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LAWNS: MAINTENANCE [continued]

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  MG Manual Reference
Ch. 12, pp. 43 - 44

[Maintenance: irrigation | new lawn | fertilization | renovating | mowing | mowing heights
| dethatching | aeration | weed ]

WEED CONTROLTop

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.
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.
The four terms you should be aware of as Master Gardeners are selectivity, tolerance, pre-emergence and post emergence.
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.
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.
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).
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.
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.
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."


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