John M. Peppers, James Harris, J. Scott McElroy
Abstract
Pinoxaden is a herbicide inhibiting acetyl coenzyme A carboxylase recently introduced for use in turfgrass. Currently, pinoxaden is labeled for use in all bermudagrass [Cynodon dactylon (L.) Pers.] and zoysiagrass (Zoysia spp.) turfgrass areas except putting greens. However, pinoxaden is only labeled for use in St. Augustinegrass [Stenotaphrum secundatum (Walter) Kuntze] sod production because of injury concerns. Tank mixtures of two or more herbicides can reduce injury to turfgrass species. Injury reduction can also occur when fungicides are tank-mixed with herbicides. Research was conducted between 2018 and 2019 to determine the effect that pinoxaden alone and tank mixtures of pinoxaden with one of two common fungicides, chlorothalonil and propiconazole, would have on four different cultivars of St. Augustinegrass: ‘Classic’, ‘Floratam’, ‘Palmetto’, and ‘Raleigh’. At the conclusion of the study, we determined that there is differential susceptibility to pinoxaden between cultivars of St. Augustinegrass and that both chlorothalonil and propiconazole have a safening effect on pinoxaden applications to St Augustinegrass, regardless of cultivar. The cultivars Classic and Raleigh were more susceptible to pinoxaden than Floratam and Palmetto. All four cultivars were less susceptible to pinoxaden when chlorothalonil and propiconazole were applied in combination with pinoxaden. These results suggest that pinoxaden can be applied in a tank mixture with either chlorothalonil or propiconazole to reduce pinoxaden injury to St. Augustinegrass. However, the effect that these tank mixtures may have on weed control is currently unknown.
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