Alternaria Grape

2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38

Alternaria grape, also called olive spot, can be found in almost all vineyards. Moreover, over the years, its harmfulness increases markedly. Alternaria affects not only grape leaves, but also shoots with berries. To a large extent, the development of this misfortune is facilitated by rather humid and very hot weather. And the most pronounced symptoms of a harmful disease appear in the second half of the growing season. It also poses a serious danger when storing grapes, therefore, it is necessary to fight this disease very actively

A few words about the disease

The growing grape shoots and leaves attacked by Alternaria begin to become covered with silver specks, which inexperienced gardeners can easily mistake for the manifestations of powdery mildew. And after some time, all the spots darken, turning into brownish shades. If the Alternaria attacked the grapes with special force, the leaves often turn black and subsequently dry out. And during the rainy season, grape leaves are often covered with mold. As for the shoots, they are usually especially strongly affected in conditions of a protracted spring.

On ripe grape berries, the symptoms of the ill-fated misfortune appear in the form of a light metallic sheen. A little later, the development of a dark gray mushroom bloom begins on their surface. The berries acquire a very unpleasant aftertaste and begin to shrivel. Having stopped ripening, the grapes slowly die off. Accordingly, one can only dream of a good harvest in this situation.

The causative agent of the unpleasant disease is a very harmful fungus representing the genus Alternaria and overwintering in the form of mycelium and conidia in infected plant debris and in the bark. Sometimes it can overwinter in the bark and soil in the form of conidia and microsclerotia.

Often, vineyards attacked by Alternaria additionally damage Phomopsis. If this happens, both ailments will only exacerbate each other's course. And in the event that infection with a harmful misfortune occurred at the stage of harvesting, the pathogen will certainly develop during the storage period, and without much difficulty will spoil the entire harvest.

In order not to confuse Alternaria with powdery mildew (that is, ordinary powdery mildew), the infected part of the leaf or shoot is placed in a saucer of water, after which it is covered with a moistened glass and sent to a sufficiently warm place for several hours. If the shoot or leaf is affected by Alternaria, then they will be covered with an olive velvety bloom. If this does not happen, then this is not an alternariosis, but something else.

How to fight

The main preventive measures against alternariosis of grapes are high agricultural technology and timely elimination of post-harvest residues. And when the first symptoms of a harmful misfortune are found, the vineyards are sprayed with a two percent solution of Bordeaux liquid.

As a rule, in most cases, protective measures against the ill-fated illness begin to be carried out in the spring. The fact is that the most important period in the fight against this scourge is the stage of opening the first pair of leaves, and it is very important not to miss this moment. In order to protect against a harmful disease, various contact fungicides containing copper or mancoceb are used (Ridomil Gold, Ditan and others). And when the berries begin to close in bunches, they begin to use such systemic insecticides as Quadris, Kolfugo Super, Skor, Rapid Gold or Cabrio-Top. At the same time, it is recommended to maintain an interval of one and a half to two weeks between treatments. Treatment of vineyards with "Trichodermin" also gives a good effect. You can also use drugs such as "Oxyhom" or "Garth".

The grapes should be harvested as quickly as possible, and the bunches should be stored at optimum humidity and temperature.