Sustainable management of two-spotted spider mite Tetranychus urticae(Acari: Tetranychidae) on clementine citrus groves

Abstract: Tetranychus urticae is a major pest of Clementine citrus (Citrus reticulata Blanco)on Spanish groves. This mite infests fruits and leaves, feeding on them. The profuse webbingon leaves hinders both the performance of biological control agents and chemical control. As aresult of their attack, leaves acquire characteristic chlorotic spots and often drop from the treeprematurely. Besides yield reduction, even light infestations on fruits can result in scarring,thus decreasing quality and the commercial value of fruits. The number of authorisedpesticides used in agriculture has been reduced, mainly acaricides, thus it is necessary toprovide alternatives to chemical control for T. urticae on citrus. In this study, on a commercialcitrus Clementine grove located at Vinaroz (Castellón), the population dynamics of T. urticaepopulations was followed from June to November. On a block randomized design, controlstrategies based on mineral oil sprays and Neoseiulus californicus releases were evaluated,compared to an acaricide treatment and to untreated control plots. At the end of August amineral oil spray was applied to the entire thesis. Two mineral oil sprays significantly reducedthe number of symptomatic leaves respect to the control during seven weeks, and alsosignificantly diminished T. urticae population densities during two months. Nevertheless, at theend of August, both symptomatic leaves and T. urticae population densities raised, achievingcontrol levels. Releases of N. californicus did not lead to a reduction of the numbers ofsymptomatic leaves, but reduced T. urticae population densities compared to the control.Persistence of phytoseiid releases was brief, probably due to the high temperatures occurredduring summer. At harvest, the proportion of attacked fruits and the magnitude of symptomswere evaluated. For the entire thesis, the proportion of fruits with attack symptom was low andsimilar, except for the acaricide thesis, where was lower. Values ranged from 4% to 12% offruits with low blemish, accepted by market quality standards, and from 2 to 4% with moreprofuse scars, but always inferior to 12% of the overall fruit rind. An approach to improvecontrol strategies based on mineral oils sprays, N. californicus releases or both methodscombined is required in order to provide a more sustainable two-spotted spider mite pestmanagement in citrus.