Crabgrass (Digitaria, D. sanguinalis) runs rampant throughout the United States. Crabgrass germinates when the ground temperature reaches
a sustained 55 degrees and forms conspicuous, large patchy clumps in lawns, ornamental landscapes, and vegetable gardens. There are as many as 300 different species of Digitaria. The most common forms in the US are smooth crabgrass and large crabgrass.
Smooth and Large Crabgrass
Smooth crabgrass begins to germinate when the ground temperature reaches 55 degrees and if left unmowed, will grow to a height of about 6 inches. But even when mowed low, smooth crabgrass will spread by dropping seed pods that will continue to germinate throughout the season.
Smooth Crabgrass leaves are smooth and 1/4 inch wide by 5 inches long and the light green color makes it stand out in your lawn. Ugly!
Large Crabgrass is a low-growing, summer nuisance that spreads by dropping seed pods and, like smooth crabgrass, if left unchecked will continue to germinate and spread throughout the growing season. Unmowed, it can reach heights of up to two feet, however, it will not tolerate a close mowing. Large crabgrass leaves are light green, hairy and up to five inches long.
Pre- and Post-Emergent Control of Crabgrass
Crabgrass continues to flourish throughout the growing season by immediately dropping seed pods upon emergence. A successful program to eliminate crabgrass requires BOTH a pre-emergent and post-emergent solution. When the constant ground temperature reaches 55 degrees, crabgrass will begin to emerge. Consult our Crabgrass Germination Map for information in your neck of the woods. A pre-emergent solution such as Prodiamine 65 must be applied before the germination process begins. With a barricade of Prodiamine applied at a rate of 2-3 tablespoons per gallon of water for every 1,000 square feet, you will establish a strong first-line of defense that will last for 3-4 months. For complete information, please consult the Prodiamine Label. Please note that Prodiamine, and most pre-emergent solutions are non-selective, which means that both desirable (grass) and undesirable (weeds) seeds will be sterilized as they emerge. Make sure that your lawn is “established” before applying Prodiamine. Once a lawn has been mowed 2-3 times, it is deemed established. While pre-emergent solutions provide a very strong first line of defense, despite your best efforts, some weeds will emerge. Chalk it up to Mother Nature and the wind. When crabgrass has popped through, it’s time to move to your post-emergent game plan. As a general rule, going after young weeds will produce better results than waiting for them to establish and toughen. When the temperature is above 70 degrees, an effective post-emergent product like MSMA 6 Plus can be used to kill crabgrass. Applied at a rate of one ounce to a gallon of water per 1,000 square feet, MSMA will kill crabgrass, dallisgrass, sandburrs and many other tough broadleaf weeds. For a complete kill, two applications should be made, about 15-20 days apart. MSMA 6 Plus contains a surfactant that will help adhere the solution to the crabgrass leaves, and should be applied when the temperature is between 70-95 degrees. Another outstanding solution to control post-emergent crabgrass is Quinclorac 75.