Comparison of Three Methods for Establishing Economic Threhold Levels for Jacobiasca iybica (De Berg.) on Eggplant

No Thumbnail Available
Date
2015-06-23
Authors
Binyason, Sampson Akoi
Journal Title
Journal ISSN
Volume Title
Publisher
UOFK
Abstract
Three studies were conducted at Kenana Reasearch station – Abu Naama, Sennar State. Three methods for establishing economic threshold level for Jacobiasca iybica (de Berg) on eggplant were compared in cage, field controlled and farmer participatory experiments. The objectives of the experiments were (a) to establish the jassid density- damage relationship (b) to identify the most critical crop growth stage where there is a maximum injury or loss and (c) to determine the lowest populations of the cotton jassid at which the farmers should spray their eggplant crop to maximize their profits. The relationship between pest density and damage of eggplant demonstrated that with an increase in jassid numbers in the cage, field controlled experiments and in farmer participatory experiments, there was a corresponding increase in yield reduction, accelerated by duration of the infestation. The critical stage for eggplant growth is the seedling stage at the age between 30-45 days after sowing (DAS). The action threshold (economic threshold) for jassid on eggplant should not exceed 0.5 jassid / leaf in cage experiments or 50 jassids /100 leaves when eggplant are at seedling stage (30-45 DAS) and should not also exceed 100-150 jassids/100 leaves in the field when eggplants are at vegetative stage (60-65 DAS). Eggplant at flowering stage (90-95 DAS) is tolerant to 200-300 jassid levels and loss in yield is minimal. Farmers AT or ET can be derived empirically if proper sampling techniques are employed but this requires constant monitoring and adjustment. The variation in eggplant yield among farmers reflect differences in decision making experiences to control the jassid populations. However, despite such differences in decision making, the present results demonstrated that farmers' mean ETL does not exceed 100 jassids/100 leaves which is comparable with the results obtained from the field controlled experiments. Eggplant yield varies from season to season in accordance with the varying jassid populations; such populations require separate determination of intra-seasonal AT to guarantee profitable yields. The proposed AT for summer, autumn and winter in the field should be between 50-100 jassids/100 leaves. The observed leaf colour changes in the cage studies caused by different jassid densities compared to the control 'O' may be used to establish AT which may perhaps be the simplest method for farmers to adopt to replace the conventional counting method used by research scientists. The field controlled experiment method is the recommended method for establishing AT for jassid on eggplant. This method is simple and represents the actual natural field situation in which the plants and insect interact freely. It can be used in small and large scale experiments thus make it advantageous over the cage and empirical observations at farmers' field method. However, more efforts should be exerted to train farmers to be able to recognize and differentiate colour changes due to jassid damage, confirmed by its presence on the crop since there may be other factors associated with similar symptoms in the open field. Three studies were conducted at Kenana Reasearch station – Abu Naama, Sennar State. Three methods for establishing economic threshold level for Jacobiasca iybica (de Berg) on eggplant were compared in cage, field controlled and farmer participatory experiments. The objectives of the experiments were (a) to establish the jassid density- damage relationship (b) to identify the most critical crop growth stage where there is a maximum injury or loss and (c) to determine the lowest populations of the cotton jassid at which the farmers should spray their eggplant crop to maximize their profits. The relationship between pest density and damage of eggplant demonstrated that with an increase in jassid numbers in the cage, field controlled experiments and in farmer participatory experiments, there was a corresponding increase in yield reduction, accelerated by duration of the infestation. The critical stage for eggplant growth is the seedling stage at the age between 30-45 days after sowing (DAS). The action threshold (economic threshold) for jassid on eggplant should not exceed 0.5 jassid / leaf in cage experiments or 50 jassids /100 leaves when eggplant are at seedling stage (30-45 DAS) and should not also exceed 100-150 jassids/100 leaves in the field when eggplants are at vegetative stage (60-65 DAS). Eggplant at flowering stage (90-95 DAS) is tolerant to 200-300 jassid levels and loss in yield is minimal. Farmers AT or ET can be derived empirically if proper sampling techniques are employed but this requires constant monitoring and adjustment. The variation in eggplant yield among farmers reflect differences in decision making experiences to control the jassid populations. However, despite such differences in decision making, the present results demonstrated that farmers' mean ETL does not exceed 100 jassids/100 leaves which is comparable with the results obtained from the field controlled experiments. Eggplant yield varies from season to season in accordance with the varying jassid populations; such populations require separate determination of intra-seasonal AT to guarantee profitable yields. The proposed AT for summer, autumn and winter in the field should be between 50-100 jassids/100 leaves. The observed leaf colour changes in the cage studies caused by different jassid densities compared to the control 'O' may be used to establish AT which may perhaps be the simplest method for farmers to adopt to replace the conventional counting method used by research scientists. The field controlled experiment method is the recommended method for establishing AT for jassid on eggplant. This method is simple and represents the actual natural field situation in which the plants and insect interact freely. It can be used in small and large scale experiments thus make it advantageous over the cage and empirical observations at farmers' field method. However, more efforts should be exerted to train farmers to be able to recognize and differentiate colour changes due to jassid damage, confirmed by its presence on the crop since there may be other factors associated with similar symptoms in the open field.
Description
Keywords
Citation
University of khartoum
Collections