Ascochitosis Of Cucumber

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

Ascochitosis of cucumber is otherwise called black microspherellous stem rot. Basically, you can face this trouble in greenhouses. And in the open field, ascochitis is much less common. Depending on the conditions of this harmful ailment, yield losses can reach from thirty to fifty percent. Ascochitis is activated most often in April - during this period there is no opportunity to fully use the ventilation of greenhouses, and the temperature and humidity established in them favor the development of a destructive scourge

A few words about the disease

On the cucumber stalks attacked by ascochitosis, the formation of numerous rounded specks begins. Initially, these spots are characterized by a greenish or gray-green color and some wateriness, however, as the infection develops, they slowly turn brown, and at the end of the development of the disease they turn white. All spots grow rather quickly, covering the entire stems. And the integumentary tissues gradually crack, as a result of which the organs attacked by the disease begin to exude small droplets of exudate, colored brownish or milky. As for the vascular tissues, they are covered by the disease only in rare cases, and therefore infected plants for a long period can not only vegetate, but also bear fruit.

Often, ascochitis can manifest itself in the nodules of the stalks, as well as on rather long "stumps" that are formed after the removal of leaves and shoots with fruits. Infected tissues are almost always densely covered with black pycnidial dots.

Fruits with leaves can also be affected by ascochitis. The leaves are usually affected as soon as the cucumbers begin to bear fruit, and the harmful attack begins to cover them from the edges of the leaf plates. The affected areas are covered with vague spots of a rather large size (up to four to five centimeters in diameter), and chlorotic zones can be observed along their periphery. The leaf tissues located in the zone of spots first turn brown, and a little later they are painted in light yellow tones and are covered with pycnidia. In this case, pycnidia can be arranged in patterned concentric rows or chaotically. Infected tissues dry out and begin to crumble, as a result of which the leaf blades quickly die off.

And on the fruits of the ill-fated misfortune can manifest itself even in three different forms. In the first case, the infection spreads from the tops or from the bases of the fruit. The diseased tissues dry out slightly, taking on the appearance of boiled ones, but at the same time retain the firmness of their structure. A little later, they become covered with pycnidia, after which the fruits begin to blacken, mummify and decompose as with wet rot. And on the surfaces of cucumber testes, gum-secreting sores or cracks often appear. In the second case, tiny (with a diameter of 3 to 5 mm) and densely covered with pycnidia dry sores appear on the greens, gradually deepening into the cucumber tissues. And the third form of ascochitis is manifested in the "rusting" of the cucumber pulp. First, the upper parts of the fruits turn white, and then specks of rusty color appear inside them. Some time later, these spots become licky, and the development of secondary bacterial rot begins.

At the fruiting stage, ascochitosis is quite clearly manifested on all plant organs. It is noteworthy that it is extremely rare to encounter it on seedlings.

The causative agents of such an unpleasant ailment are considered to be parasites of an optional type. As a rule, they are capable of infecting extremely weakened plants. In this case, the infection in the soil, as a rule, does not persist, since the pathogen cannot multiply in such conditions. Its preservation usually occurs in seed material, on greenhouse walls and in plant debris.

How to fight

The best preventive measures against ascochitis of cucumber are the observance of crop rotation and the cultivation of slightly affected varieties.

During the growing season, cucumber plantings are sprayed with 1% Bordeaux liquid or 0.3% copper oxychloride. A good effect is also given by spraying with a weak solution of copper sulfate (for ten liters of water - 5 g), to which 10 g of urea is added. It is recommended to periodically disinfect the inner surfaces of greenhouses with a formalin solution (2 - 5%), and steam or fumigate the soil.