Climatic and Physiological Incidents

Due to its topographical and climatic conditions, this region is frequently subject to direct or indirect weather damage.  Direct threats include frost, hail, cold temperatures, wind, and sunburn—any of which can lead to direct production losses (affecting shoots and/or fruiting structures). Indirect damage can range from mild to severe depending on the vines' phenological stage—which, in turn, is highly related to regional temperature and rainfall patterns. This climatic damage risks interfering with the vine's normal physiological processes (flower differentiation, fruit set, and so on).

The presence of numerous rivers and valleys ranging from narrow to wide creates a wealth of microclimates throughout the Vinhos Verdes region. Thus, an event may strike one subregion while sparing another.

Frost

The most dangerous frost events take place in the spring, just after budbreak, when the buds and shoots are still highly tender. Clouds and wind have protective functions. Clouds return radiated heat to the earth while the wind mixes the warmer air above with the colder down below. As a result, frost only occurs on clear, cold nights without wind. Lower lying vineyards with insufficient atmospheric drainage are most frost-prone, as are those with sandy, loose, or rocky soils that cool very quickly.

Frost prevention measures include avoiding planting vines in low-lying areas with poor air drainage. In addition, soils should be kept under a mowed cover crop, since high weeds and freshly tilled soil cool down more quickly. Some protection systems exist which, when temperatures trigger an alarm, automatically dispense water from an overhead system in the vineyard. This measure is, however, beyond the means of some of those operators who indiscriminately plant their vineyards in inappropriate locations. The main cultural preventative measure entails pruning susceptible vines later and beginning instead with later-budding varieties (such as Trajadura and Vinhão).

If frost occurs early in the growing season killing the primary bud, the secondary buds left during pruning will burst; and, albeit less fertile than the destroyed bud, they will ensure sufficient growth for pruning in the following year. The frost will also stimulate the crown buds near where the cane meets the old trunk to break. Later frost (when flower clusters are visible or separated) will lead to leaf loss and the growth of suckers.  Were the frost to occur later (when clusters are visible or separated), the leaves will be lost and lateral shoots will push out. Several measures must be taken following a severe frost: the fruiting cane or the green shoot must be pruned and the shoots thinned out, especially those from the crown buds. Foliar fertilization should be applied later to replenish growth.

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Cold

Cold snaps during the growth cycle can be harmful at two stages: spring and summer.

Cold springs lead to slower plant growth and the inflorescences may stagnate fully or partially, dramatically reducing that year's production. Nothing can be done.

When summers fail to bring the normal hot and dry conditions, flower differentiation can be negatively affected, meaning the latent buds become leafy rather than floral, which compromises the following year's budbreak and production. Nothing can be done.

Wind

Strong winds can be particularly harmful up until bloom or fruit set, since the shoots always grow vertically independently of the future canopy orientation. Only when they have reached a certain weight (usually when 10-12 leaves have sprouted) do they then begin to droop over naturally. By then, the shoot has already attached to the cane and lignified, and will resist breakage. Whether coming from the south in advance of rain or, otherwise, from the north, winds in this pre-floral period cause breakage of the new green shoots and production losses.

Some varieties are more susceptible to wind damage than others. Due to its propensity to shatter (locally known as desnoca), Loureiro is particularly sensitive to wind when grown on overhead training systems. The same is true for Alvarinho.

Hail

Hail is probably the most dangerous climatic event for vineyards, as it can occur at any point throughout the growth cycle. From budbreak to harvest, it can knock off buds, shoots, inflorescences, clusters, or berries, as well as wounding the canes or cracking berries. Contrary to the case of frost, no measures exist to protect against hail, since it happens sporadically and in highly localized locations.

Hail during the height of the growth season often requires the removal of damaged shoots and tipping back young shoots to stimulate lateral shoot growth and restore the vine’s leaf area potential. Anti-botrytis treatment should be applied together with a nitrogen soil fertilizer. In the event that leaves are still on the vine, a foliar fertilization with calcium should be applied to enhance healing. 

Downpours/Heavy rains

Heavy rains or cloudbursts, usually associated with thunderstorms, are especially damaging in summer during ripening. They can knock branches, entire clusters or even leaves to the ground, leading to significant crop losses.

Sunburn

During periods of high temperature and low humidity, grape clusters are susceptible to being burnt by the sun. When trying to prevent sunburn, it is better to avoid over thinning the leaves. Only the shadier side of the canopy should be thinned out, and never remove lateral shoots. 

Some varieties such as Vinhão are more susceptible, as are younger vines and those planted in poorer and drier soils.