The disruption of Brassicaceous tissue has been shown to have pesticidal activity due to their production of glucosinolates. The hydrolysis of these glucosinolates when exposed to air and the release of many volatile compounds of which the most important antimicrobial agent is isothiocyanate, is a process called biofumigation. Biofumigation with brassica cover crops has not been well studied in tobacco. The purpose of our experiments was to evaluate the effect of biofumigation on populations of Phytophthora nicotianae in the soil and on disease progression throughout the growing season. A pilot field study was conducted during the summer of 2008. Incorporation of a mustard cover crop ( Brassica juncea 'Pacific Gold') was compared to plots with no cover crop (bare ground) to examine the effect on populations of P. nicotianae in the soil. Results showed that plots with the incorporated mustard had lower (P=0.05) populations of P. nicotianae than plots with bare ground. However, no effect was seen on incidence of disease in the Burley tobacco varieties KT-206 and KT-204. Based on these results a greenhouse study and another field project was performed in 2009 to look at the effect of incorporated mustard and wheat cover crops, as well as no incorporated plant biomass, on survival of chlamydospores of P. nicotianae . Our greenhouse study showed that incorporated 'Pacific Gold' mustard significantly lowered populations of P. nicotianae in soil (P=0.05) as compared to incorporation of wheat. Although not significant, incorporated wheat lowered the survival of chlamydospores in soil. The field study in 2009 showed no significant differences between mustard vs. wheat cover crop incorporation when looking at populations of P. nicotianae in the soil, incidence of black shank, disease severity on roots or yield.