Selecting a Crabgrass Preventer for Your Lawn
By Ron Honig
If you can find a day when the wind is not howling, now is the time to be applying crabgrass and broadleaf herbicides to cool and warm season lawns. Crabgrass preventers are simply preemergence turf herbicides that prevent crabgrass seeds from developing into mature plants. As the name suggests, preemerge herbicides must be applied before the grass germinates and begins to grow in order to get control. With a few exceptions, they have little to no effect on existing crabgrass plants. Early to mid-April is the recommended application period in Kansas.
Crabgrass, however is not the only common weed controlled by crabgrass preventers thus selecting the right herbicide can be a handy aid to controlling a number of other grasses and broadleaf weeds in your lawn such as dandelion and sandbur.
Following are four common active ingredients found in crabgrass preventers along with their common trade names: Prodiamine (Barricade), dithiopyr (Dimension), pendimethalin (Halts or Pendulum), and a combination of trifluralin and benefin (Team or Hi-Yield Crabgrass Control).
Of the four herbicides, prodiamine has the longest residual in the soil and provides the longest control of weeds listed in the product label. Because of this long residual, prodiamine is a good choice for applying in the late summer or fall for preemerge henbit (the spring weed with square stems and purple flowers) control. Henbit germinates in the fall or winter months and begins growth early in the spring.
Prodiamine also controls kochia which may germinate in late winter or early fall as well as pigweeds, shepherdspurse and prostrate spurge. Dandelions, however, are not on the label’s control list. Products vary, however a full-rate application of prodiamine can provide over six months of crabgrass control.
A fall prodiamine application, at the full application rate, should still provide weed control into the summer. A split application of a half-rate in early fall and another in the spring may extend weed control through July.
Dithiopyr, when applied at the full rate, also has a long residual of 3 to 4 months. Dithiopyr has the advantage of controlling many of the same weeds as prodiamine but with the addition of dandelion and sandbur.
Dithiopyr may also be applied in the fall like prodiamine, but if used in the fall, a second application in early summer will be needed to get season-long weed control from dithiopyr. If applied in the spring at the full application rate, expect weed control throughout much of the summer.
Pendimethalin controls a wide range of grass and broadleaf weeds including sandbur, henbit, kochia and a broadleaf weed called Redstem Filaree which we are seeing more and more of in this area. Dandelion is not on the label however, and henbit, filaree and kochia may emerge before pendimethalin is normally applied in mid-April.
Pendimethalin, unfortunately, has a shorter residual than either prodiamine or dithiopyr and will require a second application about six weeks of the first, even if applied in the spring. The product label will provide exact retreatment recommendations based on the concentration of the active ingredient.
The trifluralin and benefin combination in Team products control a smaller list of both grass and broadleaf weeds. Purdue University rates the level of crabgrass control from Team lower than that of the other products discussed previously. Team provides control of pigweed, prostrate knotweed and some foxtails along with crabgrass.
The four crabgrass herbicides mentioned do not control emerged weeds. These products are intended for preemerge control of weeds and are soil applied herbicides. The exception is that dithiopyr will control small, early-tillered crabgrass when applied post emerge.
After application, all of these herbicides need to be watered into the soil with either rain or approximately ½ inch of irrigation.
The addition of a 2,4-D- or dicamba-based herbicide either in dry or liquid form will help control emerged broadleaf weeds such as dandelion.
Most crabgrass preventers are marketed to homeowners with fertilizer in the product mix. The four herbicides discussed in this article can be ordered without fertilizer from garden stores or from online vendors. Follow label directions for the correct application rates and for the recommended timing of reapplications.
