Tomato leaf mould is a common fungus that attacks tomatoes grown in humid places. The mold attaches itself to the leaf and feeds off of the humidity to grow and thrive. It is vital to take care of the situation immediately so that the foliage isn’t dramatically infected. Infected leaves will decrease the amount of tomatoes yielded. With this type of fungus, it is rare that the fruit is infected as well. The signs to look for are all on the leaves. The tops will begin to develop small, white, gray, yellow, or pale green patches. The underside of the leave will have a fuzzy feel that is purple in color. Sometimes the fuzz will be olive green. The “fuzz” is actually spores of the fungus. The infected tissue becomes yellowish-brown and the leaf begins to wither, eventually falling off of the plant. Ultimately the whole plant will wither and die.