Document Type : Research Article
Authors
1
Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran
2
Associate Professor, Department of Plant Protection, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Ahvaz, Iran
3
Iranian Research Institute of Plant Protection
4
Department of Plant Production and Genetics, Faculty of Agriculture, Shahid Chamran University of Ahvaz, Iran
10.22067/jpp.2026.96271.1261
Abstract
Introduction
Rapeseed, Brassica napus (Canola) is one of the most important oilseed crops in the Brassicaceae family having significant economic value. The global production of Canola is expected to increase due to global oil use and renewable energy directives being established. Damage by insect pests is resulting in an annual yield loss in oilseed rape production of 15% on a European scale. Management of insect pests in rapeseed rely heavily on pesticides due to the lack of effective crop rotation and resistant cultivar. The mealy cabbage aphid, Brevicoryne brassicae L., is one of the important and key pests of canola, which using chemical insecticides is the main control method. Imidacloprid (IRAC 4A), the most well-known and widely used representative of the neonicotinoid insecticides, is recommended to control this aphid in Iran. It provides systemic protection in plants. The outer surface of canola leaves, with their waxy layer, are susceptible to drops of solution washing off during spraying. Agricultural adjuvants are tank-mix additives that can solve such problems and increase the efficacy of insecticides by improving the physical and chemical properties of the insecticide’s solution. There has been very limited research on the role of adjuvants in improving insecticide performance in rapeseed. This research, aimed to evaluate the effects of three commercial adjuvants (Rapido®، Spredex® and Eco-Tac®) on the efficiency of imidacloprid (SC35%) to control the mealy cabbage aphid in canola crop. These adjuvants have different properties, such as wetting, sticking and spreading. Imidacloprid is formulated as suspension concentrate type (SC) which is water-based formulations. It is known that in SC formulation, the solid particles dispersed in a liquid carrier, and it is hard to spread on the Canola leaves. Therefore, this kind of formulation needs more adjuvant for better performance.
Materials and Methods
The project was performed in a research farm in Firouzabad city (Fars province, Iran), based on a completely randomized design with 8 treatments and 3 replicates. The efficacy in the sampling units were recorded at 1, 7 and 14 days after treatment, using the Henderson and Tilton's formula. The surface tension and the contact angle of the spray solution were also measured using an automatic interface tensiometer. Determination of the residual effects of insecticides is very important helping the choice of spraying frequency to avoid unnecessary insecticide applications. The treatments were: imidacloprid (recommended dose); imidacloprid+ Rapido®; imidacloprid+ Spredex®; imidacloprid+ Eco-Tac®; 20% reduction of imidacloprid dosage + each adjuvant. The control treatment was sprayed by water only. An atomizer sprayer was calibrated before running the experiment. The sprayer was cleaned well with water before applying each treatment. The application rate of the Rapido and Eco-Tac adjuvant was 0.1% in spray solutions, while in the case of Spredex was 0.05%. The results of the field efficacy trials were subjected to an analysis of variance (ANOVA), and the mean values of the treatments were then separated using a Tukey test with the SAS software (version 9.1). The threshold to assess significant differences was set as α = 0.05.
Results and Discussion
The results showed that all adjuvants were able to improve the efficacy of imidacloprid. For example, after 3 days after treatment, the imidacloprid alone, showed 78.81% efficacy (b statistical group), however the efficacy in “imidacloprid+ Rapido®”, “imidacloprid+ Spredex®” and “imidacloprid+ Eco-Tac® “ was evaluated as 90.93, 89.26 and 87.99%, respectively (a statistical group). The results of the surface tension and the contact angle measurements indicated that when adjuvants were added to the imidacloprid solutions, the contact angle decreased substantially as a result of the lowered surface tension of the droplets. When Rapido® and Spredex® were used in combination of reduced dosage of imidacloprid (20%), the efficacy of imidacloprid stayed as high in all days after treatment, being 88.94 and 92.43% in 3 days after treatment. In the case of Eco-Tac®, when used with 20% reduction of imidacloprid, the efficacy was 77.86% (statistical group b), which was not significantly different from imidacloprid treatment alone. Our results also support this statement as the adjuvant improved the efficacy of imidacloprid insecticides with the SC formulation. Furthermore, our results indicate that the selection of appropriate adjuvants (such as Spredex® and Rapido®) can allow for reduction use of imidacloprid up to 20% without reducing efficacy, which is important from an economic perspective, reducing environmental pollution, and resistance pest management.
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