BUT diseases are still around us. Over-watering, dust, low light, etc., can reduce the vitality of your plants.
Leaves often turn yellow and develop dead tips, and growth is weak and spindly.
Check the tubers for the black 'dirt that won't wash off'. This 'dirt' is actually a special structure called a sclerotium, formed by the fungus, which causes black scurf disease of potato, to allow it to withstand adverse environmental conditions. Also, look for potato scab which forms scabby, pitted areas on the tuber. If you cut open the tuber you may find a dry rot caused by another fungus, or a wet, stinky, soft rot caused by bacteria.