Control of the spread of tulip breaking virus in tulips with mineral-oil sprays

Several mineral-oil sprays used to curtail the spread of stylet-borne tulip breaking virus (TBV) in tulips ‘Elmus’ were tested. The similarly concentrated sprays prepared with summer oil, winter oil, Albolineum, and Asepthion oil, decreased the spread of TBV considerably. Control was improved by the more concentrated Albolineum sprays (2.5, 5, 10%), and spread was reduced more effectively, when variable quantities of emulsions providing good leaf coverage were used (2.5, 5%). The weight ratios of the bulb yields of plots given a 2.5% spray in all years and a 5% spray in 1972 and 1973 fluctuated closely (0–6%) around the value for the untreated plots, which was taken as 100. These ratios dropped by 11–19% after more concentrated sprays were used in variable quantities in 1971. Spraying was slightly more effective at weekly than at fortnightly intervals, but the weight ratios scarcely differed. Better control of TBV spread was obtained when spraying was started at the beginning of May; when started in June, the sprays were not effective. The weight ratios were not clearly influenced differentially except when spraying was begun in the first week of May. The efficacy of mineral-oil sprays is discussed in relation to tulips and lilies, with reference to comparable experiments. The application of mineral-oil sprays for curtailing TBV spread in commercial tulip culture is discussed.