Effects of agricultural spray adjuvants in surface tension reduction and spray retention on Eucalyptus leaves

Agricultural spray adjuvants (ASA) are widely used in pesticide applications to enhance the effective control of pest, weed and disease. The aim of this research was to investigate the effects of ASA used in Brazil agriculture on surface tension reducing capacity and foliar spray retention on different Eucalyptus species. Static surface tension of adjuvants at concentrations of 0.001, 0.0025, 0.005, 0.01, 0.025, 0.05, 0.1, 0.25, 0.5, 1.0 and 2.0% v v-1 were determined by the drop weight method. Spray retention on Eucalyptus leaves using ASA were performed at concentrations of 0; 0.005; 0.01; 0.05; 0.1; 0.5; 1.0 and 2.0% v v-1. The ASA assessed were: vegetal oil, mineral oil, spreader-sticker and a drift reducing based on soybean lecithin more propionic acid. All ASA adjuvants reduced surface tension of aqueous solutions. Heptomethyltrisiloxane (HT) provided the best performance on decrease of the surface tension reaching values below to 20 mN m-1 at concentration of 0.05% v v-1. Spray retention was influenced by Eucalyptus species, adjuvants types as well as adjuvants concentrations. The increase of ASA concentration contributed to reduce spray retention. Different characteristic of the adjuvants on spray retention was observed in different Eucalyptus leaves species. Eucalyptus grandis and Eucalyptus torelliana species showed respectively the lower and higher spray retention values. The mineral oil and vegetal oil provide the higher and HT the lower level of spray retention. Application at high spray volume must be carefully performed to avoid losses by run-off when added some ASA. Key words: Foliar retention, surfactant, application techniques, chemical control.