provides pre-emergence and early post-emergence crabgrass control. Dimension may stunt growth of crabgrass when applied after tillering but generally will not provide acceptable control. Therefore, you should apply this compound prior to tillering. An advantage of Dimension is that can provide three or more months of residual crabgrass control. Crabgrass is one of the few weeds Dimension will control post-emergence. You could control crabgrass for most of the growing season with one Dimension application appropriately timed after emergence.
is a root inhibitor, and works by affecting cell division in grass roots. You should only apply it to established turf, because established turf has a well-developed root system. You can apply this herbicide to a wide range of cool and warm-season turfgrass species. Check the label for sensitive cultivars, especially bentgrass and fine fescue. Many ornamentals tolerate Dimension, and you can use this compound for weed control in ornamental beds as a directed spray.Drive (quinclorac)
is a unique herbicide. When looking at its weed control spectrum and the injury symptoms it causes, it appears to be a hybrid between a grass herbicide and a broadleaf herbicide. It controls crabgrass both post-emergence and pre-emergence, with a month or more residual control after treatment. Drive will not control all broadleaves, so combinations with 2,4-D and other broadleaf herbicides will increase the number of broadleaf weeds controlled. Drive can be less effective when applied during crabgrass tillering, so pretillering applications would be the preferred time to apply the chemical. Adding a methylated seed oil as an adjuvant improves leaf uptake and, thus, weed control.
Drive inhibits cellulose biosynthesis in plants, and may also have other sites of action. Drive can injure susceptible broadleaf plants through leaf or root uptake. Do not use lawn clippings to mulch vegetables or other broadleaf crops because Drive can damage crops like tomatoes. It can cause injury in certain broadleaf ornamentals, so avoid spray drift when treating lawns near flower and shrub beds. Depending upon the turf species, there is flexibility in regards to seeding of turfgrass after a Drive application, and applications can be made to relatively young turf. Drive cannot be applied to certain turfgrass species, such as St. Augustine and centipedegrass.
The organic arsenicals MSMA and DSMA
(various trade names) also control emerged crabgrass in established turfgrass. Generally, multiple applications are required, especially for well-tillered crabgrass. The organic arsenicals can cause yellowing or burning of turf, such as in tall fescue. This injury is temporary and turfgrass will outgrow the damage in a week or two. An advantage to using organic arsenicals is control of sedge species like yellow nutsedge. The organic arsenicals are also sold commercially in combination with broadleaf herbicides like 2,4-D. This is one-stop shopping, if you will, because these mixtures will suppress or control a wide range of broadleaf, grass and sedge weeds. A disadvantage to these combinations is that a given site may only have broadleaf weeds, so the MSMA or DSMA is not required, while other sites may have only crabgrass and, thus, not require the 2,4-D component. MSMA and DMSA do not provide residual crabgrass control, so you must either repeat applications for later-germinating plants or apply a pre-emergence herbicide. Follow label directions in regard to addition of a nonionic surfactant.Acclaim Extra (fenoxaprop) is a post-emergence herbicide with little-to-no soil residual effects. It is primarily used in cool-season turfgrass, and can be used to suppress bermudagrass that has invaded turfgrasses like Kentucky bluegrass and tall fescue. Acclaim Extra will not control any broadleaf weed or sedge species. Post-emergence broadleaf herbicides like 2,4-D, dicamba or triclopyr can antagonize crabgrass control with Acclaim Extra if you do tank mixes. You can avoid this by applying Acclaim Extra first, then waiting a week or two before applying the broadleaf herbicide. Acclaim will control pre-tillered and tillered crabgrass, but higher application rates are required for larger crabgrass plants. You can combine Acclaim Extra with pre-emergence crabgrass herbicides to obtain residual control.
inhibits fatty acid synthesis in sensitive weed species. The old formulation of fenoxaprop, Acclaim 1EC, contained two forms of the herbicide: one that controls weeds and another form that is essentially inactive. The manufacturer was able to synthesize only the active formulation of the herbicide, resulting in lower rates of application for the active ingredient. Acclaim Extra only contains the active form of fenoxaprop. Acclaim Extra can cause temporary yellowing in some grasses like Kentucky bluegrass, but the turf will quickly outgrow any adverse effects. Broadleaf ornamentals are tolerant of Acclaim Extra, so you could also use this chemical for crabgrass control in landscape beds.MIX IT UP
Why did I mention the mechanism of action for these herbicides? One reason is the occurrence of weed resistance. Some parts of the country have crabgrass biotypes that are resistant to certain post-emergence crabgrass herbicides. To avoid development of herbicide resistance, rotate herbicides with different modes of action. Do not rely on the same herbicide year after year. It would be a good idea to rotate herbicides every three or four years. Because Dimension, Drive, the organic arsenicals and Acclaim Extra all have a different mode of action, any rotation among these chemicals will reduce the potential for crabgrass resistance.
Lawn care companies have a range of options for crabgrass control, including strictly pre-emergence herbicides, strictly post-emergence herbicides or a program utilizing both options. You should base your choice of a post-emergence crabgrass herbicide on the turfgrass species you will treat, the crabgrass size and the presence of other weed species. Combinations with pre-emergence herbicides will control both emerged crabgrass and provide residual control.
Jeffrey Derr is a professor of weed science at Virginia Polytechnic Institute and State University (Blacksburg, Va.).