Home Lawn and Turf in Mississippi
To maintain an attractive lawn, you have to learn to manage weeds. Weed control in a lawn begins with a healthy, vigorous, dense stand of turf. Healthy turf helps control weeds by growing to fill bare areas, shading the soil surface, and shading newly emerged weed seedlings. Without sunlight, many weed seedlings cannot survive. An attractive, weed-free lawn can bring a sense of satisfaction and accomplishment to the homeowner.
Weed identification is the first step toward chemical control. The pest must be correctly identified before a herbicide to control it can be selected or recommended. County Extension agents can assist you with weed identification. Several inexpensive identification guides are available at most bookstores. Most of these guides contain color photographs as well as written descriptions.
Lawn weeds can be grouped into one of three broad classes: grasses, sedges, or broadleafs. Grasses and sedges are similar with their long, narrow leaves and parallel veins. Grasses, however, have solid nodes (joints) and hollow internodes, and sedges do not. Sedges also have leaves arranged in threes. Hence, a cross-section of a sedge stem appears triangular. Broadleaf weeds have showy flowers and leaf veins in a net arrangement.
Weeds can be further classed into three broad categories based on their life cycles.
Annuals are those weeds that produce seeds within 1 year after emergence. Those that emerge in the spring, grow through the summer, and produce seeds in the fall are called summer annuals. Examples of summer annuals are crabgrass, goosegrass, spurge, knotweed, and annual lespedeza. Weeds that emerge in the fall, grow in the winter, and produce seeds in the late spring are called winter annuals. Examples of winter annual weeds are henbit, chickweed, and annual bluegrass.
Biennial weeds require 2 years to produce seeds. These weeds emerge and grow the first year, overwinter as a dormant rosette of leaves, resume growth, and produce seeds the second year. Wild carrot and common mullein are examples of biennial weeds.
Perennial weeds emerge, grow, and produce some structure that enables the plant to overwinter and resume growth year after year. These plants typically reproduce by vegetative mechanisms as well as seeds. Common examples are bermudagrass, bahiagrass, dallisgrass, Florida betony, Virginia buttonweed, wild garlic, and nutsedge.
Perennial weeds reproduce by several vegetative structures. Bermudagrass produces rhizomes, or underground stems, capable of rooting and producing new plants at each node. Bermudagrass also produces stolons that are similar to rhizomes but are above the soil surface rather than below. Yellow and purple nutsedges produce tubers (or underground storage organs) capable of producing new plants. A potato is an example of a tuber. Wild onion and garlic produce bulbs or underground vertical stems encased in fleshy leaves. The other mechanism of vegetative reproduction is creeping roots or roots modified for food storage and reproduction. This reproductive mechanism is used by Virginia buttonweed.
Most of the recommended turf-production practices, although not solely intended as weed control methods, do help control weeds. All production practices that promote healthy turf also help reduce weed establishment. This includes use of soil tests to maintain recommended pH, timely addition of recommended rates of fertilizer, controlled irrigation during periods of limited rainfall, insects and disease management, and proper mowing.
Although these practices are considered standard agronomic production tips, they can also help control weeds. As environmentalists, we must manage the turf to use its competitive ability to help control weeds.
Bare soil is a prime area for weed invasion. Bare areas should be reseeded, plugged, or left for adjacent grass to grow into. Areas reseeded or left void should be covered with mulch, such as grain straw, until turf fills the area.
Regardless of how well you manage the turf, weed seed germinate and seedlings emerge. You should rely on other control methods when this occurs.
Some scattered, individual weeds (wild garlic, for example) can be removed by hand. However, hand removal is a tedious and time-consuming process. Herbicides that will reduce the time required to control weeds are available.
Chemical Weed Control
Herbicides can be divided into two groups: selective and nonselective.
Selective herbicides injure some plants but not others. For example, 2,4-D controls many broadleaf weeds, but does not injure bermudagrass. If, however, you use an excessive rate on a sensitive hybrid bermudagrass, injury will probably occur. Warning: Selective than the label recommends. Use caution to apply the rate stated on the product label.
Nonselective herbicides control or injure all plants that are contacted with the spray solution. These herbicides are useful to control all vegetation before lawn renovation or to control emerged weeds in driveways, sidewalks, and patios. Roundup is an example of a nonselective herbicide.
Herbicides can also be classified by their method of application: preemergence and postemergence.
Preemergence herbicides are applied to the soil surface or turf canopy before weed emergence. These herbicides kill weeds before or soon after seedling emergence. Chemical weed control begins with a preemergence herbicide application. If you do not use a preemergence herbicide, weed control becomes a defensive tactic. Apply preemergence herbicides from February to mid-March to control summer annual weeds.
For winter annual weeds, apply after mid-August and before September 1. Individuals in the southern part of the state should apply preemergence herbicides at the beginning of this time and those in the northern part of the state at the end of this period for summer annuals, and reverse these timings for winter annuals.
All preemergence herbicides must move into the upper portion of the soil to control weeds. Herbicides not washed into the soil are decomposed by ultraviolet sunlight or lost as vapors. Some herbicides are more susceptible to decomposition than others. Therefore, the length of time varies that a herbicide can stay on the soil surface before moving into the soil and still provide acceptable weed control. However, the sooner after application the herbicide is washed into the soil, the better the weed control will be. Rainfall will move these materials into the soil, but if rainfall is not forecast within 1 or 2 days after you apply a preemergence herbicide, you should water a half-inch to move the herbicide into the soil.
Postemergence herbicides are applied after weed seedling emergence (no application window is stated). Carefully examine your lawn for the invasion of weed seedlings that were not controlled by the preemergence herbicide.
Postemergence herbicides are most effective if applied to seedlings less than 3 inches tall. Wait until most weeds are 2 to 4 inches tall. Since weed seedling emergence occurs for several weeks, more than one application is needed to control weeds the entire season.
Herbicides are available in several formulations: emulsifiable concentrate (EC or E), water dispersible (WDG, D, DF), flowable (F, AS, LF), soluble concentrate (S), soluble powder (SP), or microencapsulated (M or ME). These formulations are mixed with water and sprayed onto the turf canopy or weeds. All formulations contain inert ingredients in addition to the active herbicide ingredient (active ingredient or ai). They also contain emulsifiers, surfactants, wetting agents, or antifoaming agents that help keep the active ingredient suspended in water and enhance plant uptake. All herbicide labels state the amount of active ingredient and amount of inert ingredients in the container. Knowledge of this information can help you make economical herbicide purchases.
Other herbicides are available in granular formulations (G). The granules are applied directly to the turf or soil surface. Granular materials may be less difficult to apply but are more expensive per unit of active ingredient than the sprayable formulations. Many herbicides are available in sprayable or granular form.
Activity of most postemergence herbicides is enhanced with addition of an adjuvant (or surfactant). Some herbicides require use of surfactant. Adjuvants facilitate herbicide movement into the leaf. Many types of adjuvants are available, and the concentration of active ingredient varies among brands. For most turf herbicide applications, a nonionic surfactant with at least 85 percent active ingredient is sufficient.
The adjuvant rate to add to the tank is stated on the herbicide label. Most, however, recommend 0.25 percent based on the volume of the spray tank (indicated v/v). If, for example, the volume of a spray tank is 1 gallon (or 128 ounces), and the label recommends addition of 0.25 percent (v/v) surfactant, 0.3 ounces surfactant should be added to the spray tank.
Some individuals suggest household detergents can be substituted for surfactant. This is not recommended for several reasons. Household detergents do not contain as much surface active ingredient per unit volume as do agricultural surfactants. The amount of surface active ingredient per unit volume varies among brands of detergents. Hence, their use is more costly than use of agricultural surfactant. Detergents foam excessively, can form scums that affect sprayer performance, and can interfere with herbicide activity. Remember to purchase a good agricultural surfactant, if the label recommends its use, to save money.
Many preemergence and postemergence herbicides are labeled for use in Mississippi lawns. A visit to the local cooperative dealer or garden center confirms this statement. Don’t purchase a herbicide without serious consideration. Determine the type of turf in your lawn and the weeds that are present or anticipated. Then determine which herbicide(s) will provide the best control of the weeds in your turf.
Some weeds are more easily controlled with preemergence herbicides than with postemergence herbicides. For this reason, a combination of preemergence and postemergence herbicides may be necessary for year-round weed management in most lawns.
Turfs vary in their sensitivity to herbicides. Table 11 contains a listing of turfgrass tolerance to herbicides.
Consult this table before you make the final herbicide selection. Tables 12 and 13 list weed response to preemergence and postemergence herbicides. These tables are useful to determine which herbicide(s) best controls the weeds present.
Not all herbicides listed in the tables are labled for home lawns. Many of the products listed will injure desirable, broadleaf plants such as trees, shrubs, flowers, and vegetables. Use caution when applying these materials to turf near these plants. Remember, before using any pesticide, read and follow directions and precautions stated on the label.