Summer squash and zucchini fruits can decay from a disease called wet rot, caused by the fungus Choanephora cucurbitarum. The fungus infects wilted blossoms and spreads to attached fruit. Infected fruit decays rapidly, and the mold on the rotted area resembles clusters of black-headed pins. Often, secondary bacterial rot also occurs, which turns the fruit into a mushy mess.
The fungus is spread by insects, wind, and splashing water. Disease development is promoted by high-moisture conditions. There have been no practical control methods developed.
