Fungi tend to attack wood when temperatures range between 50 and 90°F (10–32°C). Wood needs to be moist for fungi to grow: The most serious decay occurs when the moisture content of the wood is approximately 30 percent; wood with a moisture content of less than 20 percent will usually not decay, and any infection will not progress. Wood that is too wet will not decay because the excess moisture does not allow fungi sufficient access to air, thus impeding their growth.