Dry Phoma Rot Of Potatoes

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

Dry phoma rot of potatoes occurs wherever potatoes are grown, affecting both the tops and tubers with the same force. And this unfortunate attack manifests itself in the form of ulcers or numerous necrotic foci. There are several different forms of this disease, but they are all equally harmful and lead to a noticeable reduction in the volume of the long-awaited harvest

A few words about the disease

At the very beginning of the development of dry phoma rot of potatoes on the surfaces of potato nodules, the formation of slightly depressed and slightly rounded spots of a dark color, bordered by distinct boundaries, begins. A little later, these spots increase, turning into sores equipped with tightly stretched peels. Affected pale brownish plant tissues begin to slowly spread inward in the form of cones. They are separated from healthy tissues by narrow stripes with a more intense color. If you cut the tubers, you can see that all infected tissues are characterized by a predominantly light brownish color.

The peel on infected potatoes quickly shrivels and begins to crack, and pathogenic pycnidia emerge from time to time through the peel of the tubers. At the next stage in the development of dry phoma rot, tuber tissues begin to stain in darker tones, up to black. And inside the nodules, you can see voids, from the inside covered with a grayish bloom of mushroom mycelium. When the disease enters its final stage, it thickens noticeably, the infected tissues dry out, and the pycnidia covering the nodules quickly become clearly visible. Often there are almost completely empty nodules filled only with mushroom mycelium and a loose dead dried mass.

As for the stem form of the disease, it manifests itself mainly during the flowering period of potatoes. Small specks begin to appear on the stems near the leaf petioles, on which brownish pycnidia form a little later. And the necrotic form of the disease is characterized by the appearance on potato nodules of small sores of a dark color and of the most diverse form. In terms of external signs, the necrotic form is somewhat reminiscent of late blight manifestations, however, in nodules attacked by dry phoma rot, the internal tissues are painted in soft yellowish-pinkish tones, and in tubers covered with late blight, all internal tissues have a rusty-brownish color. In addition, in a necrotic form, the fungus does not penetrate very deeply into the tubers - only by 4 - 6 mm. There is also the so-called "eye" form of the disease, with the defeat of which in the places of the eyes appear unpleasant depressed spots.

The causative agent of dry phoma rot is a pathogen called Phoma exigua. During the period of growing potatoes, the infection is easily transmitted by wind and rain, and during storage, its transmission occurs from one tuber to another through any mechanical damage or through eyes with lenticels.

To a large extent, the development of this harmful scourge is facilitated by damp and cool weather during harvesting, high temperatures and humidity during storage, as well as the various mechanical damages mentioned above.

How to fight

The main preventive measures against dry phomous rot of potatoes are observance of crop rotation and minimization of all kinds of mechanical damage. When planting, it is necessary to use only healthy planting material, which is recommended to be pre-treated with the "Maxim" fungicide. It is important to systematically disinfect storages and containers, and in the storages themselves, it is necessary to maintain optimal humidity (no more than 80%) and a proper temperature regime - for twenty-twenty-five days after cleaning, the temperature is kept within the range from eighteen to twenty degrees, gradually reducing it to two - three degrees.