Q: I am looking to apply crabgrass preventer on my lawn, when is the best time to do that?
A: Crabgrass preventers are another name for pre-emergence herbicides that prevent crabgrass seeds from developing into mature plants. They do not keep the seed from germinating, but kill the young germinating plant. Crabgrass preventers are just that- preventers. With few exceptions they have no effect on existing crabgrass plants, so they must be applied before germination. Additionally, preventers do not last forever once applied to the soil. Microorganisms and natural processes break them down soon after they are applied. If some products are applied too early, they may have lost much of their strength by the time they are needed. Most crabgrass preventers are fairly effective after about sixty days, but there is considerable variation among products. For most of Kansas, crabgrass typically begins to germinate a little later than May 1 (the northwest tends to bloom later than most of the rest of the state). May 1 is a good target date for applying preventer because it gives active ingredients time to evenly disperse in the soil before crabgrass germination starts. It is often better to base timing on the bloom of ornamental plants, especially during a spring with non-typical weather, such as this year. The Eastern Redbuds planted in the town of Atwood is a good choice for this purpose. You can find Eastern Redbuds planted in the town of Atwood on the corner of 7th and Pearl St. When the Eastern Redbud is approaching full bloom, it is appropriate to apply crabgrass preventer. A follow application will be needed about 8 weeks later unless you are using Dimension or Barricade. These two products give season long control. They can be applied much earlier than May 1 and will have sufficient residual strength. Barricade can even be applied in the fall for crabgrass control the next season. Dimension can be applied as early as March 1. Though Dimension cannot be applied as early as Barricade, it is a herbicide of choice if it must be applied later than recommended. It is the exception to the rule that pre-emergent herbicides do not kill existing weeds. Dimension can kill crabgrass as long as it is young. (2-3 leaf stage) Products that require a follow-up application include pendimethalin (Scott Halts) and Team (Hi Yield Crabgrass control). Pendimethalin has better activity on broad leaves than any other crabgrass preventers. Normally a pre-emergence herbicide is not recommended unless the lawn has been mowed two-four times. Dimension can be applied to lawns established the previous fall, and is kind young tall fescue, perennial ryegrass and Kentucky bluegrass. Keep in mind that crabgrass preventers may be listed under their common name instead of the trade name. The common chemical name for Dimension is dithiopyr and for Barricade is Prodiamine. When using any pesticide When using any pesticide read the label and follow instructions carefully. Crabgrass preventers should be applied before fertilizer so that the grass isn’t encouraged to put on too much growth too early. However, it may be difficult to find products that contain pre-emergent with fertilizer. Those that don’t contain fertilizer are Pendimethalin (Scott Halts) Team (Benefin+Trifluralin) and Dimension products including Hi Yield Turf and Ornamental Weed and Grass Stopper, Bonide Crabgrass and Wood Preventer and Green Light Crabgrass Preventer. Brand names mention in this article are for informationa; purposes only, no endorsement is intended.
