Before and after

In many parts of the country, control of crabgrass and other annual grassy weeds was more difficult this past year than in typical years. Parts of the Midwest experienced warmer than normal temperatures in the spring which resulted in crabgrass germinating about three weeks earlier than normal.

Thus, anywhere pre-emergent herbicides had not been applied about three weeks earlier than normal saw a lot of crabgrass this year.

Pre-emergent herbicides continue to be our main line of defense against annual grassy weeds.

However, a recent trend in the industry is toward the introduction of products that offer effective control of crabgrass both pre- and postemergence. Some of these are new chemistries and some of them are combinations of existing products.

A review of the various pre and postemergent crabgrass controls, and their advantages and disadvantages follows.

Preemergent herbicides
There are several pre-emergent herbicides labeled for the control of annual grasses, such as crabgrass and goosegrass, in both cool and warm season turfgrass (Table 1). Note that not all of these products are registered for use in all species of turfgrass. For example, atrazine, metalochlor, napropamide, oryzalin, pronamide and simazine are registered only for use on warm season turfgrass. You should consult the label to make sure that the product is safe to the turf species that you are managing.

Benefin and benefin-containing products are older industry standards and provide effective and economic control of crabgrass. DCPA went off the market in the late 1990s but is once again available. Benefin and DCPA have the potential to breakdown more rapidly in thatchy turfgrass. Herbicides, such as bensulide, pendimethalin, prodiamine and dithiopyr, can be effective for up to four months. Many of these products have been around in the industry for a very long time.

A lot of recent product introductions have been not new chemistries, but rather generic versions of older herbicides. In fact, the only recent preemergent herbicide introduction for use in turfgrass is dimethinamid-p (Tower herbicide).

Tower is labeled for preemergence control of goosegrass and certain other grassy weeds and is safe for use on short cut creeping bentgrass. The other goosegrass product on the list is oxadiazon. There are also products that combine oxadiazon with either benefin, bensulide, or prodiamine.

Proper application of the right pre-emergent herbicide can result in 95 percent control of crabgrass and other labeled annual weeds for the duration of the season in northern climates. One concern with preemergent herbicide use is timing of application. The product must be applied ideally two weeks prior to germination.

Postemergent Herbicides
Fewer products are available for post-emergent control of crabgrass and goosegrass.
The organic arsenicals, DSMA and MSMA, do not appear in the Table 1 because their uses in residential turf were phased out after 2009 and all other uses have been severely restricted and are to be phased out by 2012.

Fenoxaprop has been on the market since the mid 1990s and gives good control of young crabgrass. However, control with tillering crabgrass is not as consistent. 

Quinclorac can give better control of young crabgrass and also late-tillering crabgrass (>6 tillers).

The author is an associate professor of turfgrass science at Ohio State University.