Best Time for Crabgrass Herbicide Application Guide

By Scout Nelson

Graig Reicks, SDSU Extension Weed Ecology Field Specialist, along with Eric Jones, Nick Volesky, and Philip Rozeboom, highlight important practices for managing crabgrass in lawns. Preemergence herbicides play a key role in controlling this weed. The best time to apply these herbicides is usually during April, or earlier in warmer years. Crabgrass is a warm-season annual weed that begins to grow when soil temperatures reach about 60˚F.

It is important to correctly identify weeds before treatment. Crabgrass is often confused with quackgrass, but they are different. Quackgrass is a cool-season perennial weed that grows from both seeds and underground stems called rhizomes. It can survive cold weather and appears early in the season. One key feature of quackgrass is its clasping auricles, while crabgrass has a long, thin ligule. Correct identification helps in choosing the right control method.

Preemergence herbicides, often called crabgrass preventers, do not stop seeds from germinating. Instead, they kill young plants as they grow through treated soil. Common active ingredients include prodiamine, pendimethalin, and dithiopyr. These herbicides must be applied before crabgrass emerges to be effective. After emergence, only certain products like dithiopyr can provide limited control.

Proper application is necessary for good results. These herbicides need at least half an inch of rainfall to move into the soil. Applying them when soil temperatures are in the upper 40s or low 50s helps ensure timely activation. Care must also be taken when applying herbicides on new lawns, as they can damage young grass.

Different product options are available for users. Granular products are easy to apply and are commonly found in stores. However, some contain nitrogen fertilizer, which is not always recommended in early spring. Sprayable products are more cost-effective but require proper equipment and careful handling.

Even with proper use, some weeds may still appear. In such cases, postemergence herbicides can help manage remaining weeds. Since crabgrass often grows in patches, treating only affected areas can save time and money.

Overall, proper timing, correct weed identification, and careful product selection are key to effective crabgrass control and maintaining a healthy lawn.

Photo Credit: gettyimages-awakr10