Brown Spots on Thompson Seedless Grape Leaves

Winter Damage

• Himrod grapevines, a cultivar of Thompson seedless grapes, are very susceptible to winter or early spring frost and freezing damage that leaves brown patches on the leaves of the grapevine. Cold weather causes the flesh of the leaves to freeze, leading to brown dead spots on the leaves that weaken the overall health of the plant. Severely damaged leaves will not recover and should be removed from the grapevine to prevent them from becoming hosts to disease.

Fungal Leaf Spot Diseases

• Thompson seedless grapevines are susceptible to various fungi that cause leaf spot diseases. Brown, slightly raised spots with a variety of other colorations, such as a yellow halo, black center or reddish brown colors are indicative of fungal diseases. These diseases are rarely serious, although if a large number of leaves are affected, a fungicide spray is essential to repairing the damage to the leaves. Prune damaged grape leaves, make sure the soil is well-drained and apply fungicides regularly to prevent fungal leaf spot diseases.

Black Rot

• Black rot is a common disease of Thompson seedless grape leaves and other types of table grapes, according to Ohio State University. Despite its name, black rot causes the formation of light brown spots on the leaves of Thompson grapevines initially; over time the spots darken and sometimes create elongated spots on the stems of leaves. Control this fungal disease with proper cultural care of the grapevine, including regular pruning and fertilization, well-drained soil and evenly spaced vines that are not overcrowded. A preventative fungicide spray regimen helps gardeners avoid black rot.

Pest Problems

• Aphids, spider mites and Japanese beetles are only a few of the pests to which table grapevines, including Thompson seedless grapes, are susceptible. As these pests feed on the leaves of the grapevine, they leave small dead patches behind them, which turn brown over time. Pest control practices, including proper spacing of grapevines and a regular schedule of pesticide sprays, are essential to avoiding the damage to the growth and health of the grapevine caused by pests.