EFFECT OF SOWING DATES ON INCIDENCE AND ABUNDANCE OF INSECT PESTS AND NATURAL ENEMIES IN SOYBEAN [Glycine max (L.) Merrill]

Abstract

The effect of different sowing dates on incidence and abundance of insect pests and associated natural enemy population was studied by taking three staggered sowings at 15 days interval (2nd fortnight of June, 1st and 2nd fortnight of July). The data obtained from the three staggered sowings, revealed that the occurrence of insect pests and natural enemies was similar in all the staggered sowings except for their level of incidence. Peak period of infestation of tobacco caterpillar occurred only once in June 2nd fortnight sowing compared to July 1st and 2nd fortnight sowing, wherein two peaks were recorded. In case of green semilooper only one peak each was recorded in June and July 2nd fortnight sowings whereas two peaks were observed in July 1st fortnight sowing. In case of stem fly, one peak was observed in June 2nd fortnight sowing compared to July 1st and 2nd fortnight sowing wherein two peaks were recorded. Infestation of stem girdler recorded two peaks in all the three staggered sowings.The highest incidence of major insect pests was recorded in the 2nd staggered sowing with a yield of 11.50 qha-1. However, 3rd staggered sowing recorded comparatively low population but with lowest yield of 9.00 qha-1 due to the heavy rains in the initial period which adversely affected the crop growth and development. The normal sowing (2nd fortnight of June/1st staggered sowing) recorded low insect pest population compared to that of both the sowings with highest yield (13.50 qha-1).