FUMIGANTS FOR POSTHARVEST CONTROL OF INSECT PESTS OF CUT FLOWERS

Abstract

Fumigants provide a rapid means of disinfesting cut flowers to meet export requirements. Currently methyl bromide is used extensively for fumigating cut flowers and many other commodities. However, it is a potent ozone depletor and its use is being phased out in accordance with the Montreal Protocol, so alternative fumigants need to be found. One treatment currently used with a 2 h exposure period consists of a 10 s burst of Pestigas® (pyrethrum with carbon dioxide as a carrier gas) to agitate insects followed after 10 minutes by a 10 s burst of Insectigas®(dichlorvos with carbon dioxide as a carrier gas) as the main killing agent. However, the current Pestigas®/Insectigas® schedule is not fully effective against all pests encountered in flowers. Extending the fumigation period from 2 h to 4-6 h and increasing the dosage of dichlorvos from 0.1 g.m -3 to 1.7 g.m -3 improved the range of pests controlled but did not kill all eggs of Tetranychus urticae and left some larvae of Epiphyas postvittana and Strepsicrates ejectana severely affected (making small twitching movements and unable to feed). Assessment of several alternatives identified phosphine as the most promising fumigant because of its effectiveness against insects and its low phytotoxicity. Large scale trials are now being carried out in a commercial fumigation chamber using Pestigas® followed by Phosfume® (phosphine with carbon dioxide as a carrier gas). In our tests so far, phosphine appears suitable for registration for fumigation of cut flowers. Rcsults obtained in 6 h fumigations with 1.0-1.4 g.m -3 phosphine were at least as good as those obtained in 6 h fumigations with 1.7 g.m -3 dichlorvos.