Prevent crabgrass emergence

Spring officially arrives March 20 at 12:15 p.m., and along with basketball’s “March Madness” comes the drive in many of us to get outside and do something in the lawn.

Those who should get busy first are probably those who battled crabgrass last year. Homeowners who had a crabgrass problem should consider some type of crabgrass preventer application before very long. I like to tell people that it’s a good task to complete before school spring break is over.

Crabgrass is what we call a summer annual weed. In other words, seeds sprout in the spring, it grows and produces seed through the year, and completely dies before winter. So, crabgrass is not a perennial plant like our lawn grass is.

Crabgrass has a broader leaf than most normal lawn grasses, and a seed head with 3-5 spikes clustered at the top of stems.

Good cultural practices like mowing high and encouraging dense turf are the most effective crabgrass controls, but herbicides may be necessary in some cases.

Crabgrass herbicides available to homeowners are primarily “preventer” products, meaning that they need to be in place before crabgrass emerges. The way they work is that as soon as new seeds sprout, they come in contact with the product, die and fail to emerge. Many of these products are combined with fertilizer, however early spring fertilization of turf should be minimized. Look for products with mostly “slow-release” forms of nitrogen.

Pre-emergence herbicides must be applied early in the spring to be effective (best from March 1 to about mid-April in northern Indiana) — at least a week or two prior to germination of crabgrass. If you make earlier applications, they should also be effective. Data shows the average historical crabgrass germination date to be about April 29 in Fort Wayne. Of course, this will vary based on your location. And, the weather may vary that date from year to year. Crabgrass germinates when soil temperatures are approximately 60 degrees for 3-5 days at the one-quarter inch level.

A forecasting model developed by Michigan State University can help Midwest homeowners and professionals with the timing of their crabgrass preventer product applications and offer average crabgrass germination dates based on heat unit accumulations. You can stay up-to-date with the forecasts by visiting the model at gddtracker.net.

Do not use pre-emergence crabgrass preventers on newly seeded lawns, as they may inhibit desirable lawn species from growth and establishment.

Post-emergence herbicide products are available and are most effective on small crabgrass plants, but the products are very difficult to use effectively by most homeowners. Post-emergence treatment is probably best left to professionals. Do not attempt to control crabgrass with herbicides after mid-July because crabgrass plants are usually too large to control effectively.

When using any herbicide, always read and follow all label instructions.

For more information, access Purdue Extension’s free publication, “Control of Crabgrass in Home Lawns,” number AY-10-W, at The Education Store mdc.itap.purdue.edu (search for “crabgrass”).

John Woodmansee is an extension educator in Whitley and Noble counties.

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