Cleaning up Emerged Crabgrass

Postemergent Crabgrass Control Options

By Matthew Bertucci Ph.D., Research Scientist, University of Arkansas School of Crop, Soil and Environmental Science

All turfgrass professionals recognize the unwelcome sight of crabgrass emerging through a managed turf site. Crabgrass is undesirable due to its coarse leaf texture, pale green color, and reduced traffic tolerance. It is a summer annual weed that germinates in the spring (usually when soil temperatures reach 53 to 58°F), grows vegetatively over the summer and sets seed in the late summer and fall. Crabgrass is most vulnerable and easiest to control as seeds germinate; thus, preemergent herbicide applications in late February or early March are the most common and effective strategy for control of crabgrass. However, sometimes the pesky crabgrass emerges despite preemergent herbicide applications!

There are several reasons why a preemergent herbicide application could fail to control crabgrass. Oftentimes, a failure in weed control is simply a result of herbicides being improperly applied. A careful inspection of weed incidence and distribution across the treated site might reveal the specific problem. Is the crabgrass emerging in a strip as wide as the sprayer’s swath? That’s good evidence that an applicator missed a pass. Is a narrow band repeating across the property? Perhaps a nozzle was clogged or a narrow skip occurred between passes. In the worst cases, crabgrass may have emerged across the entire site. That could be due to a mistimed application of preemergence herbicides (after crabgrass emergence), lack of activation of the herbicide from irrigation or timely rainfall, or a mistake when measuring and mixing products. One final scenario is that the preemergent herbicide performed as expected, but the residual activity has diminished with time, allowing a late-season flush of crabgrass. It is important to understand why a preemergent herbicide application failed so the same mistake can be avoided in the future.

Regardless of how crabgrass managed to invade a turf site, the good news is that postemergent control of crabgrass is possible. As a general rule, smaller crabgrass plants are easier to control than larger plants. Larger crabgrass plants that have begun to tiller may require sequential postemergent applications to achieve complete control. Specific herbicide recommendations and rates are dependent on the site restrictions and turfgrass species. A list of chemicals and products that offer postemergent crabgrass control is listed below:

• Asulam (Asulox ® or Asulam) is labeled for sod farms only, specifically for use in St. Augustinegrass and ‘Tifway’ 419 bermudagrass only. No surfactant is required for application. Do not apply to stressed or freshly mowed turf.

• Celsius ® (thiencarbazone, + iodosulfuron + dicamba) controls grasses and broadleaf weeds in warm-season turf types in commercial and residential sites. Celsius only controls young crabgrass and may require sequential applications.

• Dithiopyr (Dimension ® ) is labeled for preemergent control of crabgrass in established warm and cool season turf. However, it can be applied for postemergence control of young crabgrass seedlings and offer residual control following application.

• Mesotrione (Lucto™, Slipstream™, Tenacity ® ) offers contact and residual weed control in turf. Mesotrione can cause severe injury to actively growing bermudagrass, zoysiagrass, creeping bentgrass, and other turfgrass species. Postemergent control of crabgrass will require sequential applications at two-week intervals.

• MSMA (Target ® or MSMA) can offer postemergence control of crabgrass but is only labeled for sod production and use on golf courses. Be sure to check the label for instructions.

• Pinoxaden (Manuscript ® ) is a newly registered herbicide labeled for use in bermudagrass and zoysiagrass, and also for St. Augustinegrass in sod production only. The label requires that the product must be applied with a methylated seed oil surfactant.

• Quinclorac* (Drive ® , Drive ® XLR8, and others) — is a staple postemergent crabgrass product labeled for use in many environments. It is labeled for use in a wide range of turfgrass species; however, St. Augustinegrass, centipedegrass, and bahiagrass are sensitive to quinclorac and will likely be injured by applications.

*Note that many popular products contain quinclorac for crabgrass control plus other active ingredients for control of additional weed species. Some examples include Onetime ® (quinclorac + MCPP + dicamba); Q4 ® (quinclorac + sulfentrazone + 2,4-D + dicamba); SquareOne ® (carfentrazone + quinclorac); Solitare ® (sulfentrazone + quinclorac). These products all offer postemergence crabgrass control, but quinclorac is the only active ingredient within those formulations that works on crabgrass.

• Topramezone (Pylex™) is a similar mode of action to mesotrione and offers similar control of crabgrass, requiring sequential applications at three-week intervals. A major difference is that topramezone is labeled for use in creeping bentgrass, unlike mesotrione.

• Sethoxydim (Segment ® ) offers broad spectrum control of annual and perennial grass weeds. Sethoxydim is only for

use in centipedegrass or fine fescue. It will harm or kill other turfgrass species!

Some key points to remember:

Don’t make the same mistake twice. If a mistake was made during applications of preemergent herbicides, correct that mistake to avoid the necessity of postemergent applications in subsequent seasons.

Hit them when they’re small. Postemergent herbicides will have greater success on young, actively growing plants than mature, fully-tillered crabgrass.

Be careful not to harm your turf. Applying postemergence herbicides when temperatures are above 85°F may cause unacceptable turf injury. If possible, consider delaying postemergence treatments on particularly hot days.

The label is the LAW. Always read and follow label instructions when applying herbicides. It outlines how to safely, effectively, and legally apply products.

Use of specific trade names is for convenience to readers and does not represent any specific endorsement by authors. Feel free to contact Dr. Matthew Bertucci for concerns or questions at bertucci@uark.edu or via twitter @BertucciUARK. Additional information can be found in MP521 — Turfgrass Weed Control and MP44 — Recommended Chemicals for Weed and Brush Control.