Squash may rot on the vine if the squash blossom isn't pollinated or as a result of blossom end rot. Some squash may rot as a result of a bacterial or fungal infection.
Proper watering and fertilization of squash plants can reduce some types of rot. For instance, over watering may leave squash plants susceptible to fungal infections. Anthracnose, a fungus, is identified by brown spots on fruit before the fruit falls off the vine.
The National Gardening Association recommends growing squash on a trellis, using drip watering and using mulch to prevent fungal and bacterial infections caused by over watering. North Dakota State University recommends using a natural mulch, such as wood shavings or straw, to maintain soil moisture and prevent over watering.
Failure to fertilize is a problem that typically occurs early in the season, before male flowers are present on the vine. Unfertilized squash are identified by small, unripe squash that have a wilted appearance before falling off the vine. Manually fertilizing squash plants may solve this issue. Additionally, squash plants may produce fruit later in the season after male flowers have developed.
Blossom end rot is characterized by small squash that rot near the bloom. Blossom end rot typically resolves with proper watering and cultivation methods. Cultivate plants only after the root system is well established. Avoid over cultivating plants to encourage growth and prevent blossom end rot.