Institute of Food and Agricultural Sciences
Hendry County Horticulture News
Lawn Weed Primer
The proper identification and an understanding of growth habits of lawn weeds are important in understanding the biology and best control strategy.
The first and best method of weed control begins with proper management to encourage a dense, thriving turf. Healthy turf shades the soil so sunlight can't reach germinating weed seeds. A thick turf will also minimizes the physical space available for weeds to become established. There are several things to consider when attempting to grow healthy grass.
The first is whether the best turf species or variety is being grown for a particular area. For example, areas heavily shaded will support only a few grass species. Growing bermudagrass or bahiagrass under any shade will result in thin, weak turf which is susceptible to weed invasion. Choices for shady conditions would include specific cultivars of zoysiagrass or St. Augustine.
Proper fertilizing, watering, mowing, and other pest control measures will help to produce desirable turf. Turf, that is over watered and fertilized or mowed too low or too infrequently, will be weak and unable to compete weeds.
Turf damaged by foot or vehicle traffic invites weeds. Turf compacted by excess traffic, especially when the soil is water saturated, cannot obtain adequate oxygen and will suffer. Goosegrass, and certain sedges will thrive in compacted and/or continuously wet soil.
Turf damaged by insect pests may not always recuperate quickly enough to out compete germinating weeds. Tunneling from mole crickets disrupts the soil surface, enabling weed seeds to readily germinate and become established. Other insects and diseases can cause large bare patches. These open areas will enable weeds to become established.
Areas adjacent to lawn areas which are hard to mow such as fence rows or ditch banks often support a weed population, which will produce seed and infest nearby turf. These areas should receive some weed control. Good sanitation practices should be followed, such as planting only certified seed, using weed free sod, and the practice of washing off mowers used in weed infested areas before mowing in weed free areas.
Knowledge of weed life cycles is an important part of successful weed control. Weeds may complete their life cycles in either one growing season (annuals), two growing seasons (biennials), or three or more years (perennials). Annuals that complete their life cycles from spring to fall are referred to as summer annuals, and those that complete their life cycles from fall to spring are winter annuals. Summer annual grasses, as a class, are the most troublesome weeds in turf.
Weeds can also be classified by their botanical characteristics and may be divided into broadleaves, grasses, rushes and sedges. Broadleaves, or dicotyledonous plants, have net-like veins in their true leaves and usually have showy flowers. Examples include chickweed, Florida pusley, beggarweed, matchweed, and many others.
Grasses are monocotyledonous plants that have only one seed leaf when seedlings emerge from the soil. Grasses have hollow, rounded stems with nodes (joints), and parallel leaf veins. Examples include crabgrass, goosegrass, cogongrass, torpedograss, and smutgrass.
Sedges have stems which are triangular shaped and solid while rushes have solid round stems. Both favor a moist habitat. Economically important members include yellow and purple nutsedge as well as annual, and water sedges, path and beak rush and perennial kyllinga.
If weeds become established in turf there are several methods of control are available. Proper mowing height and frequency will help eliminate many annual weeds. Mowing prior to weed seed head formation will also help reduce weed seed reserves.
When only a few weeds are present, it may be easiest to physically remove the plant, but if weeds are a major problem, other alternatives should be considered. Use of mulches and other material to exclude light and smother weeds is effective in certain areas, such as flower beds, foot paths, or nurseries, where turf is not grown.
Herbicides may also be used to effectively control many lawn weeds. A herbicide is any chemical which injures or kills a plant. Herbicides are safe and effective if product label instructions are followed. Label instructions include proper timing of application, proper rates, and dispersal methods. Timing of herbicide application during the plant's growth cycle also is important. For example, weeds not controlled prior to seed head formation are harder to control and are able to deposit new seeds for future problems.
Good luck and good gardening.
Gene McAvoy is the horticulture agent with the Hendry County Extension Service. Direct your horticulture questions to PO Box 68, LaBelle, FL 33975, e-mail - firstname.lastname@example.org or phone 863-674-4092 or 863-983-1598. You are also welcome to visit the Hendry County Extension Office at 225 Pratt Blvd., LaBelle. Office hours are from 8:00 - 5:00.
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