Chapter 21

Managing Vineyard Diseases

Viral Pathogens

Grapevines are susceptible to a large number of plant viruses. Viruses are tiny, replicating pieces of genetic material (single- or double-stranded DNA or RNA) covered with a protein coat. Once inside the plant cell, the nucleic acid portion directs the plant cell to produce more virus nucleic acid and virus protein, disrupting the normal activity of the cell. Some of the symptoms associated viruses include reduced growth that results in stunting, malformation of leaves or growing points, distinct yellowing only of veins, and cup-shaped leaves. Some of these viruses are widely distributed wherever grapevines are grown, and others are present locally or in a limited geographic range. Depending on which virus is involved, the disease may be spread from infected vines to healthy vine: 1) mechanically on workers' hands or tools; 2) by aphid, thrips, whitefly, leafhopper, mite, or nematode feeding; or 3) through vegetative propagation. In grapevines, the virus will spread systemically to all parts of the vine (roots and vegetative parts). Once introduced, it is impossible to eradicate a virus from a vineyard.

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