Does it matter when you put down crabgrass preventer in the spring? You bet it does!
Crabgrass preventers are another name for pre-emergence herbicides that prevent crabgrass seeds from developing into mature plants. They don't actually keep the seed from germinating; rather, the germinating plant takes up some of the herbicide and is killed.
With few exceptions, however, they have no effect on existing crabgrass plants. Most crabgrass preventers are ineffective after about 60 days. And, since, crabgrass typically begins to germinate around May 1 or a little later, you should apply preventer around April 15.
This gives the active ingredients some time to evenly disperse in the soil before crabgrass germination starts. Another good "rule-of-thumb" is when the Eastern redbud trees are approaching full-bloom, apply your crabgrass preventer.
If you are in a situation where you must seed this spring, you have two options for crabgrass control.
Tupersan is a product that can be used at the time of seeding. It is somewhat less effective than other pre-emergence herbicides but it is safe to the newly seeded grass.
Dacthal is more effective for crabgrass control but should not be used until the new seedlings are one inch tall. Both Tupersan and Dacthal give short-term control so an additional application will be necessary about six weeks after the first.
If your lawn is established, Barricade and Dimension are two products that can be used earlier in the year and will give season-long control of crabgrass.
Dimension can be applied as early as March. Dimension is also unique in that it can even be applied after the crabgrass has germinated, as long as the plants are still small. Consequently, Dimension can often be applied well into the month of May with very good results. Barricade can even be applied in the fall for crabgrass control next season.
Theoretically, mowing low in the spring facilitates warming of the soil which promotes growth; raising the height during the summer enhances stress resistance, and mowing lower in the fall is supposed to promote tillering which increases lawn density.
However, continuing to mow short through the spring may allow crabgrass to get established. A dense lawn mowed on the high side accomplishes a great deal of crabgrass control.
-- The Garden Calendar is sponsored by K-State Research and Extension-Douglas County office and written this week by Pat Risley, Master Gardener. For more information call the Master Gardener Hotline, 843-7058, Monday-Friday, between the hours of 1 p.m. and 4 p.m.