Development and evaluation of a decision prediction tool for the reduction of fungicide applications for the control of strawberry powdery mildew epidemics

Abstract

Strawberry powdery mildew (Podosphaera aphanis) causes serious losses in UK crops, potentially reducing yields by as much as 70%. Consequently, conventional fungicide application programmes tend to recommend a prophylactic approach using insurance sprays, risking the development of fungicide insensitivity and requiring careful management relative to harvest periods to avoid residual fungicides on harvested fruit. This paper describes the development of a prediction system to guide the control of P. aphanis by the application of fungicides only when pathogen infection and disease progression are likely. The system was developed over a 15-year period on commercial farms starting with its establishment, validation and then deployment to strawberry growers. This involved three stages: 1. Identification and validation of parameters for inclusion in the prediction system (2004-2008). 2. Development of the prediction system in compact disc format (2009-2015). 3. Development and validation of the prediction system in a web-based format and cost-benefit analysis (2016-2020). The prediction system was based on the temporal accumulation of conditions (temperature and relative humidity) conducive to the development of P. aphanis , which sporulates at 144 accumulated disease-conducive hours. Sensitivity analysis was performed to refine the prediction system parameters. Field validation of the results demonstrated that to effectively control disease, the application of fungicides was best done between 125 and 144 accumulated hours of disease-conducive conditions. A cost-benefit analysis indicated that, by comparison with the number and timing of fungicide applications in conventional insurance disease control programmes, the prediction system enabled good disease control with significantly fewer fungicide applications (between one and four sprays less) (df=7, t=7.6, p =0.001) and reduced costs (savings between £35-£493/hectare) (df=7, t=4.0, p =0.01) for the growers.

Epidemiology and control of strawberry powdery mildew: a review

“…Both of these tools are useful to schedule fungicide treatments, thereby avoiding unnecessary applications (Lázaro et al, 2021). For SPM, several predictive models (Carisse et al, 2013a(Carisse et al, , 2013b and DSSs (Table 2) have been developed (Gubler et al, 1999;Eccel et al, 2010;Bardet and Vibert, 2011;Dodgson et al, 2021;Carisse and Fall, 2021;Fall and Carisse, 2022). However, the developed models, excepting that of Gubler et al (1999), have not been validated in different locations.…”

“…In the United Kingdom, a DSS implementing 15 years of historical data was developed by Dodgson et al, (2021). The model is based on laboratory and field evidence that P. aphanis, under optimum conditions (>15.5 and <30°C, 60% RH), takes 144 h (disease conducive hours) to complete a cycle from conidium germination (6 h) to growth of elongating secondary hyphae and sporulation (138 h).…”

“…When a fungicide application is made, the growers record this manually in the software, and reset the system to zero and the process repeats. Unlike the Carisse and Fall (2021) decision tree, the Dodgson et al (2021) model does not essentially require accurate estimation of susceptible leaves and airborne inoculum, and these variables are deemed to be limiting. Instead, the Dodgson et al (2021) forecast always assumes a standard presence of inoculum, and susceptibility for all crops.…”

“…Unlike the Carisse and Fall (2021) decision tree, the Dodgson et al (2021) model does not essentially require accurate estimation of susceptible leaves and airborne inoculum, and these variables are deemed to be limiting. Instead, the Dodgson et al (2021) forecast always assumes a standard presence of inoculum, and susceptibility for all crops. To effectively manage powdery mildew, growers are required to start each growing season with a clean-up spray treatment, as this was also confirmed by greater infection in crop where clean-up spray was neglected.…”

“…The model has been validated from 2009 to 2020 under tunnel conditions. To date, the Dodgson et al (2021) online real-time web-based prediction system is used and sold with commercial licencing (Strawberry Powdery Mildew Forecasting Model, Agri-tech Service, United Kingdom).…”