2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Powdery scab affects not only potato tubers, but also stolons, roots and subsoil parts of the stems. Especially often with this ill-fated ailment can be encountered in the Tver, Moscow and Leningrad regions, as well as in a number of other areas, characterized by heavy rainfall. In the process of storage, not only the market value of tubers attacked by powdery scab significantly decreases, but also their keeping quality noticeably worsens. And this is facilitated by the causative agents of rot, penetrating into the tubers through the ulcers formed on them. Particularly serious damage is observed with high humidity in storage facilities
A few words about the disease
On the stalks, stolons and roots attacked by powdery scab, the formation of growths of various shapes and sizes begins. Initially, they are colored white, but after some time they darken and quickly disintegrate.
On potato tubers, you can notice the appearance of pustules (as they call deep sores) of a reddish hue, inside which pathogenic mycelium develops. The average size of the pustules is about 6 - 7 mm. After some time, they are opened, and their edges are turned out. As a result of this transformation, the lesions take on a star-shaped appearance. And in the middle of the ulcers, a brownish powdery spore mass is formed. Tubers attacked by a malicious scourge are very poorly stored, because they rot quickly enough. In addition, late blight and dry rot often develop on infected nodules during storage.
The causative agent of the disease is a pseudo-fungus called Spongospora subterranean Wallr. It infects tubers, stolons and potato roots through wounds, eyes and lentils. And the sources of destructive infection are most often manure, soil or infected potato tubers.
Spores of the pathogen often retain their viability for up to three to four years and are resistant to various environmental factors. When they germinate in a humid environment, first zoospores are formed, and a little later - amoeboids, which develop into a multinucleated plasmodium after they penetrate into stolons, as well as into the cells of roots and tubers. A little later, the plasmodium disintegrates into tiny lumps, covered with dense shells and transforming into dormant spores, which stick together into dark spherical glomeruli differing in an irregular shape.
To a large extent, the development of powdery scab is facilitated by a weakly acidic reaction of the environment, increased soil moisture and temperatures in the range from twelve to eighteen degrees. It is especially possible to encounter a pathogen on damp and heavy soils - in such conditions it can persist for up to five years.
How to fight
When growing potatoes, it is extremely important to follow the rules of crop rotation, returning this crop to its former areas after at least four to five years. Liming of acidic soils, drainage of low areas and high agricultural technology, accompanied by the introduction of valuable micro- and macroelements, also help to drastically reduce the infectious background. Plant residues must be promptly removed from the plots. And to prevent the appearance of a pathogen on them, you should use healthy planting material, which is pre-etched with fungicides. An excellent effect is achieved by dressing the tubers with thyram-based fungicides. A fungicide called "Maxim" has also proven itself quite well.
Before you start laying tubers for storage, potato storage facilities need to be treated with a 5% solution of copper sulfate or 3% bleach. Such treatment will help prevent infection of the tubers with a harmful disease. Under no circumstances should tubers attacked by powdery scab be stored for long-term storage, since in this case the likelihood of contamination of healthy potatoes significantly increases.
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