Preemergence herbicides (02-07-05)

It is time to purchase your preemergence herbicide and get ready to apply within the next couple of weeks. Keys for success with preemergence herbicides are: TIMING, RATE, UNIFORM COVERAGE, and ACTIVATION.

Preemergence herbicides must be applied prior to weed seed germination to be effective. Crabgrass seed germinate when soil temperatures reach around 58 º, so if crabgrass is a target weed you need to consider getting your preemergence herbicides on to your lawn very soon.

The herbicide label will provide a list of the weed species the active ingredient will control and at what rate. If there are several weed species that you are targeting use a rate that controls the most difficult weed. Caution should also be taken to stay within rates labeled for your specific turf species.

Preemergence herbicides create a thin weed control barrier on the soil surface. This barrier must provide complete coverage at a uniform rate to prevent any voids that would allow weed escapes. Liquid or granular application equipment should be accurately calibrated prior to making an application to ensure proper rates and coverage.

Finally, once the herbicide is applied it must be activated. This usually requires approximately one-half inch of rainfall or irrigation shortly after application to move the herbicide down through the leaf canopy to form the thin herbicide barrier at the soil surface. Always READ THE LABEL carefully before applying any pesticide.

Published February 7, 2005

Dr. Wayne Wells is an Extension Professor and Turfgrass Specialist. His mailing address is Department of Plant and Soil Sciences, Mail Stop 9555, Mississippi State, MS 39762. wwells@ext.msstate.edu