Is this year (2019) the year for explosive crabgrass? Were the conditions for heavy seeding?

Asked August 21, 2019, 11:23 AM EDT

We live on 4 acres in Oakland county, and always bragged that our grass never needed watering or fertilizer and always looked good and green and lush, although always had some lawn weeds, but looked great after it was mowed. This year in a matter of weeks it seemed everything turned to crabgrass. The lawn is 35 years old but Always looked good. Now it's lighter green, and thick with crabgrass. Is there a way to reverse all this mess?.

Oakland County Michigan

1 Response

Hello,

It is too late this year to use the postemergence controls. Crabgrass is an annual and so all of it will die when weather turns cool.

This seems to be a high year for crabgrass in my neighborhood, too. Only the thick lawns who had the pre-emergent with fertilizer followed by fertilizer with weed killer seem to be exempt.

One thing this spring was an unusual amount of rain distributed fairly evenly ( not just in a couple heavy downpours that mostly run off). This leaches fertilizer and chemicals from the soil more quickly, reducing their longevity. This was followed by some hot dry weather that started to turn grass dormant, and allowed crabgrass to get a start. So, crabgrass has had a easier time of establishing itself this year.

This information is from MSU’s Turf Weeds website:

“Elevated mowing heights and judicious nitrogen fertilization can be extremely effective at reducing competition from crabgrass. Research studies have shown up to 95% reduction in crabgrass when mowing height is increased from 1.5 to 3.0 inches. Thin turf in the spring or drought conditions often lead to major infestations of crabgrass.

Preemergence Control- Smooth crabgrass is the most common summer annual grassy weed in Michigan. Preemergence herbicides are the most common and least expensive chemical controls for crabgrass. Properly timed applications of preemergence herbicides including benefin+trifluralin, pendimethalin, dithiopyr and prodiamine will all provide excellent control of large crabgrass.

Postemergence Control- Several postemergence herbicides are labeled and effective for removing established plants of large crabgrass. As a rule, younger plants are easier to control. MSMA is the most common postemergence herbicide used for annual grassy weeds. The effectiveness of MSMA will be improved in warmer conditions. MSMA is available as a stand-alone or in combination with phenoxy acid herbicides. Fenoxyprop-ethyl is very effective on crabgrass through the 3-4 tiller stage. Quinclorac has faster activity than MSMA or fenoxyprop and is effective on very mature crabgrass. Quinclorac is available as a stand-alone or in combination with 2,4-D, dicamba and sulfentrazone. Dithiopyr has true PRE and POST activity. Properly timed applications of dithiopyr can eliminate 1-3 leaf crabgrass and establish a preemergence barrier that will last for the remainder of the season.

Disclaimer:Always read, understand, and follow the label directions. Mention or exclusion of specific products does not represent an endorsement or condemnation of any product by Michigan State University.”


If your grass has been thinned as a result of being shaded out by the crabgrass you will need to encourage it by keeping it watered during dry times ( about 1 inch a week divided over 3-4 waterings and counting rainfall in the 1 inch), mow no shorter than 3 inches to encourage longer roots, and apply a fall fertilizer to get it ready for winter. Mulching the clippings returns some nutrients to the soil, reducing the need for fertilizer. Thin spots can be over seeded when weather turns cool this month, or in spring. Next spring when forsythia are in bloom is the time to apply a pre-emergent to prevent crabgrass. Perhaps following a traditional care plan like this will return your grass to its thick status, which will shade out most crabgrass germination.

If you need details on these techniques, here are lawn care websites

https://www.canr.msu.edu/home_lawns/

http://www.msuturfweeds.net

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