Clethodim and photosystem inhibitors on sourgrass control as a function of application time¹

This study aimed to evaluate the effects of application time and addition of diuron to clethodim and diquat on the control of sourgrass. Two experiments were conducted with sourgrass plants, applying spray solutions comprising the herbicide clethodim (216 g a.i. ha^-1), clethodim + diquat (216 + 400 g a.i. ha^-1), and clethodim + diquat + diuron (216 + 400 + 400 g a.i. ha^-1) three times (08:00, 12:00, and 16:00) in addition to the control. Control and mass evaluations of sourgrass plants were performed in both experiments, and the relative rate of linear electron transport by PSII and leaf accumulation of hydrogen peroxide were evaluated in the greenhouse experiment. The results indicated an increase in sourgrass control with the addition of diuron to the mixture, resulting in 100% control in the application performed at 16:00. Spray solutions containing photosystem inhibitors should be applied at 08:00 and 16:00 to improve plant control. These mixtures applied under lower light intensity showed greater inhibition of the relative electron transfer rate and increased H₂O₂ concentrations with greater accumulation of this reactive oxygen species (ROS; 17894.17 nmol g^-1 FM) after the application of clethodim + diquat + diuron at 16:00. The addition of diuron was necessary for total plant control, resulting in greater inhibition of photosynthetic activity and accumulation of ROS.

Key words
Digitaria insularis (L.) Fedde; Oxidative stress; Graminicides; Tank mixture; Bipyridyliums.