How can I remove mildew stains from a white cotton shirt?

Treat the mildew with hydrogen peroxide and soap. Let sit until the stains lift and wash as you normally do.

Please double check what the shirt is made of. If it's 100% cotton you should be able to soak it in a mild soap and water. Gently rub the stain with a soft toothbrush And launder as usual. Double check that the stain is removed before tossing it in a dryer. If it isn't an expensive shirt, and dependig on the severity of the mildew, it may be best to replace it.

f you use Chlorine bleach with your whites, then do so and the mold should disappear.

I like using vinegar- check out some great advice: http://www.hometalk.com/diy/clean/fabric/q-how-do-i-get-mold-out-of-clothing-14015342

Bleach

Soak in bio wash powder overnight and the wash on Hot.