Control of air-borne field spread of tulip breaking virus,lily symptomless virus and lily virus X in lilies by mineral oils,synthetic pyrethroids,and a nematicide in the Netherlands

The inhibitory effect on the spread of viruses in lilies viz., tulip breaking virus (TBV; nonpersistently aphid-borne, potyvirus,) lily symptomless virus (LSV; non-persistently alphidborne, carlavirus), and lily virus X (LVX; potexvirus of unknown etiology), was studied of brands of mineral oil (Luxan oil H and Duphar-7E oil) and synthetic pyrethroid insecticides (l-cyhalothrin and deltamethrin), and a nematicide (aldicarb) in crops in which virus-infected plants were present as virus sources. The spread of TBV and LSV were controlled by sprays of mineral oil and insecticide, while that of LSV was also limited by the soil-applied nematicide. The spread of LVX was reduced by the insecticides and, not effectively by the mineral-oil spraying, by which data the mode of transmission may be presumed to be by an insect in the persistent or semi-persistent manner.Mixtures of mineral oil and pyrethroid were more effective in the reduction of spread of TBV and LSV than either components tested alone. The mineral oil was the most effective component in the mixtures in which pyrethroid added a slight extra effect. The addition of pyrethroid did not mask either the lower efficacy of the oil brand Duphar-7E oil, or the diminished inhibitory effect of low dosages of oil. The normal rate of mineral oil gave similar control to that of a mixture of mineral oil at half rate plus the pyrethroid at full dosage. Low rates of oil, or even synthetic pyrethroids alone may be used on cultivars which suffer of the loss of bulb weight by the use of normal or decreased rates of oil. Weekly sprays were more effective than fortnightly sprays. The rate of control by the weekly sprays ranged between 90 and 95% for Luxan oil H at half dosage plus the full rate of pyrethroid. Weekly sprayed synthetic pyrethroids alone onto the virus sources and the plants to be infected gave 60–70% control. The weight ratios tended to be slightly reduced if the half dosage of the efficient Luxan oil H was used. Factors which affect the control of the air-borne field spread of viruses by mineral oils and synthetic pyrethroid insecticides in lilies are discussed.