Control of field spread of non-persistent viruses in flower-bulb crops by synthetic pyrethroid and pirimicarb insecticides, and mineral oils

The ability of liquid formulations of synthetic pyrethroid insecticides, a carbamate insecticide, and mineral oils, to limit the spread of non-persistent viruses in lilies, tulips, hyacinths and bulbous irises, was studied under field conditions that favoured rapid virus spread. Bait plants were sprayed and virus source plants were not. Substantial control was consistently achieved by weekly sprays of pyrethroids in moderate amounts of active ingredient. No significant additional control was obtained by increasing rates of application, whereas at low rates the control was inadequate or very variable. Control was generally improved by spraying twice a week, whereas fortnightly spraying was inadequate. Fenvalerate sprays gave slightly better control than permethrin in lilies and bulbous irises. The carbamate insecticide gave inconsistent or no control. Pyrethroids were on average only half as effective as mineral-oil sprays. Application of pyrethroids, unlike that of oil sprays, did not reduce bulb yields. The use of pyrethroids to affect probing behaviour of aphids, and consequently its potential to limit the spread of non-persistent viruses in ornamental bulb crops, is discussed.