Increasing the efficacy of graminicides in wheat by gibberellic acid

Selective control of grass weeds in cereal crops such as wheat and barley always hasbeen a difficult task due to the taxonomic affinity between the crop and weeds. The selectivityof the currently used graminicides is not high enough to allow an increase in the herbicide ratein order to achieve adequate control of grass weeds, without causing severe damage to the crop.Most of the wheat cultivars grown today are dwarf or semi-dwarf, which are genetically notresponsive to exogenous gibberellic acid (GA) in stem elongation. We assumed that there is adifferential sensitivity toward GA between grass weeds and semi-dwarf wheat cultivars. Theaim of this study was to examine the possibility of improving the selective performance ofpostemergence herbicides in wheat and grass weeds by GA application. Pot experiments haveshown that GA applied prior to or simultaneously (as a tank-mixture) with postemergenceherbicides to two grass weeds,
Phalaris paradoxa and P. brachystachys,
resulted in asignificant increase in their sensitivity to foliar application of methabenzthiazuron anddiclofop-methyl. The GA-sensitive tall wheat cv. 'FA8193' responded to application of GA ina similar manner as the grass weeds and became more sensitive to postemergence applicationof methabenzthiazuron. The GA-insensitive semi-dwarf 'Lakhish' wheat cultivar, however, didnot respond to GA and remained tolerant to methabenzthiazuron. GA added to the spraysolution of several herbicides applied postemergence to semi-dwarf 'Bet HaShitta' wheatgrown in the field, did not alter the response of the crop to the herbicides,in indicating the potential of GA for improving herbicide performance and enabling lower herbicide input insemi-dwarf wheat crops.