UC Davis

Almonds (Prunus dulcis (Mill.) D. A. Webb) are essential part of the Californian landscape and economy. Their popularity in the last decades has increased drastically thanks to newer technological and plant-specific discoveries and developments. Their production is currently facing many challenges and to maintain their sustainable production, several changes must be made. The Almond Board of California has responded by developing strategies that would aid the sustainability of almonds in the near future. This thesis focuses mainly on dust abatement strategies by introducing off-ground harvest and the impact of fruit drop that might occur if current harvest process were to be altered. During 2019 and 2020, fruit drop (incorrectly referred to as ‘Windfall’) before harvest was found to be present in most of the orchards though it is was inconsequential in Nonpareil except under extreme conditions of drought or very delayed harvest. In later cultivars percent fruit drop (PFD) rarely exceeds 5% in the latest harvested cultivars and was markedly exacerbated by extended harvest delay or water stress. Fruit drop is highly correlated with the days past hull split at which harvest occurs (or the number of days fruit remains hanging from peduncle) and is exacerbated by water stress and equipment passes through the orchard. 2020 represented a ‘perfect storm’ for PFD with Covid and smoke delaying harvest, smoke exacerbating tree stress response, and limitations on water availability in many regions. When harvested at 15-20 days post hull split (5-10 days prior to current practice), windfall was less than 0.5% in Nonpareil and Independence and <3% in all but two orchards with late harvest cultivars. Since late cultivars represent just 25% of the planted trees the true impact of PFD on whole orchard productivity would be proportionately reduced. Further research is encouraged to better understand this phenomenon as well as the full costs and benefits of earlier harvesting.