The Causes of Three Kinds of Grape Atrophy Symptoms and Their Control Measures

The maturing process of grapes includes changes in color and structure, accumulation of volatile substances, and sugar. Only when these aspects are in harmony can an ideal high-quality grape grow.

On the contrary, some problems in the growing season will also make the fruit poorly developed, the most obvious of which is the atrophy of the fruit. Each kind of atrophy is caused by a specific cause, and the fruit will have different manifestations.

Sunburn

Lack of irrigation, open scaffolding, excessive foliage removal, and too little nitrogen fertilizer application can cause fruit sunburn. And the sunburn that faces the west (in the case of the Washington-producing region) is more serious.

If the grape is sunburned before the color change period, the fruit will dehydrate until it withers; the grape will dry completely when it is severely sunburned after the color change period, until it becomes raisins.

Management measures: Sunburned grapes can be used to make certain style-specific wines. Since sunburn is mainly caused by the lack of canopies, we can strengthen management in this area by adding protective shields to reduce the amount of time the grape receives direct sunlight (especially in the afternoon). At the same time, try to keep some leaves above the ear when sparse. .

Seasonal dehydration

Since this symptom of wilting usually occurs in the early stage of fruit ripening, its effect on yield is very serious.

The cause of end-season dehydration is still uncertain, but it is certain that this phenomenon is closely related to the termination of sugar accumulation during ripening or the return of moisture. Polygonal depressions form on the surface of the grape, like a golf ball.

Although the surface is wrinkled, the fruit is very complete and the fruit stems are still healthy (see Figure 2). Dehydration results in a drop in fruit weight, so the vineyards will cut production. In contrast, the accumulation of sugar continues as the weight decreases, so the quality of the grapes is not affected, and the grapes after shrinking are more suitable for winemaking.

Management measures: Under normal circumstances, this condition will cause dehydration of grapes about 15-30%. Unlike sunburn, prevention of end-season dehydration is a very difficult task because its cause is not yet clear. When the symptoms are severe, these fruits can be used to make high-end sweet wines. When the symptoms are mild, you can ignore it.

Spike necrosis

Grape ear stem necrosis is another atrophic disorder that occurs after the color transition period, and is susceptible to disease before and after grape maturation. It usually appears in the dark part with shading of foliage, and from the appearance point of view, it causes black lesions and spreads to any part of the spike (the collective name of the stems, including the wing, the flower axis, and the fruit stem).

These wounds will continue to spread, causing necrosis and the loss of green pigment, which is the main feature of ear stem necrosis. And ring wounds also block the transport of water, nutrients, and sugar. Therefore, the fruit at the top of the ear will dry out and shrink, forming raisin-like folds (see Figure 3).

Among all maturation disorders, ear stem necrosis is the most studied disorder. Its production is related to the vitality of the vine, its high yield, serious lack of protective measures, excessive precipitation (high humidity) and lack of calcium, magnesium and other minerals.

Compared with dehydration at the end of the season, the necrosis of the spikes makes the sugars of the fruit highly concentrated (up to 43°Brix). This grape is not suitable for brewing ordinary wines and can be used to make wines that are particularly resistant to storage.

Management measures: Excessive occlusion and low-temperature climate at maturity may aggravate the situation of ear stem necrosis. Some of the measures of European farmers have shown that the addition of nutrients can suppress ear stem necrosis.