Pyrimisulfan is a sulfonanilide herbicidal inhibitor of ALS with structural similarity to bispyribac-sodium and pyrithiobac-sodium (Asakura et al., 2012). Pyrimisulfan is used for both pre- and postemergence weed control in rice (Oryza stricta L.) paddy fields (Yoshimura et al., 2013). Applications of pyrimisulfan at 50 to 75 g·ha−1 effectively controlled Echinochloa spp., rock bulrush (Schoenoplectus juncoides), pickerel weed (Monochoria vaginalis), and Lindernia spp. in greenhouse trials (Asakura et al., 2012).
Reduced efficacy of pyrimisulfan formulated as a “wettable” powder under flooded conditions common in rice production spurred the development of a controlled-release granular formulation (0.67% pyrimisulfan) designed to control weeds both pre- and postemergence (Asakura et al., 2012). A series of greenhouse experiments were conducted in Japan to compare weed control efficacy of this controlled-release granular formulation to a granular formulation of bensulfuron-methyl (0.75%) + bromobutide (9%) + pentoxazone (2%) + pyriminobac-methyl (4.5%) that is a standard herbicide used by Japanese rice producers (Asakura et al., 2012). Herbicides were applied at 10 kg·ha−1 both pre- and postemergence with and without simulated flooding. Granular pyrimisulfan controlled 16 different weed species 96% to 100% when applied preemergence, including biotypes of pickerel weed and rock bulrush with target site resistance to sulfonylurea herbicides. Similarly, granular application of pyrimisulfan at an early postemergence timing (two to three leaves) controlled seven different weed species 90% to 100%, including two biotypes with confirmed resistance to sulfonylurea herbicides. Flooding did not affect efficacy of granular pyrimisulfan in either experiment whereas the standard of bensulfuron-methyl + bromobutide + pentoxazone + pyriminobac-methyl showed reduced efficacy for control of tidalmarsh flatsedge (Cyperus serotinus Rottb.), Scirpus nipponicus Makino, cosmopolitan bulrush [Bolboschoenus maritimus (L.) Palla], pigmy arrowhead (Sagittaria pygmaea Miq.), and threeleaf arrowhead (Sagittaria trifolia L.) under flooded conditions.
Penoxsulam is an ALS inhibitor used for broadleaf weed control in managed turfgrass systems (Loughner et al., 2006). Penoxsulam provides early postemergence control of weeds such as white clover (Trifolium repens L.), buckhorn plantain (Plantago lanceolata L.), common dandelion (Taraxacum officinale L.), ground ivy (Glechoma hederacea L.), and virginia buttonweed (Diodia virginiana L.) at rates of 20 to 180 g·ha−1 (Loughner et al., 2006). Interestingly, weed control efficacy of penoxsulam applied on a granular fertilizer carrier (average particle size, 0.5–2.5 mm) exceeded applications formulated as liquids (Loughner et al., 2006). Penoxsulam is often applied in combination with other herbicides to widen the spectrum of weeds controlled by a single application. For example, Loughner and Nolting (2010) evaluated efficacy of penoxsulam + 2,4-D + dicamba (LockUp; Dow AgroSciences, Indianapolis, IN) for control of white clover and common dandelion at six locations in the northern United States over 2 years. The researchers found that the presence of foliar moisture at application increased efficacy. Synergy has been observed when combining penoxsulam with other ALS-inhibiting herbicides as well (Hufnagl and Mann, 2015).
Weed control efficacy of granular pyrimisulfan is limited to grassy weed and tuber species of rice (Asakura et al., 2012). Penoxsulam is an effective option for early-postemergence control of broadleaf weeds (Loughner et al., 2006). Considering that both pyrimisulfan and penoxsulam efficacy are improved when applied on a granular carrier, combining pyrimisulfan with penoxsulam may provide turfgrass managers a new option for broadleaf and sedge weed control in warm-season turfgrass. Hoyle (2017) reported that pyrimisulfan + penoxsulam was safe for use on both buffalograss (Bouteloua dactyloides, cv. Cody) and zoysiagrass (Zoysia japonica, cv. Meyer), and effectively controlled large crabgrass (Digitaria sanguinalis). However, there are no published reports on sedge and broadleaf weed control efficacy of pyrimisulfan + penoxsulam in warm-season turfgrass. We hypothesized that pyrimisulfan + penoxsulam could effectively control white clover, yellow nutsedge, wild violet (Viola spp.), ground ivy, and virginia buttonweed when applied at an early-postemergence growth stage. Several field experiments were conducted during 2017 and 2018 to test this hypothesis.
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