Grapevine, peach, and plum response to simulated florpyrauxifen-benzyl drift

Abstract

Off-target movement of rice herbicides is a concern in California, where sensitive crops are often grown nearby. Florpyrauxifen-benzyl and triclopyr are auxin-mimics commonly used in rice systems. To steward florpyrauxifen-benzyl around the time of its initial registration in the state, research was conducted to compare the onset of foliar symptoms from simulated florpyrauxifen-benzyl and triclopyr drift onto grapevine, peach, and plum. The rates were 1/200X, 1/100X, 1/33X, and 1/10X of the 29.4 g ai ha^–1 florpyrauxifen-benzyl and 1/200X, 1/100X, and 1/33X of the 420.3 g ae ha^–1 triclopyr rice use rates. Herbicides were applied on one side of one- to two-year-old peach and plum trees and one side of established grapevines in 2020 and 2021. The general symptoms for florpyrauxifen-benzyl and triclopyr were similar and included chlorosis, leaf curling, leaf distortion, leaf malformation, leaf crinkling, necrosis, and twisting on leaves. The symptoms from herbicides were observed on both sides of the grapevine canopy, whereas florpyrauxifen-benzyl symptoms on peach and plum were mostly observed on the treated side of the tree. Florpyrauxifen-benzyl and triclopyr symptoms were observed three days-after-treatment (DAT) for grapevines and seven DAT for peach and plum. In all crops, most symptoms persisted through 42 DAT. Some grape clusters showed deformation and dropping of berries. All treated crops gradually recovered during the season regardless of application rates. Because symptoms were relatively minor in peach and plum, this research suggested that application precautions that reduce off-site drift are likely to minimize the occurrence of significant injury. However, grapevines were more sensitive and showed injury symptoms up to 71% at 14 DAT with a 1/10X florpyrauxifen-benzyl simulated drift rate. Therefore, extra precautions such as using drift-management agents and proper wind speed conditions at the time of florpyrauxifen-benzyl applications may be necessary if there are nearby vineyards.