Boron Fertilization of 'Sharwil' Avocados in Kona, Hawaii

Misshapen fruits of Persea americana Mill. cv. Sharwil were observed during the 1989-90 harvest season in Kona, Hawaii. To determine whether these fruit deformities were caused by boron (B) deficiency, B (0 and 23 g/tree), as solubor, and nitrogen (N) (90, 180, and 270 g/tree), as urea, were applied in a factorial combination to single tree plots on 8 cooperating farms. The first B application (February, 1990) significantly increased foliar B concentrations of the spring vegetative flush sampled in June, 1990; however, these B concentrations were still below the recommended level of 50 mg/kg. The second B application (June, 1990) significantly increased foliar B concentrations of the summer vegetative flush sampled in October, 1990, and these B concentrations were within the recommended B range. During the 1990-91 harvest season, B applications significantly increased the weights of deformed fruit. Perhaps, this increase in weights of deformed fruit on trees given B fertilizer was due to insufficient B levels in the tree after the first B application, during the critical period of flowering and early fruit development. Observations are being continued during the 1991-92 growing season.