Success of organic grapes in different vineyard conditions: yield and berry quality
Résumé
Grape production systems must adapt to reduce the quantities of pesticides used because of its
negative effect on environment. Organic viticulture may be one solution to face this issue. But to drastically
reduce pesticide use, innovative organic practices are required in every soil and climate conditions. In a context
of transition to Innovative Organic Viticulture (IOV), changing practices can strongly affect the agronomic
performances of grape production. In this study, we analyzed the performances of organic grape production
systems during the transition to IOV. Published methods are used to assess yield and grape quality. An
experimental network with 7 studied cases located in Northeastern and in Mediterranean area, in France, has
been set up since 2013. Each case was studied during three years of transition to IOV. The cases tested dealt
with conversion to organic or with introducing innovative practices in organic cases (Metral et al., 2012). In
Mediterranean area, the cases were planted with Grenache grapevine variety to produce Protected Designation
of Origin Côte du Rhône. In Alsace, the cases were planted with Riesling grapevine variety to produce
Protected Designation of Origin Alsace for two cases (CHA and ING) and Grand Cru Osterberg for the third
case (RIB). CHA case is a cooperative production; whereas all the other cases are private wineries. The results
support that most of the studied cases succeed in expected yield and grape quality for Protected Designation of
Origin wine production in very different soil and climate conditions. In all Alsace cases and in most of
Mediterranean cases, the yield ratios were satisfactory the 3-yeared of observation because estimated yield
match with target yield. The diminution of yield ratio in CHA matches with the winegrower goal. Indeed, the
winegrower introduced innovative practices to reduce yield together with drastically reduce copper fungicide
use. In Mediterranean area, three of the four cases have acceptable yield ratio (VERR, SERG and VIN). The
exception of year2 in VIN case is due to a regional pathogen accident: black-rot attack exploded in Rhone
valley and winegrower didn't manage to use pesticide to protect grapevines. The black-rot attack induced direct
loose of 64% of the VIN yield in year2. In year3, VIN strategy was a success to struggle against black rot: the
winegrower managed the pesticide use very precisely to avoid a too high lack of yield. GUE case never reached
the target yield. The winegrower strategy is ‘use zero pesticide’ and to accept yield loose. According to this, the
estimated yield is not so inacceptable in year1 and in year2. The exception of year3 in GUE case is due to the
same regional black-rot accident as VIN case in year2. Whatever the chosen innovative pesticide strategy, there
is still a huge risk of yield loose not depending in the case of a large fungi regional attack. The three years good
yield ratio of VERR and SERG cases is partly due to medium pathogens attacks. The quality results support
that most of the studied cases succeed in expected sugar rate according to the different PDO conditions. Just on
exception was observed: GUE sugar rate was the lowest. Maturity of berries was not reached even if yield ratio
satisfied the winegrower. In this study, we demonstrated that the success of organic grape production is
guaranteed in most of the studied cases. The target yield and target sugar rate are achieved in very different
vineyard areas conditions. Equally, year climate, latitude climate and PDO conditions are appropriated to
spread out Innovative Organic Viticulture.
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