Huanglongbing (HLB) is a disease greatly affecting citrus production in Florida. The disease, caused by a phloem limited bacterium, results in phloem plugging, which disrupts carbohydrate translocation from leaves to roots and contributes to tree decline, increased fruit drop and eventually tree death. Foliar fertilization has been used by growers as a management strategy to improve tree health and maintain productivity of HLB-infected trees. While excessive potassium (K) levels in citrus tissue can result in fruit with thick peels, lower juice acidity, and cause poor color development, foliar application of K at post-bloom can significantly increase grapefruit size without negative side-effects. However, there is scant information available about effects of micronutrients on citrus fruit quality.
The goal of this experiment was to evaluate the effect of foliar nutrition, applied throughout the growing season, on grapefruit quality at harvest and the development of decay and peel breakdown during subsequent storage. The study was conducted in two commercial red grapefruit groves near Fort Pierce, Fl. Foliar fertilizer sprays were applied four times in 2014 and three times in 2015. Peel color, peel puncture resistance, juice percentage, Brix, and titratable acidity (TA) were evaluated for two consecutive seasons. Additionally, peel thickness was measured from one grove for the second season but was not affected by foliar fertilization. For both years, peel color, juice percentage, Brix, and acidity were not affected by foliar fertilization in either grove for both seasons. The only exception was in one grove during the second season where the application of fertilizer containing micronutrients, K and P, or DKP alone, resulted in significantly greater chroma (color intensity) than the control. For the first season, no significant differences were observed in percentage decay or peel disorders of fruit stored either at room temperature for up to six weeks, or after 8 weeks at 10 °C and two weeks at room temperature. Fruit from the second year is still undergoing evaluation. Overall, supplemental foliar fertilization did not significantly affect fruit quality of these two red grapefruit cultivars for the first two years of the study.