Plant bioactive volatile products and their efficiency in aphid control

Abstract

The “farm-to-fork strategy” of the European Union aims to reduce dependency on pesticides and towards increased use of low-risk products, such as those based on botanical extracts. A product based on the mixture of the five natural compounds selected for their repellent or insecticidal properties, namely citral, (E)-anethole, farnesol, cis-jasmone and lemon essential oil, was evaluated against Myzus persicae Sulzer (Hemiptera: Aphididae). Three formulations were prepared using various surfactants at different ratios: the first one with Tween80, the second one with soy (Glycine max (l.) Merr.) lecithin and the third one with soy lecithin and sunflower oil (Helianthus annuus L.). The oil-in-water nanoemulsions at 1% were tested in a laboratory study with Petri dishes using a computer-controlled spraying apparatus (equivalent application of 200 l/ha). The mean efficacy was 45%, 71% and 63%, respectively, with a least statistically significant difference (LSD) at 5% comparing the first two formulations. A field experiment (in two pepper, Capsicum anuum L., greenhouses) at Torreblanca Exp. Stat. in Murcia (Spain) followed in April 2020 in which a reduction in aphid populations only occurred by spraying the product formulated with soy lecithin. Phytotoxicity was also observed but was lower in the formulation that contained sunflower oil. Nanoemulsions were characterised using a Zetasizer, and a polydispersion of 2–3 populations of particles, ranging from 15 to 341 nm in size, was found with the Tween80 formulation and bigger sizes (250–438 nm) with the soy lecithin and sunflower oil formulation, which were more stable (Z potential = −28.15 mV). The application of ultrasounds reduces the Z-average to 100 nm in the mixture product with stability for at least 14 days. Another field experiment was repeated in February and April 2021. The plants were sprayed sequentially with the following: a) mixture product at 0.5% formulated with soy lecithin and sunflower oil, b) 3% cottonseed (Gopsyppium hirsutum L.) oil in 3% soap water (Feb.) or 1.5% cottonseed oil in 1.5% soap water (Apr.) and c) cis-jasmone at 0.25% formulated with Tween80. The treatment with the mixture of bioactive volatiles (a) was not more effective than that of the fixed seed oil (b). In February, the instantaneous population growth rate (ri) of aphid populations showed a significant reduction when the plants were sprayed with cottonseed oil. Further research is recommended for the formulation and application methods of the products being developed