Selectivity of Cyhalofop-butyl in Poaceae Species.

Abstract

Responses to foliar-applied cyhalof op-butyl of the seedlings of 29 Poaceae species at about 3- to 4-leaf stage were examined. Species belonging to subfamilies of Panicoideae, except for Imperata cylindrica, and Eragrostoideae were all susceptible, being completely controlled at 100g ha-1. Most of these species are important summer weeds in crops. Alopecurus aequalis (Pooideae) and Agrostis alba (Pooideae) were also susceptible. Six of 10 other Pooideae species and the two Oryzoideae species tested, as well as I. cylindrica, in which all treated plants survived at 300g ha-1, were shown to have tolerance to cyhalofop-butyl. The other four Pooideae species were less susceptible and incompletely controlled at 100g ha-1. Oryza sativa displayed the highest tolerance; plants treated at 300g ha-1 did not show any significant differences from untreated plants. The typical visual symptom common through all plants of affected species was withering of the emerging leaves. The critical response that led to plant death, however, appeared to be the suspension of new growth. Plant survival after this phase seemed to depend on whether new development was restored before unaffected leaves lost their activity, by resumption of healthy leaf emergence mainly by formation of tillers or rhizomatous shoots.