Cabbage flea beetle, phyllotreta spp (coleoptera: chrysomelidae) distribution, damage and management on ethiopian mustard, brassica carinata a. Braun, in arsi zone, oromia

Abstract

Ethiopian mustard (Brassica carinata A. Braun) is an important plant to many small-scale farmers in Ethiopia as a vegetable, a source of income, to grease ‘injera’ and bread baking clay pan and oil. Its production, however, is constrained by several factors like very low in yield, its unacceptable level of naturally high levels of erucic acid and glucosinolates in its seed, lack of improved crop management, diseases and insect pests like flea beetle, diamondback moth etc. The objective of this study was to determine the distribution, damage and status of flea beetles, and their management using different seed rates and screening the chemicals with effective rate during 2011 cropping season. Survey of flea beetle was done in Lemu Bilbilo, Tiyo and Hetosa Woredas of Arsi Zone by taking purposive samples of mustard fields within a distance of about 5 km from each other. From each farm five one m2 plots were used for sampling and the three first growth stages primordial, first true leaf and second true leaf stages were considered. Significant difference was found (P<0.05) among some farms in the mean number of flea beetles and the damage they cause at these considered stages. Variation was also recorded in mean number of productive plant stalks and plant population reduction. Monitoring of flea beetle damage, the effect of varying seed rate and screening effective insecticides were done in Kulumsa Agricultural research center by sowing Yellow Dodolla mustard. Two rows of 1m length were used for sampling flea beetles and their damage for the seed rate and screening and four rows of 1m length rows were used in monitoring. The number of flea beetles and the damage they sustained were higher during first true leaf and second true leaf stages and found decreasing from vegetative stage to matured stage. The six seed rates revealed no significant difference in mean number of flea beetles but the mean number of damaged plants was found to be decreased from plots sown with the lower seed rate to the higher seed rates for the all the stages. Productive plants and plant population reduction were maximum for plots of the highest seed rate (10.8g) and minimum for plots of the lowest (2.7g) seed rate. Maximum mean of yield (1917.8kg/ha) was obtained from plots sown with seed rate of 5.4g (10kg/ha). The higher rate of Carbaryl, Malathion and the two rates of Fenitrothion were found with reduced mean number of flea beetles and the damage (P<0.05) they caused to the plant. Productive plants and yield (kg/ha) were higher for plots treated with higher rate of Carbaryl, Malathion and lower rate of Fenitrothion. Significant positive correlation was found among flea beetles, their damage to the plant and plant population reduction. The correlation was significant and negative for yield (kg/ha) vs number of flea beetles, yield vs number of plant damage and number of plant damage vs productive plants. This study generally revealed that the recommended rate of seed rate and Fenitrothion at its recommended rate can be used in cabbage flea beetle management and the monitoring of the beetles should involve the seed pod setting stage.