What Kills Annual Bluegrass?
Annual bluegrass (Poa annua) is a cool-season, grassy weed infesting lawns. This weed competes with turf grass for nutrients, sunlight and air. Annual bluegrass ruins the turf's uniform look. Kill existing annual bluegrass and take preventative measures against its recurrence. Does this Spark an idea?
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Identification
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Annual bluegrass weeds pop up within lawns in the late summer to early fall, according to Purdue University Turfgrass Science and Department of Agronomy. Because perennial bluegrass resembles annual bluegrass, it is hard to distinguish between them. Look for grassy areas displaying an upright growth characteristic for annual bluegrass, according to the University of California. Perennial bluegrass grows lower to the ground than annual bluegrass. Annual bluegrass survives low mowing better than other types of bluegrass, such as Kentucky bluegrass.
Post-Emergent Herbicide
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Do not mow the lawn for two days before spraying. Vigorously growing annual bluegrass is easier to kill with post-emergent herbicide. Spray annual bluegrass growing within Kentucky bluegrass, perennial bluegrass and Bermudagrass with an herbicide containing ethofumesate, as suggested by the University of California. Kill annual bluegrass growing in warm-season turf types with post-emergent sprays containing pronamide. It takes 15 to 20 days for pronamide to kill annual bluegrass.
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Pre-Emergent Herbicide
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Pre-emergent herbicide prevents annual bluegrass seeds from germinating. Apply pre-emergent sprays before annual bluegrass germinates in the late summer. Annual bluegrass seeds need temperatures below 70 degrees to germinate, according to Purdue University. Check the soil in the late summer with a soil thermometer when the soil temperatures start to dip. Spray a pre-emergent herbicide containing benefin, bensulide, DCPA, dithiopyr, oxadiazon, pendimethalin or prodiamine, as suggested by the University of California.
Treatment in Flowerbeds
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Annual bluegrass invades garden beds. Unfortunately, few herbicides are effective for controlling these grassy weeds among ornamental plants, according to the University of California. Gardeners should dig up weeds and replant areas. Keep weeds from the lawn from invading garden beds with mulch around the plants. Spread a 2- to 3-inch layer of organic or synthetic mulch types 2 inches away from the plant's base.
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