Large Crabgrass

Biology

In the Midwest, species like Large, Smooth, and Southern crabgrass are common and collectively known as crabgrass. These species often rank as the most problematic weeds in lawns. In the Midwest, crabgrass typically starts germinating in April, with earlier germination in southern areas (late March) and later in northern areas (late April). You can track its germination using the germination tracker at www.gddtracker.net.

Identification

It’s a common lawn weed, thrives in hot, dry conditions. Actively maintain your lawn to prevent its spread. Regular mowing, for example, effectively limits its growth. Additionally, ensure proper fertilization, as a well-nourished lawn resists weeds better. Furthermore, consider aerating the soil; this prevents compaction, a condition favorable for this grass type. In cases of severe infestation, selective herbicides can be useful. Remember, consistent lawn care is key to controlling crabgrass.”

Cultural control

Proper mowing (higher mowing heights), proper fertilization (some rather than none to improve turf density), irrigation to prevent summer dormancy during drought, and aerification of compacted areas to improve turf health are all cultural practices that can be used to reduce crabgrass.

Biological control

Some organic herbicides are available. The predominant organic herbicide in turfgrass systems is corn gluten meal for preemergence control. This product has shown to be effective in northern states in lawns, although tests in Indiana and states south of Indiana show it has limited efficacy on crabgrass and that encouraging a dense turf through proper mowing, irrigation, and fertilization is equally effective.

Chemical control

It can be controlled using preemergence or postemergence products.

Dithiopyr (Dimension), pendimethalin (Pendulum), and prodiamine (Barricade) are common ingredients in preemergence products. These herbicides inhibit cell division and prevent crabgrass seeds from properly emerging. Since these herbicides work on germinating seeds, you must apply them prior to germination — with the exception of dithiopyr, which controls it after germination until it reaches one tiller.

Another approach to controlling it is to use postemergence herbicides after the grass has already emerged. Dithiopyr, quinclorac (Drive and others), MSMA (sod and golf), mesotrione (Tenacity), Fenoxaprop (Acclaim Extra) and other herbicides containing these ingredients can be used for postemergence crabgrass control. Each of these ingredients offers a slightly different spectrum of activity and works on specific sizes of grass. Pick one based on the size of the grass you’re treating and the other weeds you have present in the area.