Answer: I think you're right. Crabgrass has smaller leaf blades than St. Augustine and is jointed at shorter increments. The stems are narrow with opposite leaf blades. Crabgrass spreads quickly during the warm summer months. Between midsummer and early fall, each plant produces thousands of seeds. The first frost kills the plants, but the seeds remain dormant through the winter. When the ground temperature warms up, the seeds begin to grow. New crabgrass appears from mid-spring to midsummer. The key to crabgrass control is making sure the seeds cannot germinate. Usually a thick healthy lawn will crowd out crabgrass. But if crabgrass has become established in your lawn, proper lawn maintenance alone may not be enough. Continue to hand pull the weeds this summer and use a pre-emergent herbicide during the late winter or early spring of the next year to prevent any crabgrass seeds left behind from developing at their next opportunity. Pre-emergent herbicides work by killing the crabgrass seedlings as they germinate.
Timing is essential when using pre-emergent herbicides. Application times depend a great deal on weather patterns, which vary from region to region. If your area has experienced a warmer than usual winter, you'll probably need to apply the herbicide earlier than usual.
Apply the herbicide when the ground temperature rises above 60 degrees. Since it's difficult for most of us to monitor the soil temperature, there's an easier way. When you notice shrubs blooming and trees budding, it's time to apply the herbicide. Warm nights and periods of rainfall encourage crabgrass germination. If your weather fits this pattern, get the herbicide in place right away.
Best wishes with your lawn.
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