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 broad leaf weed, an annual, or a
perennial. Most turf weeds belong to two
principal categories – grasses and broad leaf 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 pre-emergent 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. Pre-emergent
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 post-emergent herbicide during its
season of active growth. Products such
as Portrait, Amaze and Dimension are available locally and need watering in
order to activate.
Effective
chemical weed control requires identification of the weeds as to their
Classification (grass, broad leaf, 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.
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