POSTHARVEST TREATMENTS AGAINST WESTERN FLOWER THRIPS [FRANKLINIELLA-OCCIDENTALIS (PERGANDE)] AND MELON THRIPS (THRIPS-PALMI KARNY) ON ORCHIDS

Postharvest treatments, including insecticidal dips, isopropyl alcohol dips, insecticidal fogs and hot-water immersion, were evaluated to co ntrol mixed infestations of Western Flower Thrips (Frankliniella occid entalis) and Melon Thrips (Thrips palmi) on dendrobium orchid blossoms . The limiting factor for all postharvest treatments was phytotoxicity , characterised by a loss of vase life that differed among cultivars. Insecticidal dips and insecticidal fogs were less phytotoxic than hot- water immersion and isopropyl alcohol dips. Insecticidal fogs consisti ng of abamectin 2.0% e.c. and abamectin tank-mixed with Pyrenone e.c. (6% pyrethrins, 60% piperonyl butoxide) reduced the mean number of thr ips par blossom by 93.8% and 92.3%, respectively and were nonphytotoxi c. An insecticidal aerosol, Floragas (2% permethrin and 0.1% pyrethrum dissolved in high pressure liquified CO2) reduced thrips by 33% to 54 % with no phytotoxicity. Insecticidal dips for 3 min with agitation re duced the mean number of thrips per blossom by 43.7% to 99.1%. Of the 12 insecticides and one surfactant tested, only chlorpyrifos 44.4% e.c ., fluvalinate 22.3% f., and chlorpyrifos 50% d.f, were both effective and nonphytotoxic. Immersion in water at 49.5 degrees C for 15 and 20 s reduced the mean number of thrips per blossom by 88.1% and 95.3%, r espectively. A 70% solution of isopropyl alcohol applied as a postharv est dip did not kill all thrips and was extremely phytotoxic to blosso ms.