Recovery of grain sorghum [Sorghum bicolor(L.) Moench] from atrazine and cyanazine phytotoxicity

Recovery of growth following atrazine and cyanazine toxicity and the effect on subsequent grain yield of sorghum were studied in nutrient solutions in two separate experiments. In Experiment I, concentrations of atrazine and cyanazine were decreased at weekly intervals based on halflife values of 60 and 15 days respectively. Cyanazine was initially more toxic to sorghum than atrazine. By the termination of the experiment cyanazine-treated plants had recovered better and outyielded atrazine-treated plants. Although significant yield reduction resulted in all treatments, the degree of initial toxicity was not necessarily reflected in grain yield. In Experiment II, sorghum was exposed to atrazine for periods of 1, 2, 4, 8, 12 and 16 weeks before returning to atrazine-free solutions. Grain yields were reduced significantly in all treatments except where sorghum was exposed to atrazine for one week only. Recovery was a function of the degree and persistence of toxicity. Grain yield reduction was associated with the commencement of recovery after the differentiation of the growing point to the reproductive phase. S. Afr. J. Plant Soil 1985, 2: 146–150