Assessment of the tolerance of four cool season turf grasses to grass-killing herbicides with and without the addition of organosilicone surfactants

Abstract

Annual poa, Poa annua L.; browntop, Agrastis capillaris L. 'Egmont'; perennial ryegrass, Lolium perenne L. 'Seville' and Chewing's fescue, Festuca nigrescens Lam. 'Lobi' plants grown in pots were sprayed with twelve different herbicides at two rates with and without the addition of two organosilicone surfactants (Silwet L77 and S800) in March 1998. The most promising herbicides were tested again on the same species and cultivars in August 1998.

For some species there was a high degree of tolerance to certain herbicides irrespective of the rates used or the addition of an organosilicone surfactant. Chewing's fescue exhibited a high level of tolerance to haloxyfop, fluazifop-P-butyl, cethodim and sethoxydim, annual poa to sethoxydim and browntop to metsulfuron methyl.

For some species there was almost zero tolerance to certain herbicides and rates regardless of the addition of an organosilicone surfactant. Perennial ryegrass exhibited very low tolerance to sethoxydim, browntop to terbuthylazine at 1.5 kg a.i. ha⁻¹, annual poa to terbuthylazine at 1.5 kg a.i. ha⁻¹ and perennial ryegrass to chlorsulfuron at 300 g a.i. ha⁻¹.

For some species the addition of organosilicone surfactants decreased the tolerance to certain herbicides. Annual poa exhibited less tolerance to clethodim at 240 g a.i. ha⁻¹ with the addition of S800, perennial ryegrass to isoproturon at 390 g a.i. ha⁻¹ with the addition of either Silwet L77 or S800, perennial ryegrass to fluazifop-P-butyl at 375 g a.i. ha⁻¹ with the addition of Silwet L77 and perennial ryegrass to the combination of isoproturon at 1 kg a.i. ha⁻¹ and diflufenican at 200 g a.i. ha⁻¹ with the addition of Silwet L77. Conversely, for other species, the addition of a surfactant increased the tolerance to certain herbicides. Perennial ryegrass exhibited increased tolerance to terbuthylazine at 500 g a.i. ha⁻¹ and 1.5 kg a.i. ha⁻¹ with the addition of S800 (although this was less apparent in the second experiment), perennial ryegrass to isoproturon at 390 g a.i. ha⁻¹ with the addition of S800, annual poa to haloxfop at 150 g a.i. ha⁻¹ and 300 g a.i. ha⁻¹ with the addition of either Silwet L77 or S800, and perennial ryegrass to the combination of isoproturon at 1 kg a.i. ha⁻¹ and diflufenican at 200 g a.i. ha⁻¹ with the addition of S800 (less apparent in the second experiment).

Of the herbicides and organosilicone surfactants tested, haloxyfop at 150 - 300 g a.i. ha⁻¹ without the addition of an organosilicone surfactant was identified as the best option for controlling annual poa in Chewing's fescue turf, terbuthylazine at 500 g a.i. ha⁻¹ either alone or with the addition of S800 at 0.1% (v/v) as the best option for controlling annual poa in perennial ryegrass turf, and glyphosate at 180 g a.i. ha⁻¹ with the addition of Silwet L77 at 0.25% (v/v) as the best option for controlling annual poa in browntop turf These herbicides should undergo field testing to ensure they are safe to use on high value turf areas.