Can Mineral Oil Protect Seed Potato Against Aphid Transmission of Potato Virus Y?

Potato virus Y (PVY) is a limiting factor for the production of certified seed potato in Tunisia. PVYNTN is the most important reason for downgrading seed potato lots of variety Spunta to lower classes and for rejection during certification. Transmission efficiencies of aphid species for different PVY strains are established for the most abundant ones. In total about 15 aphid species are known to be vectors of PVY with different efficiencies. There are five aphid species that colonize potatoes: Aphis gossypii, Macrosiphum euphorbiae, Myzus persicae, Aphis fabae and Aulacorthum solani. Eleven other aphid species that do not colonize potatoes seem to be far more important in PVY transmission: Aploneura lentisci, Brachycaudus helichrysi, Brachycaudus cardui, Hyalopterus pruni, Hyperomyzus lactucae, Acyrthosiphon pisum, Rhopalosiphum padi, Rhopalosiphum maidis, Aphis spiraecola, Cavariella aegopodii and Lipaphis erysimi. Therefore, to limit PVY propagation insecticide sprays are used to control aphids. However, intense use of aphicides has led to the selection of resistant aphid populations. As an option for PVY control, a few alternatives are available for seed potato production, among them mineral oil whose efficacy has been widely reported. Nevertheless, the use of mineral oils for agricultural aphid management is still very limited in Tunisia, probably due to the tendency of seed growers to believe that oils may cause: (i) phytotoxicity (while this is a problem only when oils are used with fungicides); and (ii) the loss of yield. Noting this problem, we evaluated a strategy consisting of use of oil to reduce aphid multiplication and to protect plants against aphids. This chapter compares the effect of mineral oil with and without insecticides on PVY infection. Results indicate that infectious aphids cannot transmit PVY in plants with oil in the laboratory, and also that healthy aphids cannot acquire viruses on oil-treated plants infected by PVY. Oil treatment of infected plants limited PVY propagation to 2.5% while plants not treated with oil showed a level of 9.5%. Finally, there were no significant yield losses in potato plots treated with oil (with yields of 0.28-0.33 kg per plant) compared with non-treated plots (yields of 0.26-0.30 kg per plant) under field conditions. This work illustrates that the bias farmers have against oils as an option for control of aphids is unfounded.