Powdery mildew in protected edibles: The challenge

Powdery mildew is a widespread global issue for both gardeners and commercial growers alike. Notably, the disease causes a significant loss of productivity globally, particularly in cucurbits and cereals, though it also has a large impact on ornamentals.

Infection is commonly identified by a white powder predominantly coating the upper surface of leaves, visually likened to an icing sugar dusting on a cake – but not the final flourish desired!

Podosphaera xanthii has been determined as the main cause of powdery mildew in cucumbers. It is a particular problem under protection, particularly in late summer and early autumn, as the hot, humid conditions of the glasshouse are a perfect environment for disease spread.

The application of fungicides is the conventional method of control. However, due to continuing loss of actives, research is needed to identify other actives and bioprotectants that could aid in the control of the pathogen. SCEPTREplus and Stockbridge Technology Centre delved deeper to help find answers to this persistent problem, using cucumber as a model crop within the protected edibles industry.

Research took place in the late summer of 2019 at STC on a cucumber glasshouse crop artificially inoculated with powdery mildew. A range of novel conventional and bioprotectants products were trialled and assessed for the efficacy of disease treatment. We also looked for the longevity of protection against the disease compared to the industry standard fungicide, Nimrod®, which is approved on-label until 2026.

The trial yielded some interesting results, with two novel conventionals achieving an 80% reduction in disease levels approximately three weeks after application.

Additionally, a bioprotectant was found to achieve a 65% reduction in disease levels with some efficacy two weeks after final application.

The trial was a success, and there is significant promise of some of these products being approved for use on protected cucumber in the UK, as approvals for the products already exist in other regions or on other crops in the UK. Some of these products may also be of interest for the treatment of powdery mildew in ornamentals.

This year we are looking further into the use of novel treatment strategies, compared to industry-standard practices, in the treatment of powdery mildew of Lonicera. Watch this space!