In six years of field studies, early-season releases of the native moth Bactra verutana Zeller were evaluated as a biological control for purple nutsedge (Cyperus rotundus L.). Establishment from adult releases required at least 10 pairs of moths per release; establishment from larval release could be achieved with a single release of two or five newly-emerged larvae per shoot. When shoots averaged 4 or 7.5 cm high at the time of such releases, aboveground growth was reduced 32 to 62% after 30 days. Three to eight weekly releases of larvae reduced the topgrowth of nutsedge planted in rows of cotton (Gossypium hirsutum L. ‘Stoneville 213’) 30 to 68% 6 to 8 weeks after the last release. Weekly releases of about five larvae per shoot repeated three, four, or five times in 1976 and 1977 reduced nutsedge growth so that seed cotton yield equalled that of cotton in plots without nutsedge. MSMA (monosodium methanearsonate) applied at the rate of 2.2 kg/ha 5 and 7 weeks after cotton emergence gave greater control of purple nutsedge topgrowth and a yield of seed cotton equal to that resulting from three to five larval releases of about five larvae per shoot beginning when purple nutsedge averaged 7.5 cm high. When MSMA was applied at 7.5 and 8.5 weeks after cotton emergence, the addition of two early-season releases of larvae were also necessary to achieve nutsedge control and seed cotton yield equal to that produced by three to five releases of larvae.