Aphids and citrus responses to nitrogen fertilization

The aim of this study was to assess the effect of nitrogen mineral fertilizer on the vegetative growth of citrus as well as on the densities and population dynamics of the main aphid species Aphis spiraecola Patch (Hemiptera, Aphididae). Two trials were conducted on clementine trees, Citrus clementina Hort. ex Tan., in 2016 and 2017 in Tunisia. The quantities of nitrogen delivered varied from the control to the triple recommended dose of nitrogen (3ARD) in a complete randomized block design. Results showed that all vegetative growth parameters evaluated for the clementine trees responded positively to the amount of nitrogen supplied. The highest values were obtained with the highest Nitrogen doses in both years. A positive response also was observed for aphids for all doses, with densities increasing proportionally to Nitrogen inputs. The highest dose (3ARD) increased aphid populations by 3 times compared to the control. The aphid population dynamics differed between the two years, probably under the influence of other factors such as rainfall. Thus, too much nitrogen should be avoided in citrus orchards. The control of aphids with the aim to reduce insecticide sprays cannot be separated from the management of nitrogen fertilization.