Decision aid to support the use of curative late blight fungicides
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Date
04/07/2020Author
Maloney, Kyran
Metadata
Abstract
Late blight, caused by the oomycete pathogen Phytophthora infestans (Mont.)
de Bary remains a severe threat to potato production in temperate regions and
necessitates a high volume of fungicide inputs. A recent focus of research has been
to improve the application of Integrated Pest Management (IPM) principles to the
control of late blight. Extensive monitoring programmes and warning systems are
currently delivered via online platforms, and growers also have access to
information on fungicide properties and the relative resistance of different cultivars
to the pathogen. Growers and agronomists would benefit from additional tools
which aid the decision-making process and allow improved integration of available
control strategies.
A strong example of this is the use of curative fungicides. Fungicides which can
act curatively (within the incubation period of pathogen development) are an
increasingly important component of late blight control, and there is scope to
improve their deployment. The aim of this study was to produce a simple decision
aid that can be used by growers and agronomists to inform their decision to use a
fungicide with curative properties following weather conditions associated with a
high risk of infection. Guidance available before the development of this decision
aid was somewhat subjective, and did not take into account factors that may modify
the efficacy of curative fungicides for which there is very little published
information.
Several contemporary P. infestans isolates were characterised in this study for
their growth rates, both visually and sub-clinically using a qPCR assay. These data
were then used to test a range of potential pathogen growth models which have
been used by previous authors to model temperature-dependent growth in other
biological systems. Many of these models provided good descriptions, and the best
performing was used to predict pathogen development with the decision aid.
Characterisations of the curative effect for a representative curative fungicide
(propamocarb-HCl + fluopicolide) were generated for selected isolates in both
laboratory assays and under field conditions. Within the laboratory bioassay, more
frequent sampling (4 hour intervals) than is usually reported in experiments of this
nature was used to assess the nature of the curative effect over a time frame of up to
72 hours post inoculation. Curative control declined rapidly with increasing
pathogen development, with the relationship best described by a logistic function.
This function, and the parameters generated from the bioassays, were used within
the decision aid to predict the likely outcome of curative treatments.