Mechanical thinning trials conducted by Plant & Food Research, Marlborough since 2009 has resulted in positive outcomes for both fruit & trash removal and reduced incidence and severity of bunch rot (Botrytis). The heavy yields experienced in 2014 meant a large number of growers had to reduce crop loadings by up to 5<>15t/ha!
Machine thinning should be carried out shortly after fruit set, with the window of opportunity being 3 to 4 weeks. Key criteria is minimum berry size of 5mm or bunches of approx 50gms. Machine thinning needs to be completed before veraison.
Trash removal has been found to be a beneficial side effect of machine thinning where the action of the harvester greatly assists in removal of floral trash. Even in years where little or no fruit thinning is required, the harvester can be set up to remove floral trash only thus providing a reduction in incidence & severity of Botrytis.
Valley Harvesting supplied several harvesting machines for fruit thinning & trash removal in Jan 2014, 2015 & 2016. Each harvester is essentially configured as it would be for vintage, with the exception of a reduced number of beater rods installed. The amount of crop to be removed is calculated based on each grower/wine company yield estimates. A combination of beater and ground speed settings is then arrived at to achieve desired target yield reduction.
Unthinned fruit (left) with significant increase in incidence of Botrytsis compared with machine thinned (right)
