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How are vineyards affected by heavy rains and what other natural foes threaten the vine?

How are vineyards affected by heavy rains? What other natural foes threaten the vine?

vine How are vineyards affected by heavy rains? What other natural foes threaten the vine?
– L.L., Woodland Hills

If it should rain (or hail) during blooming, flowers get destroyed. A light crop results. Rains which arrive late in the ripening period, tend to delay ripening, especially if they are followed by several humid days. This can result in lowered quality, and sometimes leads to complete loss through berry cracking, bunch rot and other maladies. Even without rain, excessive humidity and fog can bring similar harm, as they encourage mildew on the leaves and can cause extensive berry damage.

Another foe is wind damage. High winds can break off tender shoots, resulting in crop reduction. They can rip leaves off, which impairs the vine's ability to produce sugar and mature the fruit. Late in the season, heavy winds can damage ripened grapes by whipping or by exposing them to the sun.

Sunburn poses a threat, as does any extreme temperature condition. When temperatures reach 105° F. or more, grape berries are likely to suffer severely. Exposed to the direct sun in such temperatures, grapes become raisin-like and caramelized in flavor, to the detriment of any wines made from them. In the spring, after the shoots have begun to develop or, as winter approaches, before the vine has gone dormant, below-freezing temperatures can affect the amount or quality of the fruit. They can also seriously damage and even kill vines.

Like any other plant, the vine is prey to all sorts of insects. And it sees its share of troubles from assorted viruses and funguses, even from Botrytis, the so-called "noble mold." This mold turns white grapes into luscious dessert wines, but it renders a red-wine crop unusable if it has affected more than 20% of the grapes.

A promising note: using a fairly simple form of genetic engineering pioneered at UC Davis, it looks possible to develop plants particularly resistant to specific pests, diseases and environmental threats. Vine cells are artificially cultured and then exposed to the phenomenon to which resistance is required. This so-called "mutant selection" system (Mutant Ninja Grapevines?) is less cumbersome and much faster than propagation in the nursery.