Insect Resistance in Cotton in Sudan

Abstract

In Sudan, cotton is the most important cash crop. About 80 percent of it is irrigated and grown in the Gezira and neighbouring areas. Here, the cotton whitefly, boll-worms (mainly Heliothis), jassid and aphid are serious pests. The whitefly, since mid 1950s, and Heliothis, since mid 1960s, have attained notoriety. Hetiothis damages flower buds, flowers and bolls and reduces yield. The white-fly debilitates plants and reduces both yield and quality. Further, whitefly and aphid excrete copious amounts of sugary fluid excreta (honeydew) which makes the cotton sticky and difficult to gin and spin. The sticky cotton has poorer fibre length, strength, maturity ratio, micronaire value, fibre weight per cm, yarn strength and appearance (Khalifa, unpub.). In 1968, a special Committee on Cotton Stickiness recommended two additional sprays for insect control at the end of the season to reduce stickiness (Abdel Rahman & Eveleens, 1979). Since then, pesticide use has increased greatly. However, whitefly and stickiness problems have continued unabated, and the average cotton yield dropped to an all-time low in 198O-81 despite an expenditure of about 65 million dollars on chemical control of cotton pests during the said season.