Crabgrass (Digitaria spp.) is a common weed of warm- and cool-season turfgrasses. A survey of the southern United States conducted by Webster (2000) ranked crabgrass as the most common turfgrass weed in 10 of 12 southern states. Compared with desirable turfgrass species such as bermudagrass (Cynodon spp.) or tall fescue (Lolium arundinaceum Schreb.), the light green color and coarse texture of crabgrass foliage can reduce overall turf quality (Hall et al., 1994). PRE herbicides such as dithiopyr, indaziflam, oxadiazon, prodiamine, and pendimethalin are labeled for selective control of smooth crabgrass (Digitaria ischaemum Schreb.) and large crabgrass [Digitaria sanguinalis (L.) Scop.] in turf (Anonymous, 2012a, 2012b, 2012c, 2007, 2009).
Previous research has reported reductions in crabgrass cover by increasing turf mowing height. Specifically, Dernoeden et al. (1993) reported ≈3% smooth crabgrass cover in non-treated tall fescue mowed at 8.8 cm compared with 40% and 80% smooth crabgrass cover in plots mowed at 5.5 and 3.2 cm, respectively, at the conclusion of a 3-year study. Reductions in smooth crabgrass cover with increased mowing height have been observed in other cool-season turfgrass species, including kentucky bluegrass (Poa pratensis L.), tall fescue, perennial ryegrass (Lolium perenne L.), and several fine fescue species (Festuca spp.) (Debels et al., 2012; Dernoeden et al., 1998; Dunn et al., 1981; Jagschitz and Ebdon, 1985; Voigt et al., 2001). To date, minimal information has been published regarding effects of mowing height on crabgrass cover in warm-season turfgrass species such as common bermudagrass (Cynodon dactylon L.) (Callahan, 1978; Hoyle et al., 2014).
Integrated pest management has been defined as the thoughtful combination of multiple approaches such as synthetic chemical applications and cultural practices to control pests (Busey, 2003). Although the efficacy of PRE herbicides for crabgrass control and effects of mowing height on crabgrass incidence have been studied, research exploring the integration of these two practices is limited. Dernoeden et al. (1993) monitored smooth crabgrass cover after applications of dithiopyr and pendimethalin to tall fescue turf maintained at 8.8, 5.5, and 3.2 cm. Herbicide rates were reduced by 50% at the end of the 3-year study and plots mowed at 5.5 and 8.8 cm did not require a herbicide in the final year of the experiment. Smooth crabgrass cover in dithiopyr- or pendimethalin-treated plots was similar (3% or less) during the first 2 years of the study, regardless of mowing height. However, in the third year, smooth crabgrass cover was greater in tall fescue turf mowed at 3.2 and 5.5 cm than 8.8 cm after pendimethalin or dithiopyr application. The researchers concluded that annual dithiopyr or pendimethalin applications at labeled rates would be required when mowing tall fescue at 3.2 and 5.5 cm. However, reduced rates and less frequent applications of these herbicides could provide acceptable turf quality when mowing height was increased to 8.8 cm.
Changes in common bermudagrass mowing height may affect the efficacy of PRE herbicides labeled for crabgrass control. However, minimal data have been published regarding integrated programs for managing crabgrass infestations using PRE herbicides in combination with mowing height adjustment. Therefore, the objective of this research was to determine the effect of mowing height on the efficacy of several PRE herbicides labeled for crabgrass control in common bermudagrass turf.
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