Effects of placement and distribution on the performance of granular formulations of insecticides for carrot fly control

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Abstract
Effects of granule distribution relative to carrot rows are discussed and further results described. Placing insecticides 5 to 10 cm deep 7.5 cm away from the centre line of the carrot row usually, but not always, improved their performance compared with bow‐wave applications. Both sides of the row need to be protected. The efficiency of chlorfenvinphos in a sandy loam, and phorate in a peaty‐loam, decreased with increasing distance from the row but they were slightly effective even 19 cm away. The optimum depth for side‐placing granules at sowing time varied from 5 to 10 cm, and combining side‐placement with a bow‐wave application did not greatly enhance efficiency. The most effective combination on a peaty‐loam was a bow‐wave application of 3 kg phorate/ha at sowing time followed 6 to 9 weeks later by a similar amount side‐placed 7.5 cm deep 7.5 cm from the row centre. Comparison of the performance of phorate broadcast, applied by the bow‐wave method or deep side‐placed indicated that efficiency was improved by restricting the granule distribution but that higher concentrations of granules were then needed in the treated zones to be equitoxic with more uniformly broadcast granules. Uptake by the carrot root system is an important factor in the action of insecticides against carrot fly larvae.

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