Management of maize stem borer Chilo partellus swinhoe (Lepidoptera: Pyralidae) using selected plant powders with insecticidal properties

Stem borer (Chilo partellus) is one of the serious pests of maize in Sri Lanka. At present, this pest is managed through foliar application of liquid or granular formulations of recommended insecticides. The use of insecticides can be environmentally disruptive and can result in reducing beneficial insects and accumulation of residues in the harvested produce. In order to develop safer control methods, field studies were conducted during Maha 2014/15 and Yala 2015 to evaluate the efficacy of crude powders of locally available plants against maize stem borer. Experiments were laid out in a randomized complete block design with four replicates. The treatments tested were leaf powder of Ocimum spp., Lantana camara, Tagetes spp. and seed powder of Azadirachta indica. These treatments were compared with the recommended Diazinon 5G and an untreated control. The variety MI maize hybrid 1 was used. Plant powders and Diazinon were applied twice as whorl applications at 3 and 5 weeks after planting at a rate of 15 kg/ha (except neem at 5 kg/ha). During Maha 2014/15, at 8 weeks after planting, the percentage damaged plants in the plots treated with plant powders ranged from 17 to 27 % while the damaged plants in the untreated plot was 40 %. During Yala 2015, at 8 weeks after planting, all the plants treated with plant powders except those treated with Tagetes spp. showed significantly lower percentage of damage (21-23 %) compared to untreated control (36 %). Diazinon 5G was superior in reducing stem borer damage during both seasons. Larval population and severity of stem borer damage were also significantly lower in Ocimum spp., L. camara, A. indica and Diazinon treated plots compared to the untreated control during both seasons. Results also showed that application of crude powders of these three plants increased the maize grain yields by 43-45 % and 24-27 % compared to the untreated control during Maha 2014/15 and Yala 2015, respectively.