OSBPI Fungicides

Introduction and General Information

A FRAC OSBPI Working Group was formed in 2015 to generate common resistance management recommendations for the fungicide oxathiapiprolin and fluoxapiprolin.

Go directly to FRAC-Recommendations for Resistance Management for OSBPI Fungicides.

OSBP fungicides are active against oomycete fungi and used for the control of Phytophthora and downy mildews of numerous crops. OSBPIs inhibit an oxysterol binding protein (OSBP) homologue. Oxysterol binding proteins are implicated in the movement of lipids between membranes, among other processes. Inhibiting OSBP may disrupt other processes in the fungal cell, such as signaling, maintaining cell membranes, and the formation of more complex lipids that are essential for the cell to survive.

Oxathiapiprolin and fluoxapiprolin are cross-resistant.

OSBPIs have been classified under the FRAC Code 49. The resistance risk is medium to high.

FRAC Code Target site and code Group name Chemical group Common name Comments
49 F9
lipid homeostasis and transfer/ storage  		 OSBPI oxysterol binding protein homologue inhibition piperidinyl-thiazole-isoxazolines oxathiapiprolin

fluoxapiprolin		 Resistance risk assumed to be medium to high (single site inhibitor). Resistance management required. 

FRAC Recommendations for OSBPI fungicides

General Use Recommendations

(Reviewed January 2024)

  • Fungicide programs must deliver effective disease management. Apply OSBPIs at effective rates and intervals according to manufacturers’ recommendations. Effective disease management throughout the season is a critical component to delay the build-up and spread of resistant pathogen populations.
  • Apply OSBPIs only preventatively and in mixtures with effective fungicides from different cross-resistance groups.
  • The mixture partner should give effective control of the target disease(s) at the rate and interval selected.
  • Foliar exposure to OSBPI products should not exceed thirty-three percent (33%) of the total period of protection needed per crop. 

Specific Recommendations by Uses / Crops

The number of foliar applications of OSBPI products within a total disease management program must be limited as follows:

Grapes:

  • Make no consecutive applications of OSBPI fungicides.
  • Make no more than two (2) applications per season.
  • If the total number of applications targeting downy mildew is 4 or less, apply only one (1) application of OSBPI.
         

Potato:

  • Make no consecutive applications of OSBPI fungicides.
  • Make no more than three (3) applications per season.
  • If the total number of applications targeting late blight is 6-10, make no more than two (2) applications per season.
  • If the total number of applications targeting late blight is 5 or less, make only one (1) application per season.
  • In countries where OSBPI resistance has developed, make no more than two (2) applications per season.

   
All other crops:

  • Make no more than four (4) applications or maximum 33% of the total period of protection needed per crop, whichever is more restrictive.
  • Where the total number of fungicide applications targeting oomycetes is less than three (3), apply no more than one (1) application of an OSBPI product.
  • There should be no more than two (2) foliar applications of any OSBPI product per crop for the control of soil-borne pathogens.
  • Applications of OSBPI-containing products are to be made no more than two (2) times in sequence before applying a fungicide with a different mode of action. In areas where the agronomic risk is very high (e.g., continuous cucurbit cropping) and resistance has already been reported, further restrictions to the number of consecutive applications and alternation are recommended.

  • Where an OSBPI fungicide is used as a seed/soil treatment* then, as a precautionary measure, it should be counted as one of the permitted foliar OSBPI applications per crop.
  • The first foliar fungicide applied after an OSBPI seed/soil treatment* must not contain an active substance with the OSBPI MoA and must also provide satisfactory disease control against the fungal pathogen(s) targeted by the OSBPI seed/soil treatment*.
  • If needed, continue foliar application with alternating fungicidal MoAs for the remaining growing period.

          * directed stem sprays are interpreted as foliar not soil application

In case of non-cucurbit multiple crops, do not make more than six (6) foliar applications of OSBPI product per year on the same acreage or greenhouse, targeting the same pathogen.

Specifically, in the case of cucurbit crops, do not make more than four (4) applications per year on the same acreage or greenhouse, targeting P. cubensis.

OSBPI products must not be used in nursery production of transplanted agricultural crops.

Monitoring Results and Recommendations

At the annual meeting, the working group reviews the current year's monitoring results and decides whether they require changes be made to the next year's use recommendations.  The minutes of those meetings are below.