Improved timing of curative blight fungicides for superior control of late blight and greater cost effectiveness 


In the UK potato growers have access to many fungicides with chemically diverse active ingredients (a.i.s). This is crucial for successful late blight management as plant protection products can be selected to match the growth stage of the crop, or the local disease pressure. The availability of many late blight active ingredients with different modes of action (FRAC, 2018) is also key to sustainable control by helping to minimise the risk of the development of insensitivity. All blight fungicides are protectant, but several active ingredients also have curative activity (i.e. they are active post infection but before the development of symptoms), this is often referred to as 'kickback' activity. Optimal timing of curative fungicide use will provide better, more sustainable and more cost-effective control of late blight.

Summary of Results

  • Methods were developed to quantify curative activity more completely than have previously been reported.
  • Taking account of post-infection temperature and also modelling pathogen development provided a better prediction of curative control than considering only the chronological time between infection and treatment.
  • Field experiments in which natural infection was simulated demonstrated that elevated cultivar resistance increased the magnitude of the curative effect and/or extended the curative window.
  • A strong relationship between documented 1 to 9 resistance ratings for cultivars and the rates at which P. infestans colonises leaf tissue was demonstrated across 16 cultivars.
  • A simple decision aid for growers and agronomists, which can be used as a guide as to whether or not a curative a.i. is required for any scheduled fungicide application, was developed. Data for the most aggressive 13_A2 isolate were used as the basis of the decision aid.
  • The decision aid indicated that the impact of post-infection temperature on curative efficacy was considerably greater over the temperature range 6 to 18 oC than 18 to 26 oC.
  • Very limited validation of the decision aid using field data provided mostly good predictions, but with some biases. Much greater validation is suggested, most probably leading to model refinements.
Project code:
01 October 2014 - 30 September 2017
Project leader:
Ruairidh Bain


115R486 Curative Fungicides Final Report