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DEALING WITH DANDELIONS, CRABGRASS AND CREEPING CHARLIE
Dandelions, crabgrass and creeping charlie are summertime guests that most lawn lovers love to hate. Many of us vow each growing season: "Next year I will do things right and eliminate these scourges from my lawn."
Well, if this was your pledge last summer, it's almost time to start doing things right.
Before heading to the nearest garden center and filling your cart with chemicals, however, consider that an increasing number of weeds in the lawn is often the result of poor grass growth. Causes for poor grass growth include increased shade, lack of soil nutrients, poor watering practices, soil compaction from excess lawn traffic, and mowing too close. Correcting one or more of these conditions is a good place to start your fight against weeds. "The first step in any lawn weed control program is to maintain a thick turf that can choke out most weed problems," says Bob Mugaas, University of Minnesota extension turf specialist.
Mugaas suggests that if only a few weedy plants are present, they should be dug or cut out. Continued removal of dandelion tops eventually reduces reserves in the taproot, which causes the plant to stop growing.
Broadleaf weeds such as dandelions, spurge and creeping charlie may require the use of a broadleaf herbicide or plant killer. Be sure the selected product is labeled for the weeds to be controlled. Follow the directions and heed statements about safety to grass, nearby plants, your health and the environment.
Annual weeds such as prostrate spurge, oxalis purslane and chickweek should be treated in the spring. Biennial and perennial weeds such as dandelions, plaintain, curly dock and thistles should be treated during cooler times when actively growing, usually in September or May.
When applying the labeled herbicide, treat only individual plants or weed-infested areas. General broadcast applications over the entire lawn are wasteful, Mugaas says. Most broadleaf weed killers should be used when the temperature is between 70 and 85 degrees. Avoid their use during the hot dry periods of July and August.
Dry granular herbicides should be applied to wet grass and weeds. Liquid applications should be done on calm days to avoid drift. Avoid watering for at least 24 hours after application to allow the product to dry onto the plant.
Crabgrass is a warm-season annual grass that grows best in the heat of mid-summer. It over-winters as seed, comes up about mid-May or later, and is killed by fall frosts. Crabgrass is not shade tolerant and grows best in full, hot sun.
As with broadleaf weeds, Mugaas says a healthy, relatively dense lawn is the best defense against crabgrass. Properly fertilizing and watering your lawn will help ensure an adequate supply of plant nutrients and water for vigorous grass growth.
Second, adjusting mower height upward will provide more shade at the soil surface. Without adequate light, crabgrass seeds, along with some other weed seeds, will not germinate as readily, if at all. Most home lawns can be mowed at 2 1/2 to 3 inches.
Third, a "pre-emergent" weed killer can be used to destroy crabgrass seeds as they germinate, before they emerge from the soil. Apply pre-emergents from late April to mid-May. Crabgrass is likely to be more of a problem weed in warmer areas adjacent to curbs, driveways and sidewalks. It may only be necessary to apply a pre-emergent herbicide in those areas.
One application put down at the proper time gives season-long control, Mugaas says. If an application is made very early in the season, a second application may be necessary during mid- to late June. Always follow pre-emergent herbicide applications with one-quarter to one-half inch of water. This helps move the herbicide to the soil surface where it provides the control.
Post-emergent herbicides for crabgrass are usually not recommended, Mugaas says, and are only effective when plants are very small.
In lawns heavily infested with creeping charlie, Mugaas recommends using a de-thatching machine, vertical mower or power rake. These tools comb through the grass, pulling much of the weed out. It doesn't eliminate it, but keeps it in check. The best time for these operations is between mid-August and mid-September.
If lawns where creeping charlie is the dominant plant, you may wish to start over. Apply glyphosate (a nonselective herbicide, sold as Monsanto Roundup or Ortho Kleenup) to kill the entire area. Then you can re-seed with grass varieties more tolerant of the conditions.
Creeping charlie can be controlled chemically by applying a herbicide containing the active ingredients 2, 4-D and MCPP. Spray as soon as the weed is growing actively in spring. However, fall applications may be more effective. Temperatures should be in the 60's, 70's, or low 80's with no rain forecast for 48 hours. Read label carefully and spray only when it's not windy to avoid herbicide drift onto desirable plants.
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