Studies on the sowing date of cotton in the Sudan Gezira: II. The relationship between sowing date of cotton and the incidence of insect pests

Abstract

In factorial experiments covering a range of sowing dates and insecticide treatments the numbers of fleabeetle, jassid and whitefly on cotton in the Sudan Gezira were shown to be strongly influenced by the date of sowing and the age of the crop.Attack by fleabeetle was most severe on cotton seedlings from July and early August sowings. Few fleabeetle were found on either more mature plants from these sowing dates or on seedlings from later sown cotton.Whitefly numbers were highest on late July and early August sown cotton. Peak numbers were attained attained in late September and October and then fell to very low levels in November irrespective of date of sowing.Jassid numbers were related both to plant age and to time of year, more being found on cotton sown, in July and early August early in the season and on later sown cotton later in the season. The highest numbers were found in November and December at which time populations were higher on cotton sown in mid-August or later than on earlier sown cotton.