Crabgrass is a common lawn weed that can be prevented by using a properly timed pre-emergence herbicide application. Pre-emergence applications need to be made before crabgrass starts to grow, as these products work by containing a chemical that prevents weed seeds from germinating. Thus, applications made too late in the season will not provide control once the seed has germinated.

Germination of crabgrass occurs when soil temperatures at four inches stay above 55 degrees for three to four days in a row. Northern Iowa soils typically start warming up by mid-April, and once the soil has warmed, a pre-emergent is not an effective means for crabgrass control. Crabgrass continues to germinate over several weeks from spring into summer.

There are a few post-emergent products that homeowners can use on young plants. But for lawns with a history of large populations of crabgrass, pre-emergence applications provide better control. Always read and follow label directions.

Crabgrass is a summer annual weed, with a life cycle of growing from seed every year in the spring and then dying after hard frost in the fall. One crabgrass plant can produce thousands of seeds during the year. To help prevent crabgrass seeds from forming, keep lawns mowed to a proper height, especially mid-season, during the height of seed production. Unfortunately, crabgrass seeds can remain dormant in the soil for several years before germinating.

The best means for preventing crabgrass and other weeds is to maintain a thick, healthy lawn. A dense stand of turf can effectively shade the soil and help to reduce the number of weeds that are able to establish.

Did you know? Be safe when mowing steep slopes or ditches. Danger of mower rollovers are issues on steeper slopes or when making a tight turn too fast with rider mowers. Remember to reduce mower speed before making turns.  Consider replacing grass with ground cover that doesn’t require mowing on steeper areas.

Questions? Contact McCormick at yvonne@iastate.edu for information or advice.