Malathion applied aerially and by ground at rates of 8, 12, and 16 oz. ultra-low-volume (ULV) per acre was effective against boll weevils for at least 48 hours after application unless rainfall occurred. Effectiveness of the three rates was similar with the 8 oz. rate being slightly less effective than the 12 or 16 oz. rates. Mortality over the three rates was compared by three methods: weevils were released into the field before application and recovered later; weevils were placed in mesh bags on treated cotton plants; and weevils were placed in petri dishes with treated cotton leaves. Reducing the rate of malathion from 16 to 12 oz. per acre for boll weevil eradication is indicated. Rates as low as 8 oz. per acre for fields on the leading edge of the eradication program should be tested over a county-wide area. In addition to the substantial cost savings, lower rates of malathion may be less detrimental to beneficial insects. Rainfall of as little as 0.05" reduced the effectiveness of all treatments significantly and reapplication after rains should be considered.