Make a thin paste of lemon juice and salt; spread the paste on mildew stains. Lay out the fabric in the sun to bleach it. Afterward, rinse and dry. Mildew stains on fabric can also be tackled with a paste of salt, vinegar, and water. If the stain is extensive, you can use up to full-strength vinegar.
Some garments may still retain a musty, mildewy smell even after washing. Get rid of the smell by soaking the garments in lemon juice and water and then letting them dry in the sun.