Abstract
THE rapid progress in weed destruction made possible simply by introducing new chemicals has resulted in a concentration on obvious and gross effects. Examples of the selective toxicity of various chemicals between different plant genera and between different species of the same genus1 have been widely reported. Much less frequently cited are differential responses between varieties of one species. In potatoes, variation in varietal reaction to pre-planting application of trichloroacetic acid (TCA) has been noted2 and large differences in varietal susceptibility to 2 : 4-dichlorophenoxyacetic acid (2,4D) and 2-methyl-4-chlorophenoxyacetic acid (MCPA)3 have been found. Hayes4 has demonstrated the differential response of barley to DDT, susceptible varieties being killed by DDT application. Commercial varieties of sugar-cane differ in physiological tolerance to dalapon5. Fiddian6 gave evidence of differential susceptibility of cereal varieties to some commonly used herbicides, variation occurring in amount of leaf scorch, growth deformity, ripening retardation, ear malformation and spikelet sterility.
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