Can soil conditioners of plant origin be used for pest control?

Abstract

Bio-oil is a byproduct of the thermal decomposition of organic materials under low concentrations of oxygen at controlled temperatures. This product is commonly used as a potential soil conditioner. However, as it is of plant origin, this product may also have secondary metabolic properties capable of assisting in the alternative management of agricultural pests. Therefore, this work aimed to evaluate the acaricidal effect of bio-oil based on coffee straw and eucalyptus bark, obtained at a temperature of 600 ºC, on adults of the red mite Oligonychus ilicis. The treatments were calculated on a logarithmic scale, and the concentrations of the bio-oil solutions were 1.00; 1.58; 2.51; 3.98; 6.31, and 10.00 % (v v-1). Each solution was applied on mite adults, each treatment consisting of 7 Petri dishes, with 12 red mite individuals per dish. The experimental units consisted of coffee leaf disks (4 cm in diameter), with cotton moistened around these disks to prevent the mites from escaping. The application of bio-oil solutions on the mites was carried out directly, being sprayed with the aid of an Alfa 2 airbrush, connected to a calibrated compressor with a constant pressure of 1.3 psi. 2mL of solution of each concentration was applied. The experimental units were kept in a climate-controlled chamber (25 ºC, 70 % RH, 12h photophase). The acaricidal effect on adults was evaluated 24, 48, and 72 hours after spraying the solutions. Mortality data were submitted to Probit analysis (p≤0.05) using the R statistical program. Coffee bio-oil and eucalyptus bio-oil caused mortality in O. ilicis in a dose-dependent manner, with an estimated LC50 of 1.52 and 2.15 % (v v-1), respectively. The estimated LC90 of these bio-oils was 5.90 % and 8.02 % (v v-1), respectively, indicating that doses lower than the maximum concentrations used caused almost all the mortality of individuals under controlled environment conditions. Thus, it is concluded that the coffee straw bio-oil, as well as the eucalyptus bio-oil, have a high potential for use in the alternative management of adults of the red coffee mite O. ilicis.