf margins, and are several times longer than they are wide; roots are fibrous and multi-branching; and flowers are usually inconspicuous. In contrast, broadleaved plants often have showy flowers; leaves have a network of veins at diverse angles to one another; stems are often pithy; and a taproot is usually present. Another group of turf weeds, sedges, have grasslike characteristics, but require a different group of chemicals for control. Sedges are characterized by three-sided stems (triangular cross-section) which bear leaves in three directions (in contrast to the two-ranked arrangement of grass leaves).
Weeds can be further grouped according to their life span - annual or perennial. From the standpoint of chemical control, the grouping is most important, because preemergent herbicides are only effective for control of annual weeds. Annual weeds germinate from seed each year, mature in one growing season, and die in less than 12 months. Crabgrass and henbit are examples of annual weeds - crabgrass being a summer annual and henbit being a winter annual. Preemergent herbicides must be applied according to the expected date of emergence for each targeted species.
Perennial weeds live more than one year, and recover or regrow from dormant stolons, rhizomes, or tubers as well as from seed. Control of perennial weeds requires a postemergent herbicide during its season of active growth.
Effective chemical weed control requires identification of the weeds as to their classification (grass, broadleaf, sedge, etc.), life span (annual or perennial), and season of active growth (cool season or warm season). Effective chemical control also requires accurate timing of applications, proper rate of application, and uniformity of application. Always follow label directions for a product, and observe all warnings and precautions relative to safety of the application. Herbicide labels should be carefully reviewed for additional details on specific uses of each product.soil and sunny locations.
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