Application of insecticides on cotton in Zambia: Timing of spray applications

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Abstract
The timing of insecticide spray application was evaluated to improve the management of cotton pests. The results showed that early spraying for Heliothis management on cotton in Zambia may not be entirely needed in all seasons and in all cotton growing areas of Zambia. The Heliothis infestation generally increased during the tenth week after germination coinciding with the flowering of cotton so the farmers in most cases could avoid the first or second spray starting at seventh or ninth week after the germination of cotton as currently recommended for routine sprays. In field trials, the economic threshold for Heliothis a key pest of cotton in Zambia was found to be 0.50 eggs per plant, when three to four sprays gave similar yields to five routine sprays. In all trials, the routine five sprays never provided significantly higher yields than scouting‐based treatments. The optimum cotton yields were obtained by applying 30 g a.i./ha with an ‘Electrodyn’ sprayer as compared with 57 ga.i./ha of the same insecticide recommended for conventional spraying in Zambia.