For Release March 19, 2002

Crabgrass Preventer Treatments, Is It Time?

by Chuck Otte, Geary County Extension Agent

With spring break this week, and some nice weather in the forecast, thereís a lot of homeowners getting the fever to get out in the yard and do something! One of the critical management practices that everyone wants to get done every spring is applying the crabgrass preventer. Unfortunately, to be very blunt, most people do not apply their crabgrass preventers properly.

Letís review the crabgrass life cycle. It is an annual grass. It sprouts after the last frost, produces a seed head and dies with the first frost. It needs warm soil to germinate. Here in northern Kansas it usually doesnít start germinating until very late April or early May. Seed can lay dormant and wait well into midsummer before it decides to germinate, and still have time to make seed before frost. Crabgrass does best where there is bare soil for it to germinate.

I always tell homeowners that crabgrass is a symptom, not a problem. It is a symptom that your lawn is not as lush and thick as it should be. And a common cause for thin lawns is mowing too short. Mow those fescue and bluegrass lawns as high as you can, but consider three inches the minimum.

Crabgrass preventers are just as their name implies. They prevent crabgrass by killing the young plant just as the seed germinates. Like all herbicides, crabgrass preventers have a limited active soil life. This can be anywhere from sixty days to six months, depending on the herbicide used. Many of the traditional products have fairly short soil active lives. To achieve good season long control you need to apply a follow up application eight to twelve weeks after the first application, as indicated on the label. There are a couple of newer products that have much longer soil active lives requiring only one treatment per season.

All of these products will do a very good job of controlling crabgrass IF they are applied in the proper manner, including a second application if so indicated. I did a quick survey this week of the local lawn and garden supply establishments selling lawn crabgrass preventers. The various products I found contained six different chemicals.

The new products are Dimension (dithiopyr) and Barricade (prodiamine). These products can be applied now with expectations of season long control from that one application. Dimension has an added attribute that it can be applied clear into early May. It has the ability to kill seedling crabgrass that is past the germination stage. The other products you may run into locally are Halts (pendimethalin), Team (trifluralin or treflan), Balan (benefin) and Tupersan. Tupersan is the only one that can be used on newly seeded grass for crabgrass control.

In general, the best time to apply these products is April 1 to April 15 OR when the redbud trees are in full bloom OR when the early morning soil temperature is 55 degrees. If there is not at least a quarter inch of rain within three days, water the product into the soil. Do not disturb the soil, such as power raking, after the application is applied. This breaks up the zone of control.

All of these products will do a good job of controlling crabgrass. Apply them at the right time, follow the label directions for a second application if needed, and then make your lawn as competitive as possible to reduce or eliminate the need for future crabgrass herbicide applications.


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