13 common lawn weeds & how to identify them

Flower & Garden Magazine, April-May, 1993 by Patricia Dalton Haragan

Lawns, Like Trees and Shrubs, are a permanent part of the landscape. Nothing is more visually satisfying than a well-manicured, weed-free lawn. It pleasingly reveals the underlying contour of the land and shows off a house or garden. In addition, a lawn performs practical functions: it cools the air in the heat of summer, reduces dust, water and mud problems, and helps buffer noise.

Turfgrasses carpet the ground with green, but unlike groundcovers of pachysandra or English ivy, grass stands up to foot traffic and invites a barefoot stroll on its surface. A well-maintained lawn, luxuriant in growth, also increases property value by providing aesthetic appeal. Weeds, by spoiling the uniform appearance of a lawn, make the landscape look unkempt. Even a minor weed infestation can alter the appearance of an attractive lawn. Thus, if the goal is to have a weed-free lawn, it is in the homeowner's interest to follow a good weed-management program. Weeds are troublesome in lawns because they are extremely aggressive and highly adaptable plants. They may be grasses, grasslike plants or broad-leaf plants; they may be annuals, biennials or perennials. These pests compete with the turfgrass for water, space, nutrients and light.

Weeds are prolific seed producers, and some of these seeds can lie dormant in the soil for years. If the existing grass cover begins to thin or the soil is disturbed, weed seeds are given a chance to germinate. Since weeds grow rapidly, they can quickly form a dense cover in an area and shade out more desirable species. Insects, diseases and severe weather conditions can cause problems in the landscape by weakening the turf, thus providing ideal conditions for weeds to invade. To remedy this situation, it is essential that the homeowner choose an appropriate grass for the climate, maintain good soil moisture and fertility, and mow at the right height and frequency. These steps will produce a dense, vigorous grass cover, which goes a long way toward ensuring a weed-free lawn.

Weed identification goes hand-in-hand with establishing a lawn. When weeds appear, it is important to correctly identify them so that proper control measures can be initiated. Control methods include herbicides (chemical weed killers) and cultural practices such as mowing, hand weeding and hoeing.

Keep in mind that weeds react differently to these methods. For example, dandelions have a deep-seated taproot beneath their ground-hugging rosette of leaves. Mowing simply removes the flower or seed stalks and possibly a few leaves but has no effect on the taproot. The taproot must be killed (or removed in its entirety) in order to eliminate this weed. The more the homeowner learns about a weed's growth habit, the easier it will be to effectively control the weed. Cultural practices for eradicating weeds should be considered before resorting to herbicides. Hand weeding is the oldest method of controlling weeds. It is effective against annual and biennial plants, provided the root system is removed. With perennial weeds, it is best to pull them when they are in the seedling stage because once established, they are difficult to uproot. Even a tiny portion of a dandelion's taproot left in the soil will resprout.

Mowing is another method commonly used to eliminate weeds in lawns. If properly timed, mowing prevents weeds from producing seeds. It is best to mow weeds before they flower -- some may still produce viable seed if they are in bloom as they are cut. Mowing weeds also reduces their leaf area, thus lessening their ability to manufacture energy reserves through photosynthesis. Repeated mowing weakens and finally kills many types of weeds.

Any homeowner who chooses to use herbicides should understand the difference between the two general categories of weed killers: pre-emergence and post-emergence. Pre-emergence herbicides are applied before weed seedlings appear above ground and are effective because they prevent seed germination. They are usually applied in early spring, when the daytime temperatures reach 65 degrees for four days or more. Do not apply them to newly seeded lawns. Grasses must be established for at least two months prior to herbicide application. Preemergence herbicides containing the active ingredient DCPA (dimethyl tetrachloroterephthalate) are often recommended for preventing crabgrass, which is more difficult to control once the plants are growing.

Post-emergence herbicides, such as 2,4-D and MCPP, are recommended when weeds are already up and growing. These herbicides work best on young, actively growing weeds, and are usually applied in spring before weeds have a chance to flower and produce seeds. They kill the plants by coming in contact with their foliage. Since herbicide packaging lists weeds that can be controlled by the product, knowing what weeds are present in the lawn will greatly help in choosing a herbicide. Weed killers are often applied to lawns in a granular form in which the herbicide is combined with a fertilizer. These products can be applied with a broadcast or drop spreader. Liquid formulations of herbicides are sprayed onto the lawn with a hose-end sprayer or pressure sprayer.