Effects of carbonyl sulfide, methyl iodide, and sulfuryl fluoride on fruitphytotoxicity and insect mortality

Three potential chemical fumigants: carbonyl sulfide (COS), methyl iodide ( MI) and sulfuryl fluoride (SF) were tested at selected dosages on lemons ag ainst California red scale (Aonidiella aurantii) and MI and COS were tested on nectarines against codling moth (Cydia pomonella). In nectarines, COS w as tested at 0, 20, 40, 60 and 80 mg litre(-1), MI at 0, 10, 15, 20 and 25 mg litre(-1). Both fumigants intensified nectarine peel color, delayed frui t softening, but did not alter overall fruit quality. COS at 80 mg litre(-1 ) resulted in 87% codling moth mortality, but the fumigant dosage was insuf ficient to reach the desired probit 9 level (99.9968%). MI gave 100% codlin g moth mortality at 25 mg litre(-1). Lemons were treated with MI at 0, 10, 20, 40, 60 mg litre(-1), SF at 0, 10, 20, 40, 80 mg litre(-1) and COS at 0, 20, 40, 60 and 80 mg litre(-1). MI gave 100% red scale mortality at greate r than or equal to 40 mg litre(-1) but caused significant fruit injury. Con ditioning lemons at 15 degreesC for 3 days before MI fumigation lessened le mon phytotoxicity. Forced aeration at 3.5 standard litres per minute of lem ons for 24 h following MI fumigation at 20 mg litre(-1) significantly reduc ed phytotoxicity compared to 2 h postfumigation aeration after MI treatment . SF at greater than or equal to 40 mg litre(-1) gave 100% red scale mortal ity but resulted in commodity phytotoxicity. Lemons treated with the highes t selected dose of 80 mg litre(-1) COS gave only 87% kill of red scale, but failed to reach the desired probit 9 level.