Communication between adult male and female Diparopsis castanea Hmps. was disrupted by ultra-low-volume spraying of cotton in a 0·2-ha field cage and in an open-field plot in Malawi with a polyurea-based microencapsulated formulation of the mating inhibitor 80% (E)- and 20% (Z)-9-dodecenyl acetate (IIA). When sprays containing 38·7 or 105·3 g IIA/ha were applied at 6-day intervals within the cage, reductions in mating of 62–66% and in oviposition of 72–78% resulted. Larval infestation was reduced by an average of 61% over a 52-day period. Effective release rates during these experiments were 4–19 mg/IIA/ha. Spraying at 6-day intervals with 15·9 g IIA/ha, however, had no significant effect on mating, and applications of 25·8 g of IIA/ha at 12–14 day intervals in the presence of high moth populations produced a reduction in female mating of only 19% despite a release rate of 4·4–53·0 mg/ha/h. Physical and chemical evaluations of microcapsule deposition on cotton plants indicated a low application efficiency, with an ‘effective’ spray deposition on plants of only 3·25–20·05% between pre-flowering and maturity. In an open-field spraying trial, applications of 38·7 g IIA/ha at 14–15 day intervals reduced oviposition by 75% from expected levels. Application of 15·7 g IIA/ha, however, had no disruptive effect in the field. Gas-liquid chromatographic analysis revealed no chemical interaction or marked effect on the release rate of IIA when carbaryl and IIA were sprayed in combination. Indirect evidence indicated that the microencapsulated formulations used possessed a considerable ability to withstand rain when applied to plants.