Silver scurf (Helminthosporium solani ) is a disease that exclusively affects potato tubers. Although silver scurf does not alter the taste qualities of the tuber, it deteriorates its visual appearance, which affects its marketing. This disease is therefore especially problematic for producers of potatoes intended for the market, because it affects the appearance of the product, even if the internal quality of the tubers generally remains intact. Let’s find out what silver scurf is on potatoes and how to better protect your plants with natural solutions.
Description of silver scurf Disease
Silver scurf is caused by the pathogenic fungus Helminthosporium solani , which belongs to the Massarinaceae family . It occurs mainly on the skin of potato tubers during the storage period, without affecting the growing plants.
Although common, this disease does not usually reduce yields in the field . Its consequences can be more significant after harvest, when storing tubers.
Symptoms are more visible during and after the storage period, which is why silver scurf is usually associated with post-harvest problems . Its appearance alters the visual appearance of the tubers, which can compromise their marketing.
Transmission and development of Helminthosporium solani
Silver scurf is transmitted mainly through contaminated tubers.Â
The fungus Helminthosporium solani can overwinter on crop residues, the surface of infected tubers and even in the soil, although it survives for less than a year.
There are two types of infections:
- primary infections that occur in the field;
- secondary infections that occur during storage.
Infected tubers can then contaminate healthy tubers through air currents in storage.
The disease continues to develop as long as the temperature and humidity remain favorable, especially during the storage period.
What are the conditions that favor the development of silver scurf?
In vegetation, the main source of inoculum is the contaminated plant.
A long delay between cutting the tops and harvesting , more than 4 to 5 weeks, encourages the spread of the fungus.
Silver scabies thrives at temperatures between 20 and 25°C , although temperatures above 5°C are sufficient for its growth.
Poor storage practices also contribute to its development. Humid conditions and temperatures between 5 and 8 °C are particularly conducive to the proliferation of the fungus. Condensation in storage rooms is an aggravating factor.
Symptoms of silver scurf of potatoes
On tubers, silver scurf is observed by light, metallic silvery spots on the skin of the potatoes.
Over time, these spots expand and become covered with fine black dots , which indicate the presence of the fungus’ fruiting bodies. These symptoms are barely visible at harvest, but develop during storage.
Tubers with red skin usually have more pronounced symptoms.
In case of poor storage conditions, it can lead to dehydration and wilting of the tubers. The economic losses associated with this disease come mainly from the deterioration of the visual quality of the tubers, particularly during washing prior to sale.
Integrated management and control of silver scurf
Before culture
- Use healthy plants.
- Crop rotation over a period of more than three years with non-host plants helps reduce the presence of the fungus in the soil.
- Late potato varieties are also less susceptible to the disease.
- The destruction of crop residues and sensitive weeds before potato cultivation helps to reduce the inoculum present.
During cultivation
It is recommended to avoid planting at-risk plots too early and to reduce the time between top dressing and harvesting.
Early harvesting of tubers helps limit their contamination.
During storage
Storage practices play a crucial role in controlling silver scurf. Before storing tubers, the premises must be disinfected to prevent the proliferation of the fungus. At harvest, tubers must be thoroughly dried to limit the development of symptoms.
Once in storage, it is important to maintain proper conditions:
- a ventilated space
- a low temperature
- limited air humidity.
- Condensation should be avoided
Agrobiotop solutions against silver scurf
Coating seed potato plants before planting is an effective solution to prevent silver scurf and other fungal diseases of potatoes such as rhizoctonia or black rot.
We also recommend these soil improvers for your crops :
