Want To Control Crabgrass? Time To Apply A Preemergent!

Our mild winter is resulting in an early spring; plants are in flower, garden centers are stocking their shelves and weed seeds are starting to germinate. Large crabgrass (Digitaria sanguinalis ) is a summer annual grassy weed. Summer annuals germinate in the spring, grow through the summer and die with the first hard frost. These plants produce a tremendous amount of seed in the mid- to late summer. These seeds ensure next year’s crop of weeds but can also remain dormant in the soil for several years before germinating.

Crabgrass established in lawn.

Crabgrass established in lawn.

Crabgrass thrives under close mowing conditions and in open areas with thin turf. Cultural activities that increase the vigor of turfgrass also decrease the potential of crabgrass invasion. These include using the proper mowing height for your specific turf, selecting the best turf species for your area, applying fertilizer at the correct time of year, and proper irrigation.

If your cultural practices are missing the mark, then a preemergent application may be needed. To be effective, preemergent herbicides must be in place before germination occurs. This will allow the herbicide to form a barrier before the crabgrass seedlings emerge. Preemergent herbicides work by inhibiting the growth of young seedlings. These products do not eliminate established plants. Crabgrass will start to germinate when soil temperatures reach 55oF at a depth of 1 to 2 inches for five consecutive days.

Crabgrass seedlings

Crabgrass seedlings.

Preemergent treatments are preferred because they are generally more effective for crabgrass control and less injurious to the turfgrass than postemergent treatments. Preemergent herbicides are effective only if they are applied uniformly and are watered into the soil by rainfall or irrigation before the crabgrass or other target weed emerges. Refer to the product label for information on the amount of water required. Table 1 is a list of common active ingredients that provide suitable preemergent crabgrass control when applied before germination.

Table 1. Examples of preemergent crabgrass herbicides.

Active Ingredient Brand Names
Bensulide Bensumec, Pre-San
Benefin Balan
Dithiopyr Dimension
Pendimethalin Pendulum
Prodiamine Barricade
Oryzalin Surflan
Oxadiazon Ronstar

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