Effect of synthetic pyrethroid insecticides on green leafhopper (GLH) and tungro (RTV)
1987
Valencia, S.L. | Mochida, O. (International Rice Research Inst., Los Banos, Laguna (Philippines))
Four synthetic pyrethroids - ethoproxyfen (0.1 kg ai/ha), cypermethrin (0.05 kg ai/ha), alphamethrin, and deltamethrin (0.0125 kg ai/ha) - were evaluated for Nephotettix virescens GLH and RTV control in the field in 1984 dry season (DS). Wet seedbeds of highly susceptible TN1 and susceptible IR22 were covered with nylon mesh immediately after sowing to protect seedlings from GLH. Starting 1 d after transplanting (DT), 8 insecticide applications were made at weekly intervals. Disease incidence was recorded at 60 DT. The same materials and methods were used in a 1985 wet season (WS) trial, but insecticide applications were reduced to five. In the 1984 DS, RTV infection in plots treated with any of the pyrethroids was significantly lower than in the untreated control. Cypermethrin gave the lowest RTV incidence. In the 1985 WS, RTV infection was significantly lower on IR22 treated with ethoproxyfen and cypermethrin and on TN1 treated with ethoproxyfen and deltamethrin. The degree of control with the synthetic pyrethroids improved with more frequent applications early in crop growth. On susceptible varieties, control of RTV by insecticides was low.
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