Differential tolerance and selectivity of herbicides in forages of the genus Cynodon

Abstract

Plant recovery due to herbicide symptoms of phytotoxicity characterizes an additional waste of energy that should not be accepted as a natural physiologic response; therefore, it might result in yield losses. Herbicide‐tolerant forages and the use of less phytotoxic products on pastures provide improvements in chemical weed control and increases in forage yield. The objectives of this study were to test differences between Tifton 85 (Cynodon spp.) and African star grass (Cynodon nlemfuensis) in relation to their degree of tolerance to herbicides, as well as the selectivity of herbicides for both species. The experimental design was completely randomized, in a 2 × 8 factorial, with four replicates. Two species of Cynodon and eight herbicide treatments were evaluated. The tolerance and selectivity of herbicides for Tifton 85 and African star grass are a function of each species and the type and dose of herbicide applied. Among the two species of Cynodon, Tifton 85, in general, was more tolerant to the applied herbicides than was the African star grass and consequently with less probability to occur forage yield losses. The most phytotoxic herbicides for both forages were fluroxypyr + aminopyralid (160.0 + 80.0 g ae/ha [grams of acid equivalent per hectare]), fluroxypyr + triclopyr (320.0 + 960.0 g ae/ha) and glyphosate (180 g ae/ha). The most selective herbicides were bentazon (720.0 g ai/ha [grams of active ingredient per hectare]), imazapyr (25.0 g ai/ha) and MSMA (1,440.0 g ai/ha), which have potential for use in fields of Tifton 85 and African star grass.