The experiments were designed to evaluate the impact of two mineral oils: Sunspray 850 EC (85% of mineral oil) and Sunspray Ultra-Fine (98.8% of mineral oil) applied for a prolonged time (2 vegetation seasons) on yields of tulip of ‘Leen van der Mark’ cv. Tulips were treated 3 times (since the mid of April till the beginning of May) at weekly intervals with the oils at concentrations: 1.0, 1.5, and 2.0%. The oil preparations used at concentrations 1.0–1.5% had no negative influence on stem and tepals lengths at tulips grown in the field. No phytotoxicity symptoms on stems nor leaves were found. On plots protected with mineral oils, percentage of virus-infected plants was lower than for control, while high efficiency was recorded only in 2011 when using Sunspray 850 EC at 1.0–2.0% concentration. The oil preparations applied for a prolonged time at concentration of 2.0% caused a decline in commercial and the first choice bulb yields. No negative sequential effects of oils on quality of obtained flowers during tulip forcing in a greenhouse, was observed. The efficiency of mineral oils in reducing the virus spread evaluated based on the number of virus-infected flowers during forcing in the greenhouse depended on the year of study and type of the oil. The best results were achieved applying Sunspray 850 EC at concentrations of 1.0–1.5%. Oil preparations can be safely applied for tulip cultivation for a prolonged time if concentration does not exceed 1.5%. Despite of positive effects in reducing the virus spread in the field growing and forcing, three spraying treatments using mineral oils during vegetation season did not ensure a complete plant protection against viral infections.

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