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Effect of Larval Density of Helicoverpa armigera (Hubner) on Pod Damage and Yield of Chickpea
First Online 07-01-2022|
Methods: To determination of per cent pod damage and yield of chickpea due to different larval density of H. armigera is an important tool to reduce the cost of cultivation by avoiding the unnecessary use of pesticides. Therefore, a pot experiment was conducted in arranged in a completed randomized design with four replications. The pots were placed under natural field conditions and take observation at Research farm, Rajasthan Agricultural Research Institute, Durgapura, Jaipur during 2015-16 and 2016-17.
Result: The results revealed that least per cent pod damage (29.05, 24.78%) was recorded when the larval population was one per plant, while the maximum pod damage (64.55 and 67.76%) was recorded during 2015-16 and 2016-17, respectively. The simple liner correlation analysis indicated that there was a significant positive correlation (r= 0.989 and 0.999) between the larval density and per cent pod damage. Further, a significant correlation was noticed between larval density and number of healthy pods per plant, reduction in yield, yield per plant, total number of pod and damaged pods were -0.964, -0.976; 0.98, 0.986; -0.98, -0.986; 0.117, 0.126 and; 0.985 and 0.992, respectively during 2015-16 and 2016-17.
MATERIALS AND METHODS
Laboratory culture of H. armigera was maintained as described earlier (Anonymous 1995). Sequential batches were maintained in the culture to get freshly emerged larvae coinciding with the post flowering stage of the potted plants.
Preparation of potted plants
Cement pot of 30 cm diameter and 30cm height were used. They were filled with compost soil mixture (1:1), lightly irrigated and allowed to settle for two days before sowing. Sowing was done on the third week of October at the rate 3-4 seeds per pot. Altogether 25 pots were prepared and they were thinned to maintain a single plant per pot after establishment. The plants were given irrigation, hoeing and other cultural practices as per requirement.
Individual round cages of 0.5 cm width and 1.5 m height were prepared with while net on bamboo pegs fixed at soil level to protect them from natural infestation. Uniform 24 cages were selected and arranged in a completed randomized design with four replications. The pots were placed under natural field conditions.
Application of treatment and observation
To the individual healthy plants in the cage, emerged larvaeof H. armigera were released on 24 caged plants at post flowering stage at evening hours when the plants were about 100 days old and larval population density of 0, 1, 2, 3, 4 and 5 per plant was maintained. The pots were cage and each treatment was replicated four times. Before releasing, all plants were thoroughly examined to make these free from any pests.
The dead larvae if any were replaced by the larvae of the same age group from the laboratory culture. On completion of the larval period the cages were removed. At harvest, healthy and damaged pods were recorded. The grain yield was also recorded. The data thus obtained were subjected to statistical analysis.
Determination of EIL
The EIL was determined by the procedure suggested by Hammond and Pedigo (1982):
Management cost was calculated based on prevailing market price of the insecticides and application cost, while the market value of grain was calculated from the whole sale value of gram at the local market around the harvesting time.
Estimation of economic threshold level
The method reported by Johnston and Bishop (1987) to estimate the economic threshold was adopted in the present investigation. They established that economic threshold level would be the population at EIL minus the increase in pest population per day. Thus in the present investigation, the increasing rate of larval population in the field was determined by recording the weekly population of H. armigera during larval activity. The rate of increase in population was calculated arithmetically.
ETL was estimated by deducting the increase in larval population per day from the respective ETLs.
RESULTS AND DISCUSSION
The finding of present investigation is in agreement with the earlier work carried out by Odak and Thakar (1975) who reported that when four larvae of H. armigera per square meter in chickpea at flowering stage and pod formation stage caused economic damage. Sharma (1985) in a study reported the economic injury level of 1.0 larvae/m row length under artificial condition, while 2.0 larvae/m row length under natural conditions. Reddy et al., (2001) also support these finding and concluded that on an average a single larva per plant reduced the yield to the extent of 138.5 kg/ha and the EIL for H. armigera were determinate as 8 and 6 larvae/10 plants during the two years, respectively.
- Anonymous (1995). Technology for production of natural enemies. ICAR Publication pp. 75-78.
- Anonymous (2016). ICAR-AICRP Chickpea Report. Project Coordinator’s Report 2016-17. Annual Group Meet on Chickpea, August 28-30: 2017 pp. 36.
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