A study on the efficacy of hydrogen cyanamide and winter oil applications on male and female pistachio bloom and yield

M. Khezri
Erratic flowering and bloom asynchrony of male ‘Peters’ and female ‘Kerman’ trees have been observed in low to marginal chill years in growing regions of the Central Valley, California. In this study, the efficacy of hydrogen cyanamide (Dormex®) was sprayed as a rest breaking agent (RBA) was compared to winter oil after different chill portion accumulation. Oil (oil440, 6% v/v) and hydrogen cyanamide (Dormex®, 4% v/v) were sprayed at different chill portions (CPs) on ‘Kerman’ and ‘Peters’ pistachio trees in three field locations in Tulare County, California. One of these field was located in low winter chill area (CP≤60) and the other two fields were at CP≥65. Also, oil (oil440, 6% v/v) was sprayed on female ‘Pete 1’ and males ‘Chico’ and ‘Peters’ at different CPs in a location with CP>60 in Fresno County. Result of this study showed that the bud break and bloom responses of female ‘Kerman’ and male ‘Peters’ to Dormex® and oil spray differs at different chill portion applications. Both of the RBAs advanced bud break, with some applications successfully synchronizing bloom of male and female trees, and significantly increased the yield in all locations. However, early application of Dormex® at CP55 in location with CP≥65 caused a significant asynchrony between male and female trees, significantly increased the blank percentage and reduced the yield compared to non-treated control trees. In the low chill location, the significant higher yield was achieved by application of Dormex® at CP60, whereas, in location with marginal to good winter chill, bloom synchrony and yield were significantly higher by application of either Dormex® or oil at CP65 compared to non-treated control trees. Results also showed that bud swell to full bloom window for oil-sprayed female ‘Pete 1’ and male ‘Chico’ differ from male ‘Peters’ and oil spray at CP62 significantly improved bloom synchrony and increased the yield. The results showed that timely application of RBAs can be beneficial for successful bud break and bloom synchrony of female and male pistachios and can increase the yield in both marginal and low winter chill areas or years.
Khezri, M. (2024). A study on the efficacy of hydrogen cyanamide and winter oil applications on male and female pistachio bloom and yield. Acta Hortic. 1406, 257-266
DOI: 10.17660/ActaHortic.2024.1406.38
https://doi.org/10.17660/ActaHortic.2024.1406.38
endodormancy, winter chill, chill portion, bud break, flowering synchronization
English

Acta Horticulturae