2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Black spot is rampant in areas with high air humidity. It affects not only the green organs of vineyards with equal force, but also any lignified areas. Often, grapes are infected with this scourge through the wounds inflicted when the shoots break off or through any other mechanical damage. Unfortunately, crop losses in case of damage by this ailment are very large
A few words about the disease
Black spotting leads to gradual discoloration of the bark on strong perennial wood and on lignified annual shoots. On the very first six to seven internodes, unpleasant specks are formed, and with a particularly strong activity of the disease, such specks can appear on boles with sleeves, as well as on some fruit links. As soon as the thermometer rises above ten degrees, in the faded areas of the bark, the active formation of mushroom fruit bodies begins - pycnidia, which look like countless black dots. If the mycelium grows too deep into infected wood, rotten areas will form on it, severely inhibiting the growth of vineyards and often causing the rapid death of entire branches.
On green organs, the initial signs of a devastating disease usually appear with the onset of June. The ailment is especially strongly attacked by annual shoots - a myriad of oval or round dots of blackish-brown color are formed on them. As the shoots grow, they also noticeably increase, often merging into oblong elongated specks. And the tissue of the vine is slowly dyed in light brownish tones and quickly cracked. The dark edges of the ruptures gradually cork, giving the infected areas an unpleasant scab-like appearance. Often, the pathogen also covers delicate grape leaves. As for the ridges of the clusters and funny antennae, they are much less affected. Occasionally you can find flower caps covered with black spots.
On infected leaf blades, angularly outlined and distinguished by an oval form of necrosis are formed - most often they are located near powerful veins completely painted in black tones. Almost always the necrosis that appears on the leaves are framed by light-colored edges of compacted tissues, when pulled, the leaf blades often break. Premature yellowing is characteristic of severely affected leaves. In some cases, the disease can spread to ripe berries, which immediately acquire a dark purple color.
The causative agent of this harmful misfortune is a higher fungus belonging to the class of deuteromycetes. This parasitically living fungus infects all green organs of vineyards through stomata or wounds. Most often, it is located in the uppermost cell layers. In the spring, when the air warms up to eight degrees or more, countless spores begin to be released from the pycnidia. With strong dew, as well as in the rain, they instantly blur and are subsequently carried along with water droplets. And in dry weather, their distribution occurs with the help of wind, ticks and other various insects. Spores that fall on the green areas of the bushes germinate well at temperatures from fifteen to thirty-five degrees (twenty-three degrees are considered the best temperature) and a relative humidity of at least 85%.
How to fight
It is incredibly difficult to fight black spot, as the mushroom mycelium, deeply penetrating into woody tissues, grows at lightning speed under the reliable protection of grape tissues. Thus, fungal spores are protected from the action of various fungicides by a very solid layer of cells. Accordingly, chemical warfare in this situation gives absolutely no results. It is much more important to focus efforts on combating fungal fruiting bodies, as well as curbing the spread of destructive spores. In the case of severe damage in the fall after pruning or after the foliage has fallen off, it is recommended to treat the grape bushes with preparations containing copper. Drying sleeves should be cut out as quickly as possible. Conducting life-saving eradication treatments, it is extremely important to achieve thorough washing of each bush. And in the spring, fungicides are used at the stage of formation of the first two or three leaves.
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