Four new cassava varieties (NR 8082, TMS 00033, TMS 91/ 453 and TMS 00447) were fertilized with NPK (20-10-10) at the rates of 0, 200, 400, and 800 kg/ha in an experiment with the crop planted early (April) in 1999 and then late (September) in 2000. Tuber yield was 28% higher in early-planted cassava than in the late cultivation. Yield was reduced by 44% in NR8082, 15% in TMS 00033 and 45% in TMS 00447 as a result of late planting. Tuber yield from NR 8082 (44t /ha) was the highest for early-planting while TMS 00033 gave the highest yield (31 t/ha) in late planting. Fertilizer influence on tuber yield was not significant in early-planted cassava. In late-planted cassava, significant reduction in yields was observed from the application of 400 and 800kg/hectare of fertilizer. Incidence of tuber rot was influenced by varietal differences rather than fertilizer rates. Incidence of rot was lowest in NR8082 (9-10%) and TMS 00033 (10-11%) in both plantings and the severity was mild in all the varieties. TMS 00033, a low cyanide variety, have tuber yields above 30 t/ha in both early and late plantings and is therefore recommended for adoption trials by farmers.

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Effect of mango mealybug and sooty mould attack on mango and the impact of the released Gyranusoidea tebygi Noyes on yield. Abstract-Introduction. The mango mealybug Rastrococcus invadens is a pest of horticultural crops, especially mango. Though this fact has been demonstrated and its parasitoid, Gyranusoidea tebygi, released for its control in many countries, quantitative information on the damage inflicted by the mealybug and post-release mango fruit production are still scanty. This study was therefore undertaken to investigate the damage caused by mango mealybug and its associated sooty mould on mango plants and to assess mango fruit production after the release of G. tebygi in 1989. Materials and methods. Laboratory experiments were set up to determine the effect of different populations of mango mealybug (0, 5, 10, 20, and 40 adults/cage) on the chemical constituents of mango leaves. The mould associated with the mango mealybug was identified and its effect on leaf temperature was studied. A mango orchard was studied for fruit production from the time of fruitlessness in 1990 to 1998 when fruit yield peaked. The resultant effect of the parasitism of mango mealybug by G. tebygi was monitored on the chemical composition of mango leaves during this period. Results. Protein, fat, carbohydrate, ash, crude fibre and moisture contents were depleted with increase in mealybug population. The isolated mould fungus Capnodium mangiferae was found to raise leaf temperature of infected mango seedlings. The population density of G. tebygi was found to be negatively but significantly correlated with mango mealybug population and positively correlated with mango fruit yield. Parasitism was highly correlated with mealybug population and yield, and was considered a major factor in the control of the pest and the subsequent increase in mango fruit yield. Rainfall did not have a significant impact on yield, mealybug population or sooty mould score. Discussion. The injury inflicted by R. invadens and its associated mould, and the enhancement of mango fruit production by the activities of G. tebygi on the mealybug were discussed. Nigeria / Mangifera indica / pest control / Rastrococcus invadens / Gyranusoidea tebygi / biological control organisms / yields Effet des attaques de la cochenille farineuse et de la fumagine sur manguiers et impact de la libération de Gyranusoidea tebygi Noyes sur leur rendement. Résumé-Introduction. Rastrococcus invadens, la cochenille farineuse du manguier, est un ravageur des productions horticoles, et du manguier en particulier. Bien que ce fait ait été démontré et que son parasitoïde, Gyranusoidea tebygi, ait été libéré dans de nombreux pays afin de contrôler le ravageur, des informations quantitatives sur les dommages qu'il inflige à la production en mangues sont encore minces. L'étude engagée a permis d'étudier les dommages provoqués sur manguiers par ce parasite et par la fumagine qui lui est associée et d'évaluer l'évolution des rendements après un lâcher de G. tebygi en 1989. Matériel et méth...

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