Control Methods for the Small Brown Planthopper at the Rice Heading Stage

The small brown planthopper (Laodelphax striatellus) not only transmits viruses that cause rice viral diseases such as rice stripe virus disease, but also congregates on the panicles to cause damage during the heading stage of late rice. To clarify the control efficacy of pymetrozine and other pesticides against the small brown planthopper at the heading stage of late rice and the application techniques, Cheng Qinhai and others from the Plant Protection Station of Haining City, Zhejiang Province, conducted field trials.

The experiment set up a total of 6 treatments: 40% chlorpyrifos emulsifiable concentrate at 100 mL per mu, 10% nitenpyram aqueous solution at 30 mL, 10% imidaclothiz wettable powder at 30 g, 25% pymetrozine wettable powder at 20 g, 25% buprofezin wettable powder at 75 g, and a clear water control. When the rice was at the grain-filling stage, spraying was carried out with a manual sprayer at a water volume of 50 kg per mu. At the time of application, the generation overlap of the small brown planthopper was relatively obvious, with low-instar nymphs accounting for 58.3%.

The test results showed that chlorpyrifos and pymetrozine had ideal control efficacy against the small brown planthopper on the panicles; the former had good quick-acting performance, while the latter had better persistence; nitenpyram ranked next in control efficacy, while imidaclothiz and buprofezin had poor control efficacy against the small brown planthopper on the panicles. A single application of pymetrozine could effectively control the damage of the small brown planthopper at the heading stage, while chlorpyrifos required one additional application.

According to monitoring, the high temperatures in July-August had an inhibitory effect on the small brown planthopper, and after the weather turned cool in September, its reproduction accelerated. The suitable period for controlling the small brown planthopper at the heading stage is about 7 days after heading (mid-to-late September). It is suggested that in production, pymetrozine can be used alternately with chlorpyrifos, dichlorvos, and others to delay the development of pesticide resistance; in years when the small brown planthopper breaks out heavily, chlorpyrifos or dichlorvos can be mixed with pymetrozine to enhance quick-acting performance and persistence. For controlling the small brown planthopper at the heading stage of late rice with 25% pymetrozine wettable powder, apply 20 g per mu mixed with 50 kg of water for spraying.