Anthracnose, caused by Elsinoe ampelina Shear, is an important disease of grapevines in [he Auckland district.Young leaves, stems, and berries are susceptible to infection. Fully expanded leaves, and stem internodes bearing them, are highly resistant or immune. Berries become highly resistant, though not immune, about ·50 days after anthesis, when soluble solids have risen above 5-7% in the juice.Wetness periods necessary for infection range from 7-10 hr at lrc, in spring, down to 3-4 hr at 21°c, in summer. Conidia are produced in abundance 14 days later at lrc, and, after 5 days, at 21°c. Spore flights of up to 7 m, in wind-borne rain-splash drops, were detected.
Ascospores of Venturia inaequalis (eke.) Wint. are not released from perithecia unless the perithecia are wetted. Greater numbers of ascospores are released when wetting occurs in light than when it occurs in darkness. Greater numbers are released when perithecia have been warm, or in a humid atmosphere, before they are wetted, than when they have been cold, or in a dry atmosphere before they are wetted. High numbers of ascospores in orchard air associated with daytime rains, compared with the low numbers associated with night rains or dew, are the result of the influence of light and of higher temperatures on ascospore release.
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