Mold and wet rot have many similarities. They both consist of fungal spores linked together by hyphae (stems), they both require moisture, they both contain a musty odor and they can both have the potential to damage the surfaces on which they settle. As a result of these similarities, you may encounter one of these fungi and wonder whether you have mold or wet rot. To best discern between the two, you should familiarize yourself with the differences.
Wet rot grows specifically on wood and plant surfaces. Mold can grow on wood surfaces, but it can also grow on foods, plaster, soil, grout, tiles and carpeting. If you find fungus growing on a non-wood surface, you most likely have mold, though in rare cases, the problem may also point to yeast or rust. If you have fungus growing on a wood surface, you must consider other attributes to determine whether you have a mold or wet rot issue.
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If you have a fungus growing on wood, notice the consistency. Mold has a velvety, sometimes slimy appearance. The color can vary dramatically -- depending on the type of spore -- from extremely light to black, but wet rot by contrast typically appears in patches of white and dark brown. Additionally, wet rot bears a much fuzzier appearance than mold and can also appear thicker in its consistency. Wet rot can cause fruit -- such as the fruit on trees -- to rot within 24 hours. Mold primarily affects the wood.
Besides the obvious physical differences, wet rot and mold refer to completely different fungi. Wet rot refers primarily to a specific fungus called Coniophora puteana. Mold, on the other hand, is a generic term that refers to thousands of different fungi like Stachybotrys (black mold), Cladosporium, Biploaris and Aspergillus, some of which release toxins into the atmosphere. A mold is simply any multicellular fungus (containing a hyphae) that can grow freely on foods and household surfaces. Since wet rot cannot grow so freely, it does not constitute a mold, even though it contains all of the other characteristics of mold.
If you have a white, fuzzy fungal growth on a plant or tree, it might still constitute an entirely different fungus than the one that causes mold or wet rot. Powdery mildew and downy mildew also affect plants but do not constitute mold in the traditional sense, as they only affect plant life. Powdery mildew and downy mildew will appear softer than wet rot, more chalky than fuzzy, and grow more prominently on the leaves than the wood.