The characteristics of mineral oils in relation to their inhibitory activity on the aphid transmission of potato virus Y
Abstract
In greenhouse trials paraffinic mineral oils, characterized by a viscosity gravity constant (VGC) of 0.790-0.819, and with viscosities between 12 and 30 cSt at 37°C (66-150 SUS) proved to have the best aphid transmission inhibiting activity of potato virus Y to red peppers. The activity decreased rapidly with decreasing viscosities but only slowly with increasing values.
Effective oils are fürther characterized by an unsulfonated residue (USR) of 95-100, indicating the near or total absence of aromatic structures, which are inactive and known to be phytotoxic. The paraffine-pourpoint should be below 0°C, indicating that n-paraffines do not form a very important part of the oil, since they are also inactive. Naphthenic structures seem equally inert, their percentage in the oil depending on the origin of the crude oil, because they cannot be separated from the paraffinic structures by refining procedures.
Mineral oils which one commercialize for agricultural practice normally have an USR above 95 and a paraffine-pourpoint below 0°C. Therefore, the information on the classification, based on a VGC value and on the viscosity, is already sufficient to allow an evaluation of those oils of their suitability as inhibitor of the virus transmission by aphids.