WhenVerticillium dahliaeKleb. was grown under a negative pressure potential of −0.039 MPa, conidial production increased 800% over that of untreated control fungus. The increased production occurred when the fungus was grown on Czapek Dox broth, on sugar-maple sap, or on sugar-maple sap amended with asparagine. Fungal survival within a host is discussed in light of the data.