Phenyl Isocyanate-Modified Avermectin B1a Improves the Efficacy against Plant-Parasitic Nematode Diseases by Facilitating Its Soil Mobility

Root-knot nematodes are sedentary, soil-dwelling parasites that infect plant roots to disturb their nutrient and water utilization, causing significant yield losses. Avermectin is widely used in the field because of its excellent nematicidal activities; however, it is adsorbed by organic matter near the soil surface, resulting in poor migration in the soil, limiting its field performance. Many organic compound pesticides suffer from the same challenge. Six avermectin B1a (AVB1a) derivatives with phenyl carbamate groups were obtained and found to have increased water solubility and significantly decreased oil–water partition coefficients (Kow) and soil adsorption coefficients (Kf). Two soil mobility experiments verified that all derivatives could move to a farther location compared with AVB1a. These derivatives could reduce nematode viability, though the nematicidal activities were lower by nearly 1.5–5-fold compared with AVB1a. In the field, the six derivatives exhibited excellent efficacy, 20–30% higher than that of the control compound. This research emphasizes the significance of uniform distribution in the soil by hydrophilic modification with phenyl carbamate that increased the delivery efficiency and bioavailability of the agent, thereby improving its efficacy.