This month we are addressing a pesky weed, Crabgrass. The two most common species of crabgrass in North America are large (or hairy) crabgrass (Digitaria sanguinalis) and smooth crabgrass (Digitaria ischaemum). They are native to Europe and Eurasia and were introduced to the United States in 1849 as a forage crop. Both are now found across the U.S., in Canada, and almost worldwide. The main difference between them is the presence or absence of hairs on the leaf sheath.
These crabgrasses are summer annuals and are common grassy weeds in turf and landscaping. One plant can produce many tillers (branches or stems) that spread from its center. They can survive mowing as low as ½ an inch and still produce seeds. The seeds remain dormant unless the soil temperature reaches 55°F for four to five consecutive days, then they germinate.
Crabgrass can be selectively controlled with preemergent or post-emergent herbicides. The best time for preemergent application is when the soil temperature reaches 55°F for four to five consecutive days in the spring. Postemergent application is best when crabgrass is in the two- to five-leaf stage. They can still be controlled up until the 2-tiller stage. Complete control becomes increasingly difficult as more tillers are produced and convert to suppression after seven tillers.
