Seasonal incidence of leaf mite, Oligonychus oryzae Hirst. (Acari: Tetranychidae) in Rice
S Chitra, R Vishnupriya, RP Soundararajan and K Ramaraju
Leaf mite, Oligonychus oryzae (Acari: Tetranychidae) is assuming the major pest status of rice and cause considerable yield loss in the rice cultivated under rainfed and upland systems. The seasonal incidence of rice leaf mite was studied in the rice fields of Tamil Nadu Agricultural University, Coimbatore on the popular variety CO-51 during 2015-16. The results revealed that the leaf mite incidence was more during September - October with the population ranging from 7.36 to 8.57 mites /1x10 cm leaf length. Minimum population was recorded during November 2015 to February 2016 (standard week 44 of 2015 to standard week 5 of 2016). Again the population gradually increased and reached its peak during the month of April with 16.49 mites /1x10 cm leaf length (standard week 17 of 2016). Correlation studies between the mite population and weather factors revealed that there was a significant positive correlation with maximum and minimum temperature, negative correlation with morning and evening relative humidity. Rainfall also showed negative correlation with mite population. Regression analysis revealed that for every unit increase in maximum and minimum temperature there was an increase of 1.15 and 1.36 mites, whereas for every unit increase in morning relative humidity, evening relative humidity and rainfall, mite population decreased by 0.72, 0.27 and 0.53, respectively.