Influence of season and weather factors on the occurrence of the sorghum stem borerChilo partellus(Swinhoe) in Tamil Nadu

Abstract

Abstract Stem borer attack varied significantly on sorghum sown during different fortnights, ranging from 4.7 to 24.0% and 9.5 to 37.4% at 30 and 45 days after sowing (d.a.s.) respectively. The crop sown during the first fortnight of March was highest, followed by that sown in the second fortnight of February, in terms of stem borer damaged plants, damage rating, percentage dead hearts and percentage stem tunnelling. The least damage was in the crops shown during the second fortnight of June and of October. There was an indication that for every 1°C reduction in minimum temperature, there was a decrease of 1.69% stem borer damage at 30 d.a.s. At 45 d.a.s. none of the weather elements significantly contributed to the damage. During the summer the duration of egg to adult period of C. partellus on sorghum was significantly shorter at 39.48 days than in winter when it was 56.5 days. Double the rate of fecundity and higher fertility rate was also observed in summer.