What Causes Warts on Certain Pumpkins?

For many, the arrival of autumn is marked by a visit to the pumpkin patch. Whether you're picking one for carving or cooking, you might come across pumpkins with warty surfaces. This isn’t a flaw—many varieties are intentionally cultivated to have this rugged texture.

While some pumpkins boast a smooth surface, others are prized for their bumpy, wart-like features. Agricultural experts deliberately breed these varieties to achieve their distinctive, rough appearance.

Certain warty pumpkin varieties are modern innovations. In 2008, Siegers Seed Company in Holland, Michigan, introduced a new type of pumpkin with green and orange warts after years of crossbreeding. Known as knuckleheads, these pumpkins' unique texture isn’t due to disease. Instead, it results from the fruit's high sugar content, which causes the skin to crack and form warts, as explained by Colorado Gardener.

In some cases, bumps and irregularities on pumpkins indicate health problems. Four mosaic viruses—papaya ringspot virus, zucchini yellow mosaic virus, cucumber mosaic virus, and watermelon mosaic virus—can affect pumpkins. The first two often cause significant deformities, including lumpy growths. These viruses are primarily spread by aphids, common pests for gardeners.

Edema can also cause warts on pumpkins. This condition arises when a plant absorbs more water through its roots than it can evaporate. The excess water increases turgor pressure, the force exerted by water against cell walls, leading to swelling of the pumpkin’s inner cells. This swelling damages and discolors the outer cells, resulting in grayish-brown blemishes.

Even when pumpkins develop lumps due to health issues, they are generally safe to eat. Carol Larvick, a food safety expert at the University of Nebraska, advised the Nebraska Extension in Dodge County that while mosaic viruses don’t cause premature rotting, severely deformed fruits may have a different texture, so personal judgment should be used.