AN UNUSUAL OCCURRENCE OF THRIPS ON CASHEW

Although thrips have been recorded on the floral parts and foliage of cashewnut, the pest never assumed serious proportions particularly in the district of Ratnagiri where the crop is extensively grown. However, a very severe incidence of these two species was observed in the months of February and March, 1978. Nymphs and adults were found feeding on the tender portion of leaves, flowers, floral branches, nuts and apples. The rasping and feeding injuries made by thrips results in scabs on floral branches, nut and apples. The cracks were also observed on severely infested apples. Infestation on developing nuts results in the formation of shrivelled, corcky layer on the nuts resulting in malformation (Fig. 1) and immature drop. The affected nuts turned black in colour and were unattractive.

Observation on different cashew cultivars indicated that all cultivars, hybrids and the local types were found to be equally susceptible. About 10 to 15 nymphs and adults could be trapped in a wide-mouthed glass jar with a single finger tap on the floral branch. This indicated that a heavy population of thrips was present on the floral branches. Consequently about 20 per cent nuts developed a corcky layer on them at the time of harvest.

Application of 0.05 per cent endosulfan as spray given for tea mosquito control at the time of emergence of foliage, emergence of panicle and fruit set was not effective to prevent thrips infestation. Hence, an additional spray of 0.05 per cent quinalphos had to be given in order to control the pest.

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