EFFECT OF MULTIPLE PEST INJURIES ON RICE YIELDS

Transcription

1 Indian J. Agric. Res., 40 (4) : , 2006 EFFECT OF MULTIPLE PEST INJURIES ON RICE YIELDS Gururaj Katti, I.C. Pasalu, P.R.M. Rao*, K. Krishnaiah and N.R.G. Verma Directorate of Rice Research, Hyderabad (A.P), India ABSTRACT Field experiments were carried out during kharif (wet season) and rabi (dry season) seasons of 1998 and 1999 to study the impact of multiple pest injuries on rice yields. Observations were recorded on injuries due to different pests on 200 randomly selected hills over an area of 1ha at weekly intervals starting from 15 DAT throughout the crop growth and hill-wise yield was recorded at harvest. Regression analysis of the data based on extent of injuries due to major pests revealed that there was significant reduction in yield due to per cent white ears by the stem borer while silver shoots produced due to gall midge infestation did not have significant effect. Though, the injuries due to rice tungro disease and rats were observed in limited number of hills, they also had adverse impact on rice yields. INTRODUCTION Every year a large proportion of rice yield is lost due to pests like insects, diseases and weeds and analysis of the yield losses has become a diverse research domain (Teng, 1987). Crop loss data are useful in decision making at all pest management levels and in fact often form integral part of pest management programmes. Puri (2000) reported that yellow stem borer, gall midge and brown planthopper were the key pests in rice causing 10 to 70%, 15-60% and 25-30% loss, respectively. In the past, many pest control decisions have been mainly based on pest density-yield loss relationship. However, other research studies have revealed that total herbivore density does not reflect the actual impact on final rice yield. Instead, regular monitoring of herbivore injuries throughout the season may give a better estimate of the impact on yield (Johnson, 1990). Keeping this in view, field experiments were carried out as a part of Directorate of Rice Research (DRR) - International Rice Research Institute (IRRI) collaborative Rice IPM Network activity at three locations viz., Farmers. field, Medchal, Ranga Reddy dist., A.P., DRR Research farm, Hyderabad and Research farm, Agricultural Research Station (ARS), Maruteru during kharif (wet season) and rabi (dry season) seasons of 1998 and MATERIAL AND METHODS Two hundred hills were selected at random across an area of 1 ha in a field planted with rice. The hills were then marked with bamboo pegs and observations were recorded starting from 15 DAT at weekly intervals, on injuries due to different pests on the same 200 hills through harvest. At harvest, hill wise yield was recorded for the 200 hills and corrected for 14% moisture content. Observations were also recorded on filled and unfilled grains as well as whiteheads separated from normal panicles. Care was taken to ensure that no plant protection chemicals were applied in the experimental field. Data were also recorded on the agronomic practices including inputs given in the experimental field. The data was subjected to suitable statistical analysis to draw valid conclusions. RESULTS AND DISCUSSION The results revealed that at Medchal and Hyderabad, in the early vegetative stage, the crop received injuries mainly from yellow stem borer, and foliage feeders like rice whorl maggot, hispa, leaf folder etc. but during the maximum tillering stage, the injuries were mostly from the major pests, gall midge and stem borer, which continued till reproductive stage. After that white ears due to yellow stem * Agricultural Research Station, Maruteru, ANGRAU, West Godavari dist., A.P., India.

2 Vol. 40, No. 4, No. of hills No. of injuries/dat Fig. 1. Frequency distribution of injuries, Medchal, kharif 1999 Frequency Days after transplanting No. of injuries Fig. 2. Frequency distribution of injuries, Hyderabad, kharif 1999 Fig. 3. Effect of insect pest injury on rice yield, farmers field, Medchal, kharif 1999

3 3 0 0 INDIAN JOURNAL OF AGRICULTURAL RESEARCH Fig. 4. Effect of insect pest injury on rice yield, Hyderabad, kharif 1999 Frequency Days after transplanting No. of injuries Fig. 5. Frequency distribution of injuries, ARS Maruteru, rabi 2000 Fig. 6. Effect of insect pest injury on rice yield, ARS Maruteru, rabi 2000

4 borer and neck blast disease were mainly observed till harvest. Rice tungro virus (RTV) disease was observed (only during kharif, 1999) to an extent of 17.5% at 75 DAT at DRR research farm, which increased to 62.5% at 85 DAT and it persisted upto harvest. The data on frequency distribution of injuries showed that in the early stages of crop growth the number of injuries per hill due to insect pests ranged from one to three (Fig. 1 and 2). The frequency of hills with one injury consistently increased till 60 DAT, while hills with two injuries were observed mainly during the period between 40 and 60 DAT. Thereafter, there was a significant increase in hills without injuries till harvest. The results revealed that only the major pests, stem borer and gall midge persisted throughout the crop growth ( DAT) as indicated by the hills with only one or two injuries during the season. A regression analysis of the data based on percent dead hearts and white ears due to stem borer and percent silver shoots due to gall midge (Figs. 3 and 4) throughout the season (i. Medchal - kharif 1999: Y= WE**-0.06 SS and ii. Hyderabad - kharif 1999: Y= WE**-0.09 SS) revealed significant reduction in yield due to per cent white ears while gall midge infestation showed no significant impact. At Maruteru, initially, in the vegetative stage, the crop was infested by rice whorl maggot, leaf folder and hispa was also observed but their incidence did not exceed 10%. At 45 DAT, 19% of the hills (38 hills) were completely damaged by rats during kharif The incidence of other important pests viz., Vol. 40, No. 4, planthoppers, stem borer and sheath blight disease was also low. However, at harvest, stem borer and sheath blight infestation were observed along with damage due to birds. Regression analysis of the data based white ears due to stem borer and sheath blight did not indicate any clear trend during Mar/f 2000 due to insufficient number of affected hills. However, the severe impact due to rat damage on yield was clearly discernible as the affected hills were completely destroyed at 45 DAT. During rabi 2000, the frequency distribution of injuries showed that the number of injuries per hill due to insect pests ranged from one to three (Fig. 5). There was significant reduction in yield (Y= WE**-0.04 SS) due to per cent white ears while gall midge infestation showed no significant impact (Fig. 6). This was in confirmation with the results obtained in the farmers field at Medchal as well as at DRR research Farm, Hyderabad. Earlier, Savary et al. (2000) using principal component regression model estimated that sheath blight, leaf blast and brown spot among the diseases and white ear injuries due to stem borer caused important losses in rice. The present study confirmed the significant impact of white ears due to stem borer on rice yield. It was also evident that injuries due to tungro disease and rat damage could adversely affect rice yields in certain situations. It is concluded that a better understanding of the complex combination of yield reducing factors including the impact of multiple pest injuries on yield is vital in accurate estimation of crop losses by pests. REFERENCES Johnson, K.B. (l990). In: Crop Loss Assessment in Rice, IRRI, Los Banos, Philippines, pp Puri, S.N. (2000). In: Farmer-Led Integrated Pest Management fn India and the Pacific. Asian Productivity Organization, Tokyo, pp Savary, S. et al. (2000). Plant Disease, 84: Teng, P.S. (1987). Crop Loss Assessment and Pest Management. American Phytopathological Society, St. Paul, MN.

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