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 control mixed infestations of Western Flower Thrips (Frankliniella occidentalis) 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 consisting of abamectin 2.0% e.c. and abamectin tank-mixed with Pyrenone e.c. (6% pyrethrins, 60% piperonyl butoxide) reduced the mean number of thrips per blossom by 93.8% and 92.3%, respectively and were nonphytotoxic. 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 reduced 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°C for 15 and 20 s reduced the mean number of thrips per blossom by 88.1% and 95.3%, respectively. A 70% solution of isopropyl alcohol applied as a postharvest dip did not kill all thrips and was extremely phytotoxic to blossoms.