Alternaria Cucumber

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

Cucumber alternaria, also called dry spotting, is most often found in greenhouses (and in film greenhouses much more often than in glass ones) and in a matter of one and a half to two months it can significantly reduce the volume of the crop. Nevertheless, you can sometimes face this scourge in the open field. This ubiquitous ailment develops especially intensively at temperatures up to thirty degrees, accompanied by high air humidity. If you do not take the appropriate measures in time, you can say goodbye to a fairly solid part of the crop

A few words about the disease

Alternaria first affects the plants located closer to the front doors of the greenhouses, and only then the infection begins to move inward. On the lower leaves of the cucumber, you can find tiny and slightly convex dry brownish specks. The largest of them reach about two centimeters in size. Such spots can be located both on the edges of the leaves and in their centers. After some time, the spots begin to deepen and merge into larger formations.

Sometimes a fairly clear zoning is visible on the specks, and a little later, dark brown tufts form on them - this is conidial fungal sporulation. The upper parts of the leaves are often covered with defects in the form of numerous concentric rings. The leaf blades slowly begin to die off, which often leads to sunburn of the fruit. But on the stalks and fruits with petioles, a dangerous ailment, as a rule, does not pass.

The causative agent of cucumber Alternaria is a pathogenic fungus that persists on seeds and plant debris. And it winters in the form of conidia or mycelium. This fungus forms a huge number of dark brown obverse-clavate conidia, equipped with one to four longitudinal septa. And there are usually eight transverse septa in such conidia. In most cases, all conidia fold into rather long, sometimes branching chains, each of which contains from six to eight conidia. And they are carried in greenhouses with the help of air currents, which entails the inevitable infection of new plants. The primary source of Alternaria is the remains of infected plants.

To a large extent, the development of cucumber Alternaria is facilitated by warm weather, as well as moisture accumulating when rain and dew falls or when irrigated by sprinkling.

Quite often, cucumber Alternaria also attacks cantaloupe. It also harms zucchini with watermelons, but to a much lesser extent. Infected plants are almost always more susceptible to heat and wind damage.

How to fight

Unfortunately, cucumber varieties resistant to Alternaria have not yet been bred. So you will have to fight this scourge with the help of the usual phytosanitary measures. It is especially important to strictly follow the rules of crop rotation, returning pumpkin crops to the same plot no earlier than a year later.

As soon as the first symptoms of Alternariosis are noticed on the cucumbers growing in the open field, they are sprayed with "Polyram". The first processing is carried out at the stage of three to four leaves, and all subsequent ones - with an interval of one and a half to two weeks.

In order to get rid of Alternaria in greenhouses, it is recommended to spray cucumbers with one percent Bordeaux mixture or copper oxychloride (0.3%). At the same time, an interval of one and a half to two weeks should also be maintained between treatments.

Such drugs as "Bravo", "Ridomil Gold" and "Quadris" have proven themselves quite well in the fight against Alternaria. The latter preparation gives a particularly good effect if the plants are treated with it either before the first signs of Alternaria appear, or immediately after the first spots are noticed.