Chapter 20

Managing Vineyard Diseases

Bacterial Pathogens

Grapevine Yellows Disease

Grapevine yellows is a term that is used to refer to several grapevine diseases that are currently attributed to infection of grapevines by pathogens known as phytoplasmas. All varieties of Vitis vinifera are susceptible to grapevine yellows.

Symptoms

Newly infected vines show delayed bud burst and shoot growth in the spring. Internodes are shortened, and shoot development may show a zigzag pattern. Leaves of infected vines exhibit downward leaf rolling which causes the leaves to assume a triangular shape. Infected vines develop a distinctive leaf discoloration and the leaves may become wrinkled and brittle.

Transmission

Leafhoppers primarily transmit the phytoplasma from wild grapevines or other hosts to cultivated vines. The nymphs need to feed on an infected vine or on an infected host plant in order to transmit the disease.

Disease Management

Cultural Practices: When new vineyards are established certified planting material free of phytoplasmas should be used. Vineyards should be routinely monitored for the presence of the phytoplasmas. Because grapevines may be symptomless, active testing of grapevines is recommended.

Chemicals: When a vine is infected with the phytoplasma there is no chemical control strategy but the vector can be controlled with insecticide sprays.

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