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Preemergent herbicides are a form of chemical weed control which prevent germinated weed seedlings from becoming established.
In some areas of the world, they are used to prevent crabgrass from appearing in lawns.[1] Preemergent herbicides are applied to lawns in the spring and autumn, to prevent the establishment of weed seeds. They will not affect any established plant. In the spring, they should be applied when air temperatures reach 65–70 °F for four consecutive days. In the autumn, they should be applied when nighttime lows reach 55–60 °F for four consecutive nights.[2]
"Weed and feed" products which contain both preemergent herbicide and fertilizer in a single product should not be used on southern lawns or warm-season grasses. If applied when preemergent herbicide is needed, the fertilizer may burn or stress the lawn. If applied after the lawn "green-up", weed seeds will have already germinated and the herbicide will be ineffective.[3] Preemergants do not prevent seeds from germinating, they prevent cell division, and prevent vital parts of the weed from forming
- ^ Wright, Robert (April 20, 2010). "The Dandelion King". New York Times. Retrieved 2010-04-21.
- ^ Williamson, Joey. "Managing Weeds in Warm-Season Lawns".
- ^ Tyson, Jenion. "When to apply preemergent herbicides".