Warmer temperatures combined with adequate precipitation will cause crabgrass to germinate soon. Have your ‘preventer’ in place before germination.
For lawns that have experienced crabgrass problems in the past, the best approach for control of this annual weed in the coming year is the timely application of a crabgrass prevention herbicide. In Fairfield County, the time for that timely application is rapidly approaching.
Crabgrass is a summer annual grass that will re-establish itself each year from seed that remains near the soil surface from last year’s crabgrass crop. The seed of crabgrass begins to germinate in areas of a lawn where light can penetrate to the soil surface and the soil temperatures warm to nighttime minimum temperatures of 52 – 54 F for at least 5 consecutive nights under conditions of moist soils.
The OSU CFAES Weather System tells us that on March 21, the average 2 inch depth soil temperature in Columbus was 48.9 degrees. Should air temperatures remain near normal in the coming days, we would expect soil temperatures to warm to the point that with continued timely precipitation, crabgrass will begin to germinate in early April.
When applied in a timely fashion, preemergence herbicides can effectively control the germination of crabgrass. A “timely” application requires the herbicide be applied and rained into the soil’s surface before soil temperatures are such that germination can occur. After application of a crabgrass or annual grass preventer herbicide, if above normal precipitation is experienced in the following weeks, a second application may be required in early May for effective weed control.
Homeowners are able to purchase crabgrass preventers or crabgrass killers and apply them to their lawn if they wish. Common ingredient names of preemergence herbicides available for home lawns include benefin/trifluralin, pendimethalin, prodiamine and dithiopyr. Dithiopyr, commonly sold under the trade name Dimension, is the product of choice if herbicide application becomes delayed and crabgrass is already germinating at the time of application.
Corn gluten meal is a popular natural fertilizer that also has substances in it that are reported to inhibit crabgrass and other weed seed germination.
If areas of the lawn are reseeded or overseeded in early spring, no grass preventer herbicides should be applied since they will also kill the desired lawn seeds as they begin to germinate.
Once crabgrass germinates and emerges, although somewhat less effective than “preventers” there are a few postemergence products available to suppress or eliminate it from lawns. Common ingredient names of postemergence herbicides include MSMA (Monosodium methyl arsonate), DSMA (Disodium methyl arsonate), fenoxaprop, quinclora and dithiopyr (which is only effective on crabgrass seedlings).
When applying postemergence herbicides be sure to obtain thorough coverage and do not mow for two days before and after the herbicide application.
– Stan Smith, OSU Extension PA, Fairfield County