Effect of the timing of insecticide applications on infestation by Cavariella aegopodii Scop,on carrots*

The residual effectiveness of demeton-methyl and menazon sprays applied to carrot plants was compared in the laboratory using Cavariella aegopodii Scop, and more observations were made in the field, where applications of both insecticides were timed in relation to the observed immigration period of the aphid. The relative field performances confirmed those found in the laboratory and, as the aphid population control exercised was inversely proportional to the amount of alate immigration occurring after the sprays had become ineffective, the more persistent menazon was progressively superior to demeton-methyl the nearer they were applied to the beginning of immigration. A single spray application of either material towards the end of immigration gave a similar overall control of aphid numbers to that given by disulfoton granules applied at sowing time. To minimize colonization, two spray applications spanning the immigration peak were required and, with 2 weeks between the demeton-methyl sprays and 3 between those of menazon, the highest degree of control was obtained when the first application was made 7–10 days after the beginning of immigration.