Crabgrass (Digitaria sp.) is one of the most widespread grassy weeds found in Midwestern lawns. Crabgrass flourishes in full sunlight, high temperatures and can easily out compete common cool-season grasses, like our Kentucky Bluegrass. Crabgrass is a summer annual, which germinates in the spring, grows through the summer and dies with the first hard frost. They produce a tremendous amount of seeds in the mid to late summer when the days start to shorten. These seeds not only ensure next year’s crop of weeds, they can also remain dormant in the soil for many years before germinating. Generally, if you have crabgrass in your lawn, it will be there next year, also. Horticulturists say, “One year’s seed equals seven years weeding.” Gasp!!!
The easiest way to take care of crabrass is to take care of it during the spring season, rather than take care of it later on in the season. A well-timed application of a ‘pre-emergent’ is what you’ll need. Just as the name states, a pre-emergent prevents seeds from germination. Killing it before it emerges. Be aware that you can’t use this type of herbicide if you are planning to or have just recently seeded your lawn, as it will kill those seeds also. Timing is critical, as the herbicide does not last long and must coincide with the seed wanting to germinate.
Crabgrass seed will not germinate until the soil temperatures are 55F degrees at the one-inch level. The Illinois State Water Survey reports soil temperature at the four-inch depth at St. Charles reporting station was 47.5F degrees on April 16. The soil temperature at one-inch will be slightly higher. This suggests Northern Illinois is approaching the right conditions for application. Next week the weathermen say it will be warm and that will help the soil temperatures progress. North Americans can go to this site for application timing. Or the indicator plant that can be used for application timing is ‘forsythia is in bloom’. Late April (now) into early May will most likely be our target for 2019.
© The Naturarian