I have used aspirin in the garden as a fungicide to prevent blight, verticillium wilt, black spot, fusarium wilt, and septoria blight on nightshade crops. It has been a popular remedy for decades; my grandparents even used aspirin in the garden!
     
      Using aspirin is simple. Tomato plants have a natural defense mechanism; spraying tomato plants with aspirin will engage that mechanism and help create a healthier plant.
Mix 1 aspirin tablet with 1 1/2 gallons of water in a pump sprayer. Stir until completely dissolved. Then spray on the leaves both under and over the leaves.
It prevents blight, verticillium wilt, black spot, fusarium wilt, and septoria blight. It cures nothing. This should be applied as a preventive, not a cure, so spraying early, and often is the key.
It will not prevent fungus spores or mold, since they are external and deal with growing conditions.