Spatial evaluation of the pesticide application method by farmers in a paddy field in the northern part of Vietnam

The pesticide application method is important for controlling a target pest effectively. The current status of pesticide application techniques for small-scale rice farmers in Red River Delta, Vietnam aims to be clarified to control serious rice pest insects, such as Nilaparvata lugens (Stal) ( Hemiptera: Delphacidae), which live on the bottom of rice plants. Interviews with farmers revealed their preferences and practices towards pesticide application. The farmers' application technique was evaluated by investigating the droplet deposition level at different heights of rice plants (bottom, middle, and top) and the distance from the spray walking path (near, middle, and far) in a rice paddy field using water-sensitive paper (WSP). Droplet deposition on WSPs was categorized into eight ranks. Ordered logistic model analysis revealed that the droplet did not reach to the bottom of plant, while no significant differences were found among the distances from the walking path. The droplet deposition rank and the mortality of N. lugens were positively correlated. The low efficiency of the pesticide applied by farmers to control N. lugens could be one of the factors that contribute to the insecticide-resistance development of N. lugens in Vietnam.