Lesser mealybug and Alternaria black core rot through a smaller navel in ?Navel? oranges

?Navel? sweet orange [Citrus sinensis (L.) Osbeck] fruit are characterized by the presence of a secondary fruitlet (navel) located inside the stylar-end of the primary fruit. Fruit with large navel-end openings have increased susceptibility to develop navel-end fruit splitting and navel-end rot. Furthermore, large navel-end openings can provide refuge for insect pests including mealybugs. Foliar application of the plant growth regulator and synthetic auxin, 2,4-dichlorophenoxy acetic acid (2,4-D) during flowering time reduces the size of the navel, as well as that of the navel-end opening. The objective of this study was to determine if the closing of the navel-end opening by foliar application of 2,4-D could reduce the susceptibility of ?Navel? sweet orange fruit to mealybug [Planococcus citri (Risso)] infestation, Alternaria [Alternaria alternata (Fr.) Keissl] infection and the subsequent development of Alternaria black core rot (ABCR). Foliar application of 2,4-D at full bloom (FB) increased the percentage of fruit with fully closed navel-ends significantly. These results concur with previous research and were consistent across different production areas, cultivars and seasons, irrespective of the concentration and formulation of 2,4-D used. Apart from two anomalies, all 2,4-D treatments at FB resulted in a lower percentage of mealybug infested fruit at time of harvest and significantly reduced the percentage of fruit infected with ABCR. A combination treatment of 10?mg?L?1 2,4-D and 0.20?mL?L?1 tebuconazole applied at FB was most successful in reducing ABCR infection and therefore provides a novel control method for black core rot in ?Navel? sweet orange fruit. SourcesOckert P.J. Stander, M.J. Gilbert, S.D. Moore, W. Kirkman, Gerhardus C. Schutte, Benefits of reducing the size of the navel-end opening in ?Navel? sweet oranges (Citrus sinensis), Crop Protection, Volume 96, June 2017, Pages 123-129, ISSN 0261-2194, http://dx.doi.org/10.1016/j.cropro.2017.02.009.(http://www.sciencedirect.com/science/article/pii/S0261219417300352) Picture by citricas.com