Cotton hardlock which is believed to be caused by Fusarium verticillioides severely reduce lint yield in the southeast. Because the pathogen is transmitted by thrips, we hypothesized that control of thrips though spray applications could reduce hardlock. We started studies on cotton hardlock in FL in 2002. In 2004 and 2005 we conducted more studies to further test if Fusarium F. verticillioides is the causal agent for hardlock and to evaluate the efficacy of fungicides on reducing hardlock. The fungicides used included Topsin (Thiophanate-methyl), Folicular(Tebuconazole), and Headline (Pyraclostrobin) Hardlock incidences were up to 3-fold greater for cotton bolls inoculated with F. verticillioides compared to the controls, proving that Fusarium is the causal agent for the disease. Higher fungicide application rates and frequency of application increased leaf area index and reduced leaf diseases. Bolls per plant and lint yield were not affected by fungicide application. There was a positive correlation between the number of fungicide application and yield (r = 0.454 and p < 0.0174). We will continue the studies into 2005.