Identifying and Treating Squash Diseases

Moldy yellow squash in the garden.

Growing squash plants is easy and fun. Squashes include both winter and summer types. Gourds are in the squash family as are pumpkins and zucchinis. Due to their soft and succulent natures, they are vulnerable to a range of squash diseases which require treatment. Aside from trouble with squash bugs, there are also a range of viruses, fungi and bacteria which cause wilting, rotting and malformation of the fruits. Some diseases may be treated, while others can only result in the death of the plant.

TIP: Our expert gardening advisor, Susan Patterson adds, "Squash is one of the oldest foods grown in America."

Squash End Rot

One of the most common diseases in squash is the squash end rot. This is a calcium deficiency disease which also causes blossom end rot in tomatoes. Too little calcium causes the plant problems in building fruit cells. As a result, the bottom of the fruit often does not get enough calcium. This problem often doesn’t appear until the fruit becomes larger. Then it becomes quite apparent as the cells begin to collapse, the rot begins and there is a black or dark brown indentation in the fruit which is often soft to the touch.

There is not a lot that can be done once this sets in. Prevention is better than cure, and the only real solution is to remove the rotting fruit and add a calcium rich supplement to the plant.

TIP: Susan suggests, "Sterilize pruning tools before and after use in hydrogen peroxide."

New fruit should begin to grow shortly and the plant should now have enough calcium to prevent squash rot from forming.


Squash diseases caused by viruses may make the plant dwarfed and mottled. Malformation of the fruit is a classic indicator and naturally this affects the flavor of any squash fruit provided. Aphids are commonly responsible for carrying this disease.

Viruses are usually untreatable. The disease spreads easily between squashes. To prevent contamination of other plants, it is often necessary to destroy the severely infected plants (by burning or trashing; squash plants with virus infections should never be composted), and try to keep aphid infestation to a minimum with sprays and by encouraging predators.

TIP: Susan emphasizes, "Always remove dead or diseased plants from the garden immediately."

Other Problems

Angular Leaf Spot is a bacterium which causes areas of rot on leaves. The solution is to remove any infected leaves and ensure that the plant is kept dry after watering.

Mosaic Virus deforms the plant, creating small leaves which have discoloration and spots of rot. This disease is caused by aphids, which spread the virus from plant to plant. Hence, along with treating the cucumber, a spray to control aphids is necessary.

Mildew, which is a fungus, creates white spots on the leaves and stems. This causes shedding of leaves. Infected plants have to be destroyed, but there are varieties which have been made resistant to the disease.

Verticillium Wilt is caused by another kind of fungus. This causes plants to wilt, and get a brown stain on the stems and roots. This fungus eventually kills the plant. It may linger in the soil where potatoes and members of the nightshade family are planted. The treatment is to have good crop rotation in future years.

TIP: Susan advises, "Stressed plants are prone to disease and insect infestation. Always keep your plants healthy by providing plenty of water (drip irrigation is best) and using organic soil."