GOSHEN, Ind. — I often joke that crabgrass is the state weed of Indiana. This year, the joke isn’t funny. I cannot recall a year when crabgrass has been so prevalent. Why did this happen?
We have to look back to our spring weather and the weed’s growth habits to explain this. Crabgrass is a summer annual weed that begins germinating when soil temperatures are approximately 60º F for 3-5 days. For most of us in the Michiana area, the temperatures reached that point around April 20-30 in 2018.
The other requirement for crabgrass to germinate is moisture, and we had a lot of rain in May and early June. In fact, it seems that it would never stop raining at times. Our bluegrass lawns loved the rain, and grew steadily in May. But hidden in that dense bluegrass were some crabgrass plants waiting for their chance to thrive.
Towards the end of June, the rains stopped. When bluegrass doesn’t get enough moisture, it protects itself by going dormant. By mid-July, most non-irrigated lawns were brown and dormant. The crabgrass, and several other species of grass like fescue and foxtail, no longer had to compete with the bluegrass for water and space, and took off like a wildfire in California. Against the brown backdrop of the dormant bluegrass, the crabgrass has stood out like a sore thumb.
Crabgrass ﬂowers and sets seed in July and August, then dies with the first frost of fall. Most of our crabgrass has been dropping seeds since late July, meaning that it is too late to effectively control crabgrass with herbicides. Even so, the herbicides available to us for killing emerged crabgrass are not very effective unless the plants are small. The bottom line is, it is too late to try to control crabgrass with herbicides.
Do not attempt to control crabgrass with herbicides after mid- July because crabgrass plants are too large to control effectively. It is better to simply tolerate the crabgrass until it dies with the ﬁrst frost.
What can you do now? By maintaining a dense lawn, you can limit the amount of crabgrass. Proper fertility, mowing, and irrigation is essential for crabgrass control; consider herbicidal control only if necessary. Consider fertilizing your lawn in early September with a quality slow release fertilizer. If dry weather visits us again, consider watering the lawn. Mow no lower than 3 inches in height. Mowing lower gives the crabgrass a competitive edge, even though it may seem like you are cutting off more of the crabgrass seed heads.
You might want to consider using a crabgrass preventer next spring. The preventer must be applied before the crabgrass germinates. Generally, in our region, the application can be put down around the week of April 1 without any concern of the product wearing off too early in the season.
Want more information about crabgrass and lawn care? Check out Purdue turf publications at https://turf.purdue.edu/homeowner.html
If you have other plant questions, please feel free to call our office at 533-0554. We have Master Gardeners working a part time Answer Line most days of the week, and they would love to help you.
— Jeff Burbrink, Extension Educator, Purdue Extension Elkhart County
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