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FROST OR LOW TEMPERATURE Frost may induce a non-lethal injury to the vines that may be confused with herbicidal damage or virus-induced symptoms. Frost injury is mostly associated with temperature drops at high altitude and in northern growing regions. Sensitivity to frost varies with varieties. Leaves collapse and show a wilting appearance; affected areas with appear black when wet and brown when dry. Around freezing temperatures may cause irregular growth and graying to browning across the blade. Slight damage may cause a yellowing (chlorosis) of leaf blades and veins. Veins may be mottled. Young leaves may have dark (necrotic) specks. Symptoms of affected tissue persist through season even when the rest of the leaflet continues to grow. Early season exposure slows vine growth. Symptoms appear similar to injury by PGR-type herbicide. Sensitivity to
frost varies with varieties. Tolerance to frost may be bred from wild
species into commercial varieties in the future. Foliar-applied cytokinin-like
PGRs may give some protection against injury but more research is needed.
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