Black Mold Of Cucumber Leaves

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

Black mold of a cucumber, also called a "burn" of leaves, most often attacks cucumbers growing in open ground or in film greenhouses. And this disease infects all aboveground organs. By the way, old cucumber leaves are attacked first of all. A particularly strong development of the disease is observed with a sharp change in night and day temperatures. Despite the fact that the yield of cucumbers as a result of the defeat of the ill-fated black mold decreases slightly, this scourge must be fought in order to prevent further spread of the infection

A few words about the disease

On cucumber leaves attacked by black mold, tiny spots of light brown color begin to appear, having a rounded, oval or somewhat angular shape. After some time, these spots merge, turning into rather large necrotic spots, reaching a diameter of 0, 4 - 1, 4 cm. Around them, in turn, brown rims begin to form, remaining on the plants even if the dead parts of the leaves are rejected. And a little later, not only the leaves, but also the petioles with stalks begin to dry out and gradually become covered with a cobweb bloom of black. A little less often, the plaque has a dark gray color with a slight purple tint.

The causative agent of a destructive disease is a harmful fungus, the conidia of which are incredibly resistant to a wide variety of moisture indicators. And the persistence of infection occurs on seeds, on greenhouse structures and on plant residues.

The most optimal temperature for the development of a harmful fungus is between twenty and twenty-six degrees. In the event of sudden temperature changes, the plants weaken much faster. If the thermometer drops below ten degrees, the development of chlamydospores will begin on the mycelium (this is the name of the resting stage of the fungus). And on overwintered plant remains, microsclerotia and sclerocial pads are often formed.

To a large extent, the action of the pathogen is enhanced by various mechanical damage received by plants during pinching, pruning and a number of other agro-technological operations.

How to fight

Excellent preventive measures against this cucumber disease are proper pre-sowing seed treatment (more precisely, dressing them), disinfection of greenhouses and replacement or thorough disinfection of the soil (both chemical and thermal). It is also necessary to eliminate all plant residues from the sites. Presowing seed dressing is usually carried out with the TMTD preparation at the rate for each kilogram of seeds - from 4 to 8 g of the preparation. By the way, such processing can be carried out even three to four months before sowing.

As for the resistance of cucumber varieties to black mold, it has not been possible to identify completely resistant varieties so far. However, it was noted that different cucumber varieties are affected completely differently - most of all, the disease covers those varieties that are most often pruned and pinched. This is due to the fact that such trauma to growing crops favors the introduction of infection into plant tissues and its active development in the future. The hybrid Klinsky local F1 and the Dlinnoplodny variety are the least affected by the ill-fated disease.

In order to minimize mechanical damage to tissues and limit the introduction of the pathogen into cucumber tissues, when forming and caring for cucumber plantings, it is recommended to tear off the leaves and pinch it as rarely as possible.

And to prevent the spread of black mold, growing crops are treated with copper-containing fungicides. When symptoms of ailment appear on cucumbers, they are sprayed with a solution of Bordeaux mixture (0.7 - 1%) or a suspension of copper oxychloride (0.5%). After eight to ten days, the treatment should be repeated.