Powdery Mildew, Can You Avoid It?

— Written By ascheck and last updated by

The summer time here in Central North Carolina is an excellent time to grow and consume a variety of fresh local vegetables. Whether you grow them yourself or purchase them the freshness and taste is really hard to beat. Unfortunately for many gardeners this they will have many of their beloved vegetables fall pray to a fungus, which leads to an all too familiar disease known as powdery mildew. Powdery mildew can be encountered on many species of plants from roses to broccoli. However, powdery mildew is most often a problem for the various species of cucurbits that are commonly grown in this area.

The plant family Cucurbitaceae includes squash, melons, cucumbers, pumpkins, and gourds all of which have high susceptibility to the fungus that causes powdery mildew. That coupled with our hot, humid, and sometimes down right damp growing conditions has created a “perfect storm” type scenario for powdery mildew infestations. This growing season has been no exception as I have seen a large number of cases here locally in recent weeks.

A fungus known as Erysiphe cichoracearum causes powdery mildew on cucurbits. The initial symptoms of powdery mildew are small gray spots on the leaves and stems that can sometimes be mistaken for soil. The spots soon spread to fill a much larger portion of the plant before eventually killing off entire leaves. Affected leaves will eventually turn yellow and fall off, reducing yield and potentially causing your developing fruit to get sunburn. The infection can spread, killing off whole plants or even entire gardens. Once the disease gets started, especially on multiple plants it can be extremely hard to control.

Unfortunately for the unlucky gardener how finds powdery mildew in their garden there isn’t much that can be done. Fungicides can be applied, but generally they will only slow the spread of powdery mildew. Prevention is the key to avoiding powdery mildew outbreaks in your garden. The best thing you can do to prevent powdery mildew is to select resistant varieties when planting cucurbits. There are also other cultural practices one can follow that will help prevent powdery mildew such as proper spacing of plants, planting in direct sunlight, avoiding wetting the leaves, and by removing any dead leaves from around the plant. It is also a good idea to disinfect any tools between using them on different cucurbit species.

By using the right preventative tactics and by following the proper cultural practices in your garden powdery mildew can often times be avoided. It is also very important pay close attention to your garden and monitor for any signs of powdery mildew. If you see any leaves showing signs of powdery mildew remove of them immediately and dispose of them in a manner that will keep them from spreading to other susceptible species. Despite the susceptibility to this troublesome disease in many plants it is still entirely possible to grow fresh and healthy vegetables for you and your family, even cucurbits.

For more information on powdery mildew and how to prevent it, contact North Carolina Cooperative Extension, Lee County Center (919-775-5624).

Alec Check is doing a Horticulture Internship with North Carolina Cooperative Extension in Lee County this summer.