The contact activity of difenzoquat in two United Kingdom spring wheat cultivars

The contact action of difenzoquat was investigated on seedlings of spring wheat (Triticum aestivum L.) cultivars tolerant (Maris Butler) and susceptible (Sicco) to the translocated etTect of the herbicide on the apical meristem. Applied as a spray the chemical caused an increase in electrolyte leakage before the development of visible damage. Chlorophyll levels were also reduced and both effects were greater on Maris Butler than Sicco. Droplets of difenzoquat caused similar ultrastructural effects on the two cultivars. These included swelling of the chloroplasts with subsequent disorganization of the thylakoid system accompanied by disruption of other cellular components. Similar effects have been reported with paraquat and it is suggested that the contact action of difenzoquat is due to a weak paraquat type activity.