Horticultural mineral oil treatments in nurseries during aphid flights reduce Plum pox virus incidence under different ecological conditions

The application of horticultural mineral oil (HMO) treatments has been reported as a possible control strategy to reduce Plum pox virus (PPV) incidence in Prunus nurseries. The effect of Sunspray Ultrafine HMO at 1% on the natural viral spread was evaluated in experimental nursery plots of Nemaguard and Mariana GF8-1 Prunus rootstock blocks established under high natural inoculum pressure of the most prevalent PPV-types. Tests were conducted in experimental nursery plots in Plovdiv, Bulgaria (PPV-M and PPV-Rec), in Bistrita, Romania (PPV-D and PPV-Rec) and in LlSpain (PPV-D). Horticultural mineral oil treatments were applied weekly during the vegetative period from spring to fall (treatments were interrupted in the summer). Nursery plants were analysed yearly by double-antibody sandwich enzyme- linked immunosorbent assay with 5B-IVIA/AMR monoclonal antibodies. The population dynamics of the aphids visiting plants in each experimental nursery plot was monitored by the sticky-shoot method and also by Moericke yellow water traps. At all three locations, the aphid population first peaked in the springtime. Furthermore, a variable second peak of aphid population was observed in Plovdiv and Bistrita in autumn. The treatments reduced PPV incidence in the three experimental locations and plots and in both assayed Prunus rootstocks grown under high PPV-inoculum pressure. A reduction from 10% to 20% of PPV-incidence between treated and control plants (P <0.05) in Plovdiv and Bistrita, respectively, was observed at the end of the tests. However, HMO treatments did not prevent PPV infection altogether, probably because of the high PPV prevalence in the area near the experimental nursery blocks. The control of PPV in nursery blocks based on HMO is presented as an environmentally friendly strategy based on the physical action of the treatments.