Evaluating the effectiveness of mineral oils in minimising the spread of non-persistent viruses in potato seed crops in GB

Four field trials were established in each of the three years of the project. The core treatments evaluated at three of the sites were:

• Untreated (control)
• Fortune (vegetable oil; @ 0.5% total spray volume)
• Olie-H (mineral oil; @ 3.1% total spray volume)
• Hallmark Zeon (75ml/ha)
• Hallmark/Fortune (Hallmark Zeon 75ml/ha + Fortune 0.5%)
• Hallmark/Olie-H (Hallmark Zeon 75ml/ha + Olie-H 3.1%)
• Hallmark/Biscaya/SumiAlpha/Tepekki
• Olie-H 3.1%/ Hallmark/Biscaya/SumiAlpha/Tepekki

The integrated programmes with sequences including more than one product were devised to evaluate the integration of potyvirus control with measures targeting colonising aphids and persistent virus transmission (Potato Leaf Roll Virus).

At the fourth site (Edinburgh), the aim was to investigate the effect on virus transmission and acquisition of applying Fortune and Olie-H to four varieties susceptible to the most prevalent potyviruses (PVY^N and PVA). Virus transmission was assessed by post-harvest virus testing of progeny tubers.

Evidence for oil-based treatments performing significantly better than the untreated (control) was observed in specific sites and seasons for PVA and PVY^N.  The report’s authors have concluded that mineral oil sprays applied from 50 – 75% emergence, or programmes with oil sprays included as part of the sequence can provide significant reduction of potyvirus transmission but under high infectivity pressure (vector and virus source) may not always provide the necessary levels of prevention of virus infection for Certified seed crops.

Oil application timing and dose rate will be restricted by the label requirements of the product selected. On most, but not all, current labels the latest timing of application for mineral oils is at tuber initiation.

Late blight control

Two field trials were established in each of the three years to compare the blight control achieved by commonly used blight control products with and without the addition of a mineral oil (Olie-H 3.1% of the spray volume). In 12 out of the 15 comparisons of the fungicides tested an improvement in foliar blight control was recorded.  However, the impact of oil added to fungicide on leaf blight was greatly influenced by the fungicide product used in the tank mix. Further details are provided within the report.