Timing of Preemergence Herbicides – Turfgrass Science at Purdue University

Timing of Preemergence Herbicides

If a preemergence herbicide is justified on a turf area, the timing of application is important. In theory, applying too early will expose the herbicide to soil microbes and processes in the soil that may break it down, allowing crabgrass to germinate during the latter part of the summer. Conversely, applying too late may miss the early part of the germination window of crabgrass. Our research as well as research from other universities show preemergence herbicides break down very slowly in our cool spring soils. Applications made at the proper rate in late fall and early spring will provide adequate control throughout the summer. Therefore, when applying preemergence herbicides, it’s better to error on the side of being early than too late. We recommend applications no later than 15 Mar. to 1 Apr. in southern IN, 1 Apr. to 15 Apr. in central IN, and 10 Apr. to 25 Apr. in northern IN.

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