Grape Diseases and Insects

Below are a few of the common grape issues seen here in Connecticut; however, there are many more as well

There is a wonderful pocket guide from Michigan State University full of color photos to help you identify grape issues that include diseases, insects, animals, nutritional deficiencies, and chemical iinjury,

Initially I thought I would record all disease for all cultivars. However, there are so many issues that can arise and this has proved to be too time consuming. Instead I will evaluate them primarily on whether or not they produce a good crop of grapes - after all that is the bottom line.

Notice the typical ‘bird’s eye’ infection on the grapes. Leaves may curl and distort like a clenched fist. Lesions appear on stems.

Anthracnose is caused by a fungus. The disease is of European origin; therefore, Anthracnose is generally worse on American grapes. Sanitation is extremely important. Remove old, infected plant material, which is the primary source of spores for new infections.

Organic growers can be selective about which cultivars to plant and apply Organically approved lime-sulfur sprays during the dormant season – this fungicide helps to reduce the amount of primary inoculum. Subsequent fungicide sprays every 10 to 14 days from bud break to veraison (color change of grapes) may be necessary where Anthracnose is severe. Caution, some cultivars are sensitive to sulfur – see widely available charts.

If you want to avoid sprays, choose cultivars that are resistant to Anthracnose.

Notice the round orange-brown circles on the leaves and the damage to the grapes. Also notice the typical black ‘mummy’ grape in the lower foreground of the right photo. To the left of it is a grape in the earlier stages of becoming a ‘mummy’. Some cultivars are more susceptible to Black Rot than others.

Organically approved fungicides (copper and sulfur) are not very effective for Black rot control. So, the most efficient way to control Black Rot is the use of good cultural practices. Avoid susceptible cultivars. Also, sanitation is a key component to controlling Black Rot. Clear all mummies from the ground after leaf drop or till them into the soil prior to bud break. Remove all mummies from the vines during dormant pruning.

Grape Phylloxera is a microscopic aphid-like louse that lives on and eats sap in grape leaves and roots. The foliar form overwinters as eggs on canes. Eggs hatch when the leaves have emerged in the spring. Nymphs move to upper leaf surfaces and begin feeding. Their feeding induces the formation of galls on the leaves. After about 15 days, the adult stage is reached within the galls. 6-7 generations occur on the leaves. Crawlers will move from older leaves to more tender leaves at shoot tips.

There are no good controls for Grape Phylloxera other than avoiding susceptible cultivars and using Phylloxera-resistant rootstock grafts for susceptible cultivars.

Japanese Beetles can do extensive damage to grape leaves. Fortunately, Milky Spore bacteria effectively controls them, is approved for Organic use, and is safe to use. Follow the directions on the bag to inoculate your soil. One application lasts for years and eliminates the bulk of them by killing the grubs overwintering in the ground. The grubs are large – larger than the adult beetle itself. Adult Japanese Beetle stragglers that survive can be collected by dropped them in a mason jar half-full of wine. They are easy to scoop from the leaves to the jar.