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Scott’s Halts Crabgrass Preventer is a pre-emergence herbicide that contains the active ingredient pendimethalin, which is a crystal-like man-made chemical that is used in a variety of herbicide products. Scott’s Halts Crabgrass Preventer stops the growth of both summer and annual weeds before they have a chance to germinate and establish themselves in your lawn. Preemergence treatments are considered more effective for crabgrass control, and they also are less likely to injure your grass, according to Michigan State University.
The general rule is to apply pre-emergence herbicides when the soil temperatures warm in the spring to at least 50 or 55 degrees Fahrenheit. This is before the grass begins to grow, and therefore allows the herbicide to create a barrier before the crabgrass begins to grow. Note that established crabgrass are not affected by pre-emergent herbicides, as they work only before germination begins.
The application schedule for Scott’s Halts Crabgrass Preventer depends on the type of weed you’re trying to control, according to Scotts.
March to May
To prevent crabgrass (Digitaria spp.), and other spring annual weeds such as spurge (Euphorbia spp.), foxtail (Setaria spp.) and yellow woodsorrel (Oxalis spp.), Scott’s Halts Crabgrass Preventer should be applied in early spring. The key to successful control is to treat the soil before the weed you’re trying to control begins to germinate. In Northern California, for example, Scott’s says to apply the product before mid-March. While crabgrass typically germinates in early May, other spring weeds may germinate at different times, but pre-emergent control of most spring weeds is typically successful when herbicides are applied before outdoor temperatures begin to average 80 degrees Fahrenheit.
August to October
Winter weeds typically germinate in the late summer to early fall, but remain dormant and resume growth when temperatures become warm again. To prevent the germination of these weeds, apply Scott’s Halts Crabgrass Preventer between August and October. Winter weeds controlled by Scott’s Halts Crabgrass Preventer include annual bluegrass (Poa annua), henbit (Lamium amplexicaule), and chickweed (Stellaria media).
