Hardlock in cotton can be caused by environmental factors such as high humidity and cloudy days at boll opening. Some fungi, such as Fusarium verticillioides have been associated with hardlock. In Florida applications of Topsin M during flowering have sometimes resulted in reductions in hardlock and substantial yield increases. In this 2 year study the affects of Topsin M applications on hardlock and subsequent yields were studied. Topsin M was applied in 4 regimes at each of two locations in South Carolina in 2004 and 2005. At each location applications were made to Deltapine 555 BR and Paymaster 1218 BR cotton. Data on plant growth and development and especially leaf health and retention were collected. Treatment regimes at the Edisto location consisted of: 1) Non-sprayed check; 2) Weekly sprays beginning with first true leaf until end of flowering; 3) Weekly sprays during flowering; 4) Spray every other week for three times during flowering; 5) Weekly sprays beginning with the first true leaf until the beginning of flowering. At the Pee Dee R.E.C. regime 5 was omitted. Sprays consisted of 0.5 lbs/acre Topsin M 70% WP.