2018 ASHS Annual Conference

Lack of chill accumulation in pistachios has been a growing production issue in the California for the past several years. Growers have been facing crop losses as a consequence of these changes and there is a dire need to address this very important issue. This study hypothesized that some mechanical and chemical methods could be beneficial to compensate for lack of chill or to induce physiological changes in the trees so as to have a normal bloom and crop load. Fifteen-year-old pistachio trees of Kerman variety on UCB-1 rootstock were selected for this study at the California State University Campus in Fresno. The treatments included covering the trees with two type of shade netting (Black and Gray), spray of horticultural oils and kaolin clay dust. These treatments were compared with an unsprayed control over two years. Trees were covered by November 1 and the shade nets removed in late February both years. In the kaolin clay treatments, trees were sprayed with clay material throughout the winter months as and when need depending on rain events. The idea was to keep the trees covered throughout the chill accumulation period. Temperature and light intensity data were collected both inside and outside the shade netting using dataloggers. Chill accumulation was calculated using dynamic chill accumulation model as described by Glozer (2009). Data on bloom progression, nut growth, nut weight and volume, shell strength progression, yield and number of blanks were collected. The trees under oil spray bloomed significantly earlier than the trees under kaolin clay and shade netting treatments. Oil treatment trees were also ahead of other treatments in progression of nut growth and shell strength until the start of nut fill stage (Stage 3) of nut development. Oil and kaolin treatments resulted in significantly higher number of blanks. The treatments were not statistically significantly, different in terms of total yield or split in-shell percentage.