Oxysterol binding protein inhibitor (OSBPI) [Group 49] resistance management strategy

New strategy 2023, M. Christie and R. Beresford

Introduction

The purpose of this guideline is to help maximise the useful life of fungicides in the Fungicide Resistance Action Committee (FRAC) Group 49 for controlling plant diseases in New Zealand by providing relevant information about the nature of pathogen resistance to this group and guidance on practices that may prevent or reduce the development of resistance.

Disclaimer:

The fungicide and bactericide resistance information in the mode of action group table, the mode of action-based strategies and the crop-based strategies is intended to help manage the effects of pesticide resistance on plant disease control by agrochemicals in New Zealand. The New Zealand Committee on Pesticide Resistance (NZCPR) is a subcommittee of the New Zealand Plant Protection Society (NZPPS). The following parties: NZCPR, NZPPS, any people named in the strategies and any organisation the people may be affiliated with, do not guarantee that the resistance information is complete, consistent, accurate or up-to-date, or that resistance will not develop, or that the degree of resistance will decrease, as a result of the resistance information being used, and the parties accept no liability for loss or damage arising from the use of the resistance information contained in these strategies.

Product perspective

OSBPI fungicides are active against plant pathogenic oomycete fungi and used for the control of phytophthora diseases and downy mildews of numerous crops globally. Fungicide Resistance Action Committee (FRAC) information indicates that OSBPIs inhibit an oxysterol-binding protein homologue and oxysterol-binding proteins are implicated in the movement of lipids between membranes and other processes in the oomycete cell, such as signalling, maintaining cell membranes, and the formation of more complex lipids that are essential for the cell to survive.

The only OSBPI fungicide currently registered for use in New Zealand is oxathiapiprolin (Trade name, Zorvec® Enicade®), which is registered for the control of downy mildew (Peronospora destructor) in bulb onions. Another OSPBI fungicide, fluoxapiprolin, is currently under evaluation for use in New Zealand. Overseas, uses for OSBPIs include control of foliar oomycete diseases in grapevines, potatoes, tomatoes, cucurbits, lettuce, onions and sunflower, and phytophthora root diseases in citrus.

Current status of OSBPI resistance

FRAC indicates cross-resistance between oxathiapiprolin and fluoxapiprolin and resistance risk is considered to be medium to high. There appear to be no reports internationally of practical resistance to OSBPI fungicides, although pathogen isolates with reduced sensitivity have been found. Sensitivity to OSBIs has not been studied in New Zealand.

Resistance prevention strategy

This strategy is based on FRAC recommendations for Group 49 OSBPI fungicides.

Apply a maximum of 4 applications of OSBPI-containing products per year on the same acreage targeting the same pathogen.
Always apply in mixture with a fungicide from a different mode of action group. The mixing partner must be able to provide effective control of the target disease(s) at the rate and interval selected.
Always apply at full label rate and no more than three consecutive OSBPI-containing products.
Apply preventatively when disease risk is high and before disease has become severe.
OSBPI products must not be used in nursery production of crops grown from transplanted plants.

Implementation recommendations

Product labels for products containing OSBPI fungicides should include an appropriate statement about resistance management. This should be under the heading “Resistance Management” and indicate that the product contains a GROUP 49 oxysterol-binding protein inhibitor fungicide that is at risk from resistance development with details of how resistance risk should be managed.