On-Farm Trials Reveal Significant but Uncertain Control of Botrytis cinerea by Aureobasidium pullulans and Potassium Bicarbonate in Organic Grapevines.

Anabelle Laurent,Séverine Dupin,David Makowski,Fernando E Miguez,Nicolas Aveline

doi:10.3389/fpls.2021.620786

Abstract

Botrytis cinerea, a fungal pathogen that causes gray mold on grapes, can decrease yield, substantially reduce wine quality, and therefore cause significant economic losses. In a context of increasing awareness of environmental and human health, biopesticides are a potential alternative to synthetic chemical treatments to produce grapes and wine in compliance with high food standards. However, the effectiveness of biopesticides is not well known and more research is needed to help winegrowers assess their ability to control wine diseases. Our study aims to assess the efficacy of two commercial biopesticides, based on potassium bicarbonate and Aureobasidium pullulans, in reducing the incidence of gray mold (i.e., the proportion of grape bunches that are diseased). We use data from an on-farm trial network managed over 3 years (from 2014 to 2016) in a major wine producing region located in Southwestern France, and fit Bayesian generalized linear multilevel models able to take the variability of treatment effect across trials into account. The fitted models were then used to estimate the efficacy on incidence as a function of the severity (i.e., the proportion of diseased grape berries in a bunch) in an untreated plot in order to determine if the effectiveness of the treatments depends on the disease pressure. At average disease severity (i.e., 3%), the efficacy on disease incidence at the network level was equal to 20% [95% CI = (−0.1; 37.3)] and 13% [95% CI = (0.2; 24.7)] for potassium bicarbonate and A. pullulans, respectively. For both biopesticides, the efficacy on incidence for a new site-year is highly uncertain, but potassium bicarbonate had a lower uncertainty and a lower application cost compared to A. pullulans. Our results confirm that potassium bicarbonate is an interesting biopesticide under farming conditions in organic vineyards in southwestern France, but the amount of uncertainty points to the need for further research.

Highlights

Reducing the use of synthetic pesticides has become a major objective in Europe, in France, where their use has remained at a high level for many years despite government actions (Hossard et al, 2017)
Our objective is to evaluate whether the two abovementioned biopesticides are effective in controlling the incidence of gray mold in commercial vineyards and whether their efficacy depends on the disease severity in untreated controls
Observed mean disease incidences in treated and untreated bunches varied between trials for both biopesticides (Figure 1)

Summary

Introduction

Reducing the use of synthetic pesticides has become a major objective in Europe, in France, where their use has remained at a high level for many years despite government actions (Hossard et al, 2017). Synthetic pesticides are used several times a year to control various diseases caused mostly by pathogenic fungi (Chen et al, 2019). This crop accounts for around 14% of product purchases for less than 4% of the agricultural area occupied (Butault et al, 2011). The intensive use of synthetic pesticides has negative consequences on the environment by contaminating soil, surface and ground water (Komarek et al, 2009; Mailly et al, 2017), and on human health (Coleman et al, 2012; Chen et al, 2020). There is a need to test biopesticides under field conditions to assess their actual effectiveness and adapt control strategies against gray mold in vineyards (Nicot, 2011; Pertot et al, 2017a)

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