The Effect of the Main Environmental Factors, the Rotational Crops and the Pesticide Applications on the Populations of the Major Cotton Pests in the Gezira Scheme

Abstract

Helicoverpa armigera (Hub), Jacobiasca lybica (de Berge), Bemisia tabaci (Genn.) and Aphis gossypii (Glover) were the major cotton insect pests in the Gezira Scheme. Those insect pests were affected by various factors and independent variables most important of which are the weather conditions, the other crops and the pesticides used in the area. Detailed data concerning these factors have been compiled in this work during the period of 1970 to 2003 and were subjected to statistical analysis. The results of this study are intended hopefully to be utilized in forecasting the seasonal severity of these pests. The following are the important significant correlations: A positive and highly significant correlation is recorded between the African Bollworm (ABW) H. armigera and the maximum temperature during the period August – October, mean average temperature during September – January and mean relative humidity (RH) during Sept. – Jan. A positive and highly significant correlation of Jassid was detected between jassid numbers and mean maximum temperature during September–January and mean average temperature of July- February. Moreover, a negative but significant correlation was shown between jassid numbers and the number of insecticide sprays per iv season, the cotton post-sowing rainfall and the total rainfall of the season. Lastly, a significantly positive correlation was detected when jassid numbers were correlated with the areas under groundnut of the same season. White fly (B. tabaci) numbers showed a positive and highly significant correlation with the annual areas grown with cotton, number of sprays/season, both mean average temperature and RH during Aug – Oct., cotton pre-sowing rains, post-sowing rains and total annual rains. Only two significant relationships between aphid (A. gossypii) and the independent variables were recorded. The first one is the positive and highly significant correlation with the annual areas under vegetables. The other one is the positive and significant correlation with the mean minimum temperature during the period Aug – Oct.