Urea Combined with 6-Benzyladenine Applied to the Foliage of Pistachio Trees during Nut-fill Reduced Floral Bud Abscission during the “On” Crop Year and Increased Yield the Following “Off” Crop Year

Abstract

Alternate bearing of pistachio (Pistacia vera L. cv. Kerman) is a significant problem in California. Excessive abscission of floral buds beginning in June and intensifying at the time of seed development (nut-fill) in July during the “on” year results in the next year's “off” crop. While the mechanism resulting in alternate bearing in pistachio has been identified, its physiological basis has not and there is no satisfactory horticultural practice to even out alternate bearing. Bud retention in pistachio was increased 3-fold and 2-fold for two successive years, respectively, on branches bearing greater than 70 nuts per cluster (an “on” crop) basal to the shoot bearing the buds for next year's crop with foliar applications of 0.25% N as low-biuret urea combined with 25 mg 6-benzyladenine per liter applied in early June and early July. In Sept. 1997, the crop produced by the buds treated in 1996, an “on” crop year, was harvested. The untreated control trees produced an “off” crop, 7.6 kg fruit per tree, yielding 0.5 tons split nuts (dry weight) per acre. Trees treated with 0.25% N as urea combined with 25 mg 6-benzyladenine per liter on June 1 and July 1 yielded 16.4 kg fruit per tree, resulting in 1.14 tons split nuts (dry weight) per acre (P ≤ 0.05).