Grape Diseases and Pests

Question 1

Pierce’s Disease

Answer 1

The Xylella fastidiosa is spread by the blue-green sharpshooter in California and by sap-feeding insects in Europe. Insects feed on a plant and transmit the bacteria inside the plant, where it travels through the xylem vessels and spreads the infection. Infected vines appear stressed, with leaves turning red or yellow in the summer, berries shriveling, and dead and dried leaves falling off the vine.

Question 2

Phylloxera

Answer 2

Microscopic insects that suck sap and feed on the leaves and roots of grapevines. The roots become deformed and fungal infections occur there, which blocks the flow of nutrients and water to the vine.

Question 3

Downy Mildew

Answer 3

This fungi vine disease can destroy grapes and vine vegetation. Between mid-May and late autumn, the aerial parts of the plant can become infected, particularly when the temperature is below 65°F. The symptoms are oil spots and a moldy cover or bright green spots found on the leaves. A white moldy cover is also found on the shoots and the inflorescences. The infection can also reach the berries, particularly the thriving ones, and cause them to dry out and look like raisins. They may also soften and turn a violet-brown color.

Question 4

Powdery Mildew

Answer 4

All aerial parts of the plants can get infected by this disease. Development happens through the entire growing season until late fall. It favors dry years and climates with low humidity and little rainfall. Moldy coats on leaves, inflorescences, and rachis are telltale signs. Berries can become infected in the early stages of their development, with a gray coat covering them and then they dry out afterwards. Infected half-ripe berries usually crack and dry out. The plant’s canes can also become covered with a gray coating with gray-brown spots underneath.

Question 5

Grey Mold

Answer 5

Fruit crops and aerial parts of vine organs are susceptible to grey mold or botrytis. This disease can strike at any time throughout the year, especially when the temperature ranges between 60 and 75°F. Rainy conditions and overly fertilized vineyards can cause the botrytis to appear. The first signs of the disease are spots on leaves that turn brown and begin to rot. The leaves then die, dry, and fall off the vine. Inflorescences can also rot and dry out. On berries, the most devastating effect of the disease is when the fruit becomes covered with the grey mold and begins decaying.

Question 6

Black Rot

Answer 6

All aerial parts of the plant can become infected with this disease. The fungus grows in warm and humid environments between mid-June and late August. The infection likelihood increases when the temperature ranges between 60 and 90°F with a rainy climate. There are first round brown spots on the leaves and the shoots, which die and become dried out. The fungus then reaches the berries while they are still developing. Reddish brown to gray spots appear and then they lose their moisture and shrink into raisins that are brown-black or black-blue in color and have black do

Question 7

Vine Trunk Diseases

Answer 7

Two grapevine diseases in this category, Petri disease and Esca (black measles), are caused by fungal pathogens. They tend to affect old vines that are at least 10 years old but young vines are not immune. Wood and leaves that have contracted these diseases develop unusual discoloration patterns of stripes or sports. The leaves, and then the stems, eventually shrivel in the middle of growing season and grapes end up falling to the ground. The vine then suffers sudden death, which could happen within days after the initial symptoms appear. The likelihood of these grapevine diseases occurring is highest in dry weather that follows after a wet season.

Question 8

Bunch Rot

Answer 8

Infected berries appear soft and watery. In high humidity regions berries become covered in a grayish growth of fungus mycelium. Tight-clustered grape varieties are most vulnerable to bunch rot.

Question 9

Leaf Roll

Answer 9

The symptoms are leaves that curl downward from the shoot and leaf edges that curl under with color becoming red (black grape varieties) or yellow (white varieties) between the veins. Symptoms display from mid-to-late season and often seem more apparent in red than in white varieties. Not all infected vines show symptoms to the same degree, which may be somewhat dependent upon rootstock, variety, clone and other factors. The majority of infections in Cabernet Franc, Pinot Noir, and Chardonnay, for example, show classic symptoms; very few infections show obviously in Riesling; one or more rootstocks may be immune.

Question 10

Anthracnose

Answer 10

Anthracnose is a fungal disease that tends to attack plants in the spring when the weather is cool and wet, primarily on leaves and twigs. The fungi overwinter in dead twigs and fallen leaves. Cool, rainy weather creates perfect conditions for the spores to spread. Dry and hot weather stop the progression of the disease that may begin again once the weather conditions become optimal. The problem can be cyclic but is rarely fatal. - See more at: https://www.gardeningknowhow.com/plant-problems/disease/anthracnose-disease.htm#sthash.UbbguKEv.dpuf