Selective phytotoxicity of soil Applied Type Herbicides towards Cool-Season Turfgrasses and Poa annua L.

Abstract

Susceptibilities of three cool-season turfgrasses, kentucky bluegrass (cv., Hunts Ville), tall fescue (cv., Falcon) and perennial ryegrass (cv., Kentucky-31), to ten soil applied type herbicides sprayed at pre-seeding, pre-emergence, post-emergence (1L stage) and after cutting were evaluated by pot tests in greenhouse, and ED10 values, which indicate dosages of the herbicides for 10% reduction of plant heigh, were obtained. In addition, susceptibilities of Poa annua L. to the herbicides applied at pre-emergence were determined, and ED90 values which indicate the dosages of the herbicides for reducing the dry weight of the above-ground parts of the weeds by 90% were obtained in a simiar manner. Relative selectivity of these herbicides towards the turfgrasses and Poa annua L. were then discussed in terms of ED10 /ED90. The results obtained were summarized as follows.
Selective phytotoxicity of each herbicide was shown in Figs.1 to 10. Bensulide were highly selective to all the turfgrasses even at the 1L stage, and the others showed higher selectivities to perennial ryegrass rather than to kentucky bluegrass. In general, selectivity of the herbicides increased with developing growth stage of the turfgrasses, and the highest selectivities were observed when applied after cutting.
Accordingly, it was suggested that bensulide can be used safely for the control of Poa annua L. in the three cool-season turfgrasses, and that acephenone and benfluralin can also be used safely in tall fescue and perennial ryegrass, when the turfgrasses have grown up to the 1 L stage before spray.