Crabgrass is an annual weed that invades lawns throughout the United States. According to Purdue University, crabgrass seeds germinate when soil temperatures are above 60 degrees Fahrenheit for three to five days. Crabgrass can be controlled by liquid herbicides, available in both pre-emergence and post-emergence formulas.
According to Grounds Maintenance, pre-emergent herbicides provide a chemical barrier on the lawns that prevents crabgrass seeds from germinating. These chemicals come in single-season and multiple-applications types.
Post-emergence herbicides are applied after crabgrass begins to emerge in the lawn, according to American Lawns. Generally, lawn care maintenance officials use a pre-emergence and a post-emergence herbicides to properly treat a crabgrass infestation.
Horticultural researchers often debate over when herbicides should be applied to the lawn. Generally, crabgrass begins to grow in the spring. As a result, lawn maintenance officials typically apply pre-emergence herbicides just weeks before the ground warms enough for crabgrass to begin to appear. Others feel it is best to apply pre-emergence herbicides in the early fall, as the ground cools and grasses go dormant for the winter. According to Grounds Maintenance, both procedures are effective, provided the chemicals are properly applied.
Pre-emergence herbicides should be applied according to the directions on the product. There are two main types of pre-emergence herbicides. According to Ground Maintenance, single-season-application varieties can be applied in the early fall or early spring by spraying the liquid herbicide directly on the grass. It's important to spray as close to the soil line as possible. Products that need multiple applications throughout the growing season, every six to eight weeks, are applied in the same manner. Post-emergence herbicides are applied by spraying the lawn with a fine mist after crabgrass has begun to appear, according to American Lawns.
According to Grounds Maintenance, there are several factors that limit the effectiveness of a liquid crabgrass-control method. Microorganisms that live in thatch and in the soil can degrade chemicals. Through a process known as photodegradation, sunlight also breaks down the chemicals used in liquid herbicides. Therefore, it is important for a homeowner to keep an eye on his lawn and use a post-emergence crabgrass treatment if necessary.
- Photo Credit grass image by Brett Bouwer from Fotolia.com
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