CONTROL OF THE SPREAD OF TULIP BREAKING VIRUS IN TULIPS WITH MINERAL-OIL SPRAYS

Control of the yearly spread was improved by the more concentrated Albolineum sprays (2.5, 5, 10%), which reduced TBV spread more effectively, when variably large quantities of emulsions were used (2.5, 5%), providing good coverage of the leaf surface. 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. They dropped by 11–19% after more concentrated sprays were used in variably large 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 in May; when started in June, the sprays were not effective. Distinctly, the weight ratios were not 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. Mineral-oil sprays, e.g. 5% Albolineum, may be considered suitable to curtail TBV spread in tulip culture, which means their use on all stocks until completion of the search for and roguing of diseased plants during the growing season and repeatedly on heavily infected stocks ultimately to be rejected endangering the health of neighbouring cultivars during the growing season as well as on stocks of non-flowering plant material and small stocks of newly bred cultivars.