Moderate to slightly light occurrence of the second generation of rice stem borers in Suijiang County in 2007

Rice stem borers in our county include the yellow stem borer (Scirpophaga incertulas), the striped stem borer (Chilo suppressalis), and the giant stem borer (Sesamia inferens). In the riverside area, 3 generations occur per year; in the mid-mountain area, 2 generations occur per year. At present, the first generation in the riverside area has ended, and the second generation is beginning to occur successively.

According to observations at our station's Fengchi pest and disease monitoring point, this year's second-generation moth flight began on June 10, 1 day earlier than last year and 2 days later than normal years, with the peak day on June 18, 1 day later than last year and 8 days earlier than the historical average; by June 25, a cumulative total of 234 moths had been trapped, with the yellow stem borer, striped stem borer, and giant stem borer accounting for 94.9%, 4.7%, and 0.4% respectively. The moth count for this generation is 27.9% of the historical average of 838 moths and 82.1% of last year's 285 moths. The moth dynamics at the Zhongcun monitoring point are also similar to those at the Fengchi point. Regarding field egg mass, on June 17, 59 paddy fields were surveyed around the Fengchi monitoring point, with an estimated egg mass per mu of 21 to 163, averaging 74.2; fields with more than 30 egg masses per mu accounted for 67.4%, and fields with more than 80 egg masses per mu accounted for 10.2%, with early-transplanted fields having more than late-transplanted fields. Judging from the combined effects of moth count, weather, and other factors, this year's second-generation rice stem borers are a moderate to slightly light occurrence; the peak hatching period of stem borer larvae will be in late June, and the peak damage period will be in early to mid-July.

Although this year's second-generation rice stem borer count is lower than the historical average and last year, this year's rice transplanting period was long and the area of late transplanting was large; at present, some rice seedlings have already jointed while others are still tillering, which favors larval infestation, and the damage from the same amount of insect source is greater than in normal years. To control stem borer damage, it is advisable to spray insecticides such as shachongshuang, shachongdan, diduoming, and mingqingqing during the peak larval hatching period to before the second instar, that is, from late June to mid-July, to control stem borers and also control planthoppers. If pesticide application is delayed until deadheart seedlings are already visible, the damage already caused cannot be reversed, and since the larvae are older and more resistant to pesticides, the control effect will be poor, making the effort half as effective.