ASSESSMENT OF YIELD LOSSES IN MUSTARD ( Brassica juncea L.) DUE TO MUSTARD APHID ( Lipaphis erysimi Kalt.) UNDER DIFFERENT THERMAL ENVIRONMENTS IN EASTERN CENTRAL INDIA

Abstract

Mustard aphid (Lipaphis erysimi. Kalt.) has been reported as one of the devastating pests in realizing the potential productivity of Indian mustard (Brassica juncea L.). The experiment was carried out to assess the yield losses in mustard due to mustard aphids grown in different thermal environments under protected and unprotected conditions. To provide different thermal environments the crop was sown on 5 dates i.e. 08, 18 and 28 November and 08 and 18 December during winter seasons of 1995- 96, 1996-97 and 1997-98. It was observed that yield attributes and yield of mustard was significantly decreased in delayed sowing even under protected conditions. On an average maximum seed yield of 1409 kg/ha was harvested when the crop was sown on 08 November under protected condition, while only 279 kg/ha seed yield was recorded under unprotected condition. Similarly the yield attributes and yields drastically reduced under unprotected condition as compared to protected one in all the thermal environments. On the mean basis 80.6, 81.4, 95.2 and 97.6 per cent yield loss was observed under unpro- tected condition as compared to protected condition in 08, 18, 28 November and 08 and 18 December sowing, respectively. It was also observed that the critical period of mustard exposure to aphids was found to be the 3 rd week after aphid appearance when the crop was in flowering stage and hence the con- trol measures have to be initiated before flowering. There was not much difference in natural aphid population/plant in the crop sown up to end of November while the aphid population increased sudden- ly in December sown crop.