Annual bluegrass (Poa annua L.) is a problematic weed on creeping bentgrass (Agrostis stolonifera L.) putting greens. Annual bluegrass produces extensive seedheads in spring, and plant growth regulators (PGRs) are frequently used to suppress seedhead formation. This study investigated the effects of single and sequential applications of mefluidide, maleic hydrazide, and ethephon alone or in combination with trinexapac‐ethyl (TE), on annual bluegrass seedhead formation. A secondary objective evaluated whether addition of TE enhanced the efficacy of ethephon while improving the safety on creeping bentgrass. Three independent studies were established on golf course greens during a 2‐yr period, with initial PGRs application before annual bluegrass seedhead formation. Regardless of PGR treatment, single or sequential applications in all studies showed no differences in annual bluegrass seedhead suppression. Ethephon‐containing treatments provided the best seedhead suppression with up to 95% reduction. No PGR treatments caused visible phytotoxicity to creeping bentgrass following single applications. Sequential applications of both mefluidide and maleic hydrazide caused significant phytotoxicity to creeping bentgrass for up to 3 wk after initial treatment (WAIT). With the exception of one evaluation date in the third study, tank mixture of TE with ethephon had little effect on annual bluegrass seedhead suppression. Tank‐mixing TE with ethephon marginally enhanced turf quality of creeping bentgrass up to 6% compared to ethephon alone.

Indaziflam is an alkylazine herbicide used for preemergence control of annual weeds in warm‐season turfgrass. Growth chamber studies were conducted to determine the effect of indaziflam rate on bermudagrass (Cynodon dactylon L. Pers.) shoot and root initiation as influenced by soil texture and organic matter (OM). Bermudagrass plants propagated from stolons were planted in five different growing media, including pure sand (100% sand), sand (92% sand, 6% clay) with or without OM (2%), and loamy sand (82% sand, 12% clay) with or without OM (2%). Indaziflam at rates of 48 or 16 g ha−1 followed by drenches of 2.5 cm of water were applied to the bermudagrass plants after maximal root length reached 30 cm. Bermudagrass growing in pure sand, regardless of indaziflam rate, showed the most injury, with root and shoot biomass reduced to <10 and <32%, respectively, compared with the nonherbicide‐treated control 38 d after treatment (DAT). Increase in clay content and addition of OM at 16 g ha−1 indaziflam significantly improved root biomass to ≥40% at 38 DAT. Despite inhibitions to root growth, aboveground tissues of plants growing in sand and loamy sand with OM showed minimal or no changes in turf color and coverage at 16 g ha−1 indaziflam. Results of this study indicate that small amounts of clay and OM in sandy soil aid in reducing bermudagrass phytotoxicity risk of 16 g ha−1 indaziflam.

Methiozolin is an herbicide with preemergence (PRE) and postemergence (POST) activities for control of annual bluegrass (AB; Poa annua L.). Previous research reported that fall applications provide better control than spring applications when methiozolin is applied as a POST, and PRE application appears to show a higher degree of efficacy than POST applications. Preemergence application for AB control on creeping bentgrass (CB; Agrostis stolonifera L.) putting greens requires treatment starting in late summer to early fall, when CB greens are likely under summer stress. Three field studies were conducted to evaluate the safety of fall sequential methiozolin applications on CB greens. Treatments consisted of methiozolin at 0.22, 0.45, 0.67, or 0.89 lb a.i./acre applied 1, 2, or 4 weeks apart, totaling 1.78 to 2.01 lb a.i./acre per season. Phytotoxicity was consistently observed in one out of three studies but was at an acceptable level (≥6 on a scale of 1–9) in all evaluations. Methiozolin applications, regardless of rate or application interval, resulted in a consistent AB control up to 95% over the season, compared with the nontreated control. Results suggest that sequential applications of methiozolin in fall with the initial treatment starting in late summer to early fall may provide effective AB control with acceptable safety to CB putting greens.

Annual bluegrass is a troublesome weed in golf course putting greens. The objective of this research was to evaluate creeping bentgrass putting green tolerance to bispyribac-sodium tank-mixed with paclobutrazol in the transition zone. Field trials with four replications were conducted in Oklahoma during 2009 and 2010 and in Missouri during 2010. The results of this study suggest that tank-mixing bispyribac-sodium with paclobutrazol may discolor creeping bentgrass putting greens but will not reduce turf quality below acceptable levels. Normalized vegetative difference index readings indicated no treatment differences in turf greenness at 4 and 8 wk after initial treatment. Weekly application of bispyribac-sodium at 12.4 g ha−1 or biweekly application at 24.8 g ha−1 alone or with monthly applications of paclobutrazol at 224 g ha−1 did not cause unacceptable injury to creeping bentgrass putting greens during the spring.