2,4-dimethylamine salt (2,4-D) is a synthetic auxin herbicide used extensively in turfgrass for selective broadleaf weed control. Previous research has shown that 2,4-D can dislodge from treated turf, notably in the presence of canopy moisture. Practitioners commonly apply 2,4-D in combination with various commercially available surfactants to increase efficacy. Field research was completed to evaluate the effect of surfactant inclusion and sample collection time within a day on dislodgeable 2,4-D residue from perennial ryegrass. Research was initiated May 24, 2016 in Raleigh, NC and repeated in time to quantify dislodgeable 2,4-D following application (2.1 kg ae ha–1) either alone or with a nonionic surfactant (0.5% vol/vol). Sample collection occurred 1, 2, 3, 6, 12 or 24 d after treatment (DAT) at AM [7:00 AM Eastern Standard Time (EST)] and PM (2:00 PM EST) sample timings within a day. 2,4-D applied with surfactant (0.4% to 25.4% of applied) reduced dislodgeable foliar residue compared to 2,4-D applied alone (0.5% to 31.2%) from 1 through 6 DAT, whereas dislodgeable 2,4-D was not detected at 12 and 24 DAT. Regardless of surfactant inclusion or absence, samples collected in the AM resulted in a 5- to 10-fold increase in dislodgeable 2,4-D compared to samples collected in the PM from 1 through 6 DAT, suggesting that 2,4-D dislodgeability may be influenced by conditions favoring canopy moisture development. This research will improve turfgrass management practices and research designed to minimize human 2,4-D exposure.

Herbicides commonly used to control Cyperus spp. are not completely effective against Kyllinga spp. Field trials were conducted on North Carolina golf courses to evaluate green and false-green kyllinga control at fairway and rough golf course mowing heights. Treatments included single and sequential applications of bentazon (1.12 kg ai/ha), halosulfuron (0.07 kg/ha), MSMA (2.24 kg/ ha), and trifloxysulfuron (0.03 kg/ha); imazaquin (0.56 kg/ha) with and without MSMA; and two rates of sulfentrazone (0.42 and 0.56 kg/ha). Green or false-green kyllinga control was equivalent at fairway and rough mowing heights. Halosulfuron applied sequentially, imazaquin with and without MSMA, and trifloxysulfuron applied singly or sequentially, controlled green and false-green kyllinga 89 to 99% 10 wk after initial treatment (WAIT). However, Kyllinga spp. control decreased over the course of the study regardless of herbicide treatment. By one year after treatment (YAIT), bentazon or MSMA alone controlled green or false-green kyllinga 50% or less. No difference was observed in green or false-green kyllinga control between imazaquin vs. imazaquin plus MSMA, sulfentrazone 0.42 vs. 0.56 kg/ha, or trifloxysulfuron one vs. two applications at any rating date. Green kyllinga was seemingly more difficult to control than false-green kyllinga. Sequential applications of bentazon and MSMA, single applications of halosulfuron, sulfentrazone applied at 0.42 and 0.56 kg/ha, and single and sequential applications of trifloxysulfuron controlled false-green kyllinga at least 10% greater than green kyllinga at 1 YAIT. Further research is needed to assess the potential variation among Cyperus and Kyllinga spp. response to herbicides.

Knowledge of the influence of environmental factors on weed populations is important in developing sustainable turfgrass management practices. Studies were conducted to evaluate the relationship of green and false-green kyllinga population densities with elevation and edaphic factors in turfgrass systems. Studies were conducted on five different golf courses in North Carolina, three affected by green kyllinga, and two affected by false-green kyllinga. According to Spearman correlation coefficients, both green and false-green kyllinga were correlated with increasing soil volumetric water content, whereas correlation of other edaphic variables varied among sites and species. Stepwise logistic regression confirmed the correlation of volumetric water with green kyllinga presence, but model components varied among sites for false-green kyllinga. Increasing green kyllinga populations correlated with increasing soil sodium; however, sodium did not reach a level believed to be detrimental to turfgrass growth. No other variables correlated with green or false-green kyllinga across all sites. We hypothesized that the lack of significant correlations was due to the overall influence of relative elevation on edaphic variables. According to principal components analysis (PCA), relative elevation had a profound impact on the measured edaphic variables at all sites. However, results of PCA at one site differed sharply from other sites. Results from that site demonstrate the potentially strong effects of management practices to alter edaphic trends normally observed with topography.

Annual bluegrass is commonly controlled by acetolactate synthase (ALS)-inhibiting herbicides in managed turfgrass. An annual bluegrass population with suspected resistance to ALS-inhibiting herbicides was collected from Grand National Golf Course in Opelika, AL (GN population). Subsequent testing confirmed resistance of the GN population to foramsulfuron, trifloxysulfuron, bispyribac-sodium (bispyribac), and imazaquin when compared to a susceptible population collected locally at Auburn University (AU population). Sequencing of the ALS gene revealed a point mutation resulting in an amino acid substitution at Trp574. Cloning of the ALS gene surrounding the Trp574 region yielded two distinct ALS gene sequences: one producing Trp574 and one producing Leu574. Trp574 to Leu has been previously correlated with resistance to ALS-inhibiting herbicides. Both AU and GN gene sequences contained other similar silent and missense mutations. This research confirms resistance of annual bluegrass to ALS-inhibiting herbicides with Trp574 to Leu amino acid substitution being the most likely mode of resistance based on past literature.