2024 Author: Gavin MacAdam | [email protected]. Last modified: 2023-12-16 13:38
Lumpy scab, or oosporosis, most often attacks potatoes in the northwestern, as well as in the northern regions of the country. Slightly less often, this scourge can be encountered in the central Non-Black Earth Region. The ill-fated disease is especially pronounced on sod-podzolic and sandy soils, and slightly weaker - on peat-boggy soils. Among the main reasons for the development of lumpy scab, one can single out air pollution with sulfur dioxide, carbon dioxide, formalin and other harmful substances, as well as a violation of the temperature regime during storage of potatoes
A few words about the disease
Lumpy scab is found about three to four months after the potato tubers are sent for storage. And by the spring, the symptoms of the ill-fated ailment noticeably intensify. On the nodules attacked by tuberous scab, the formation of dark tubercles begins, reaching a diameter of 1 to 4 mm. After some time, these tubercles turn into closed pustules with convex central parts and depressed edges. Thanks to this feature, the disease received another name - smallpox. The bumps are usually located one at a time, but sometimes they can merge. In general, the symptoms of a destructive ailment are similar to those of an ordinary scab in the first stage. If you wet the pustules, they will turn dark brown, and inside will turn grayish-purple.
The causative agent of lumpy scab is considered to be Polyscytalum pustulans - an imperfect fungus, on the mycelium of which pathogenic conidiophores are formed with single-celled tiny conidia arranged in chains. All conidia are cylindrical or oval in shape and are very easily detached from conidiophores.
The best temperature for the growth and development of the pathogen will be between twelve and sixteen degrees. And if the thermometer rises to twenty-five degrees, the growth of the pathogen will stop. Tubers can become infected with a harmful scourge through mechanical damage to the peel, as well as through the eyes with lenticels. And the persistence of infection occurs in the soil and on infected nodules.
Especially often, the ill-fated lumpy scab attacks potatoes during its early harvest - in this case, unripe tubers are most infected. And by the end of the storage period, numerous pustules are formed on their surfaces.
If potatoes are grown for seeds, it is important to remember that the germination rate of infected tubers due to the death of the eyes decreases by about 30 - 44%. In addition, part of the potato sprouts during germination will certainly be affected by a harmful fungus.
As a result of being hit by this scourge, crop losses can be colossal. In infected tubers, the content of vitamin C, protein and starch is noticeably reduced, while the amount of monosaccharides, on the contrary, increases. Tubers weakened by this disease are much more likely to be affected by nematodes, rhizoctonia, silver scab, as well as dry and wet rot.
How to fight
The reduction of the infectious background is greatly facilitated by adherence to the rules of crop rotation. Potassium and magnesium fertilizers should be applied in reasonable doses.
Before harvesting, the tops are destroyed mechanically or chemically. Before you start storing the nodules, they must be thoroughly dried. And directly in the storage facilities, you need to try to maintain the temperature in the range of one to three degrees. Also, in order to reduce air humidity, it is important to ensure their constant ventilation.
Before planting, in 2 - 15 days, it is recommended to spray the seed tubers with thyram-based fungicides. TMTD is also perfect for this. And before placing the tubers for storage, they are sprayed with the Maxim fungicide. However, such products as Tekto or Titusim will also be suitable for treatments.
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