Black Spots on Grapevines
Discovering black spots on grapevines is a red flag that something is amiss. The spots are a symptom of an underlying fungal disease that has infected your grapevines. Since more than one disease results in black markings, take a more detailed look at those spots to determine whether your plants are experiencing the classic "black spot disease" most often associated with spots or another harmful disease known as "black rot."
Providing optimal care for your grapes is the most effective way of avoiding diseases such as those which result in the development of black spots. Care for your grapes by growing them in areas that offer full sunlight for best health. Though grapes thrive in nearly any type of soil, they perform best in moist, well-drained conditions. Avoid wet or waterlogged soil, which promotes the development of fungal disease. Additionally, extremely dry soil results in stressed plants, which are more susceptible to disease. Grapes grow best in U.S. Department of Agriculture hardiness zones 5 to 9.
Look for small brown-black to black spots on leaves and pay attention to their borders. If the spots grow, become gray and develop raised or red borders, your grapevines are infected with black spot disease, also known as anthracnose. Caused by the fungus Elsinoe ampelina, the disease also results in the formation of dark spots on stems and berries.
Black spots on grape vines may also be a symptom of a fungal infection commonly referred to as black rot. Caused by the fungus Guignardia bidwellii, this disease results in brown irregularly-shaped spots with dark borders. As the disease progresses, small black dots will appear within these spots. Black ovular spots develop on younger plant material such as new shoots. The tiny black spots are fungal growths; the larger black spots are areas of dying plant tissue which eventually sink, forming indentations.
Black spot infections result in stems which appear malformed and twisted, torn leaves and berries that shrivel until they look like "mummies," which remain attached to the vine.
With black rot infections, damage is similar and includes mummified berries. However, the berries drop prematurely from the vine. If the disease occurs before the fruit begins to grow, the fruit will fail to develop.
Particularly during periods of warm, humid weather, which most greatly promotes fungal diseases, entire plants may die.
Prevention is the best medicine for fungal diseases, which are easy to avoid when growers provide proper cultural care. Remove any weeds and debris to provide good air circulation around your grapevines. Contact a professional to create a fungicide program tailored to your particular plants, especially during wet seasons. Fungicides will not cure an existing problem but will aid both in preventing the development of diseases as well as controlling existing disease. For infected plants, remove and destroy affected plant material to prevent reinfection the following year.
- University of Illinois Integrated Pest Management: Black Rot of Grapes
- Ohio State University Extension: Grape Black Rot
- University of Kentucky College of Agriculture: Black Rot of Grapes
- Oklahoma Cooperative Extension Service: Growing Grapes in the Home Garden
- University of Illinois Extension HortAnswers: Grape Vitis Vinifera
- State Government Victoria Department of Primary Industries: Black Spot of Grapevines
Tarah Damask's writing career began in 2003 and includes experience as a fashion writer/editor for Neiman Marcus, short fiction publications in "North Texas Review," a self-published novel, band biographies, charter school curriculum and articles for various websites. Damask holds a Master of Arts in English and creative writing from the University of North Texas.