There are basically two times per year to apply a preemergence herbicide when attempting to prevent annual weeds in a lawn. This is February when targeting summer annual weeds such as crabgrass and Florida pusley and October when targeting winter annual weeds such as chickweed and annual bluegrass.
First, if you called to request the factsheets on summer and winter annual lawn weed control and could not get our office, please call again. Unfortunately, we were having problems with our phones. The problems have been fixed. The factsheets include a list of preemergence herbicide products.
Secondly, below includes additional information based on questions generated from last week’s article,
There are basically two times per year to apply a preemergence herbicide when attempting to prevent annual weeds in a lawn. This is February when targeting summer annual weeds such as crabgrass and Florida pusley and October when targeting winter annual weeds such as chickweed and annual bluegrass.
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The main reason to use a preemergence herbicide now is if your lawn has had a history of problems with summer annul weeds. Summer annual weeds don’t exist now. They are in the form of seeds now, which were produced from last summer’s crop of summer annual weeds. So if you had summer annual weeds growing in your lawn last summer, you’ll have thousands of seeds waiting to germinate as soon as we move into the warmer days of spring.
Then, they’ll start the next generation that will grow and produce their own seeds during late spring through fall. With the first killing frost or freeze later in 2019, the parent plants will be killed but the countless number of seeds they produced will survive the winter only to germinate the following spring of 2020 to start the cycle again. The best way to break this cycle is to apply a preemergence herbicide in February to prevent the next generation from emerging.
When applied correctly, preemergence herbicides form a chemical barrier (layer) along the soil surface that inhibits or kills weed seedlings as they come in contact with this layer. The weed seeds germinate and are controlled as they emerge and come in contact with the herbicide. It’s important to not disturb this chemical barrier after applying the herbicide. Raking the yard, mowing the yard or even walking through the lawn after applying the herbicide could disturb the thin herbicide layer/barrier resulting in ineffective control in those disturbed areas.
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For best results with controlling summer annual weeds, apply the preemergence herbicide in February when day temperatures reach 65°to 70°F for 4 to 5 consecutive days. This will be just before the summer annual weeds emerge.
For season-long weed control, a second application of preemergence herbicide may be needed 6 to 9 weeks after the initial application, based on the product’s label directions.
Follow all label directions and precautions when using any pesticide, including herbicides!
Larry Williams is the Extension horticulture agent with the Okaloosa County Cooperative Extension Service, University of Florida. Contact Larry at 689-5850 or email lwilliams@myokaloosa.com.
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