Insecticides at different rates and combinations were used to produce different populations of cotton aphids infesting cotton in Oklahoma. The test was delayed until aphid densities neared 100 aphids/leaf. The E.P.A. established this threshold of 100 aphids/leaf to justify use of Furadan 4F to control mid-season cotton aphid infestation throughout the U.S. under the Section 18 Emergency Exemption Label. Efficacy varied greatly between treatments leading to a wide range of aphid densities which persisted up to 14 DAT. Variation in aphid densities and duration of the infestation after spraying allowed the impact of aphids on boll weight and yield to also be measured. High aphid densities had adverse effects on boll weight and yield, but not on lint grade or strength. There was no negative linear, or negative curvilinear relationship between aphid densities and boll weight or yield 1 DBT. However 3 DAT, 7 DAT, and 14 DAT a significantly negative curvilinear relationship with boll weight and a significantly negative linear relationship with yield occurred. Increased aphid levels reduced boll weight and yield. Significant yield loss occurred by waiting to spray until the E.P.A.'s established action threshold was reached. Action thresholds should be lowered to compensate for time needed to initiate treatment. Maintaining Oklahoma's current economic threshold of 50 aphids/leaf should allow ample time for reaction to initiate control keeping aphid levels below 100 aphids/leaf averting significantly yield loss in infested fields.