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The best weed control is a healthy lawn. However, some
weeds are invasive and compete well with lawns. Weed control
should be practiced only on established lawns. Young seedlings are
often injured by weed control agents, even when the control agent
is for broadleaf weeds. |
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Weed control requires knowledge about the weed itself.
This includes proper identification and knowledge of the life
cycle of the weed. The idea is to control the weed at its weakest
point in the life cycle. |
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The four terms you should be aware of as Master
Gardeners are selectivity, tolerance, pre-emergence
and post emergence. |
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Selectivity is ability of a weed control agent to
affect one plant (the weed) and not affect another (lawn grass).
Non-selective weed control agents kill all plants (weeds and
turf). Pre-emerge agents kill seeds as they germinate, while post
emergent weed control agents control weeds already established. |
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Pre-emergence weed control agents are used in the fall
and spring at lower elevations and in the spring at high elevation
sites. They are used (on established turfs) in the fall to control
winter annual weeds. These include annual bluegrass, winter
bromegrass, wild barley and other grassy weeds. They are also used
in the spring (and early summer at high elevations) to control
grassy weeds like crabgrass, southwest cupgrass, goosegrass,
stinkgrass and summer annual broadleaves, like spurge and
knotweeds. |
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Most annual broadleaf plants are not controlled by most
of the pre-emergence control agents which control grassy weeds.
There is one herbicide that works well on broadleaf weed seeds. It
is called "Gallery." It will stop turf seeds from coming
up at the same time (as most other pre-emergence agents will do). |
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Broadleaf perennial weeds (live year-round) include
dandelions, white clover, medic, thistles and the like. Broadleaf
perennials should be controlled by fall applications of broadleaf
weed control agents. The second choice, is an application in the
spring. |
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Other weeds include the sedges. Purple nutsedge is
prevalent at mid-to-lower elevations, while yellow nutsedge is
prevalent at higher elevations. Nutsedge is not a grass, although
it is falsely called nutgrass by most people. Selective herbicides
are now available for its suppression. |
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Finally, non-selective weed control agents can be used
to spot spray weeds in the turf. These will kill all weeds,
including the turf, so care must be exercised. Examples include "Round-up,"
and the new herbicide "Finale." |
