Black Scurf in Potato: Hidden Soil Disease Reducing Tuber Yield and Quality

Using correct fertilization schedules, irrigating correctly and caring for the potato crop well does not always guarantee an adequate yield for many growers. Black scurf in potato is a soil-borne disease that is often overlooked until harvest when sprout rot, common scurf and other diseases cause significant challenges. The first symptom presented by farmers is usually weak emergence, irregular stands or delayed plant growth in the field, but the actual problem is only seen with the presence of black patches on harvested tubers. They cause market loss because of their dark colour and also decrease potato qualities for storage and seed.

Potato scurf disease is often confused with other diseases and deficiencies because black scurf of potato symptoms occur early but in the soil. Rhizoctonia solani affects young sprouts or sub surface stems before plants reach maturity. As a consequence, root areas are poorly developed, plants uptake less and fewer nutrients, and the size of the tubers decreases during the season. A new discovery is how to treat rhizoctonia solani fungus problem can build up to a large scale. As a result, more potato growers are interested in organic seed treatments for potatoes due to the gains in soil fertility and better seed emergence.

A comprehension of the true nature of black scurf in potato fields

The greatest difficulty in dealing with rhizoctonia solani is that it exists in the soil unnoticed, and in infected tubers, at least for a time. A number of farmers are unaware that they are carrying the disease from one season to the next by using infected seed potato which looks healthy on the outside. When grown in cool, moist soil, fungus activity takes place and the fungus infection can infect the sprouts before they shoot up above the soil. That's the reason why black scurf is tending to be more common in potato fields with poor drainage or in fields where potatoes are cultivated every year.

Poor plant stand and/or black scurf of potato symptoms will not be noticed by most growers until after harvest. Unlike bacterial diseases, the removal of the fungus is difficult once soils are contaminated and held in crop residues and organic matter. Because there is a loss in yield if the disease occurs, research into the how to treat rhizoctonia solani fungus is taking a greater interest in on-farm preventive management rather than a rescue approach later in the season. To minimise infection pressure and ensure potato productivity, it is essential to understand the disease cycle, its survival and spread.

Early Field Signs Farmers Should Never Ignore

It is important to detect black scurf of potato symptoms at an early stage in order to take adequate management measures before substantial yield loss occurs. Some farmers are closely observing fields to detect the various signs of uneven emergence, weak sprouts, thinned stems and slow plant emergence shortly after planting. As a result of infection, plants may become stunted due to the attack of the fungus on the underground stems and decreased root growth. Where tubers develop stem cankers the stem's strength is lowered causing fewer tubers.

Hard black fungal masses (scurfs) which form during harvest on the surface of the tuber are one of the most obvious symptoms of infection with black scurf in potato. They are survival bodies inherent in the rhizoctonia solani and although their appearance is similar to that of soil, they cannot be readily washed off. Both these symptoms are mistaken for those of poor nutrition or quality of seed and are thus not properly addressed. This is why there is an increasing interest in organic seed treatments for potatoe amongst growers wishing to achieve early protection against infections that occur in the soil and to have a crop set up naturally.

How Black Scurf in Potato Spreads Rapidly Through Soil and Seed Potatoes?

The amount of Rhizoctonia solani present in potato fields is greatly affected by planting conditions and seed quality. One of major sources of introduction of disease-Infected seed Potato into clean fields. The fungus spreads in the soil by contact with infected seed and infects adjoining plants in early stages of growth. Fungi develop in the wet soils, with too much moisture, compacted fields and in conditions of cold soil.

The chemical control of black scurf of potato is high level and extensive in use by many farmers; however, if conditions persist as disease favours then disease pressure may be high. Lack of adequate drainage and year after year cropping of potatoes can contribute to the longevity of the fungus in the soil making control more challenging from year to year. Potato seed treatment fungicides can help to lower the risk of initial infection, but can result in only partial control of disease under extremely heavy conditions. Growers who have experienced multiple incursions of black scurf in potato are now mindful of reducing the longevity of the fungus in the soil through other improved soil management practices, disease field sanitation and potato rotation.

Why Traditional Fungicide Programs Sometimes Fail in Potato Fields

Many growers spend a great deal on disease management regimes based on chemicals yet find results are difficult to be consistent. A big problem is that the best fungicide for potato seed treatment are effective primarily in contact application during early planting operations and do not give long term control if environmental conditions favour the growth of fungi. Despite fungicide application, the disease is likely to resert if the soils are heavy, conditions are moist and potato is grown continuously.

The results are sometimes inconsistent in trials by potato farmers looking for the most effective potato seed treatment fungicides, a situation linked to a reduction in the effectiveness of these chemicals under high disease pressure. The same products may also not work as optimally in the future, potentially as a result of repeated use over time. In the process, growers are starting to understand that solely chemical program black scurf of potato treatment methods for black scurf of potato disease may not provide adequate disease control for the long term. Integrated potato management is an approach that is growing in importance, helping the management of the soil, the survival of fungi and its biology.

Farmers have a poor economic motivation for biological seed treatments

As a result, biological methods are being employed as a solution to potato diseases, as well as soil health, and are gaining traction amongst growers. Multiple farmers are investigating as what biological seed treatments are available for potatoes that are beneficial to soil microbes and won't negatively impact beneficial soil organisms. Biological treatments are not the same as chemical treatments in the sense that they don't stimulate microbial competition all in one place around the seed area but they do.

The use of modern organic seed treatments for potatoes can help to establish glutathione through improved microflora around germ/tubers. These pathogens interact with fungal pathogens, help suppress them and enhance early establishment of roots. Biological methods for black scurf of potato treatment usually result in better emergence, root system development and vigor during the initial growth of the crop. Beyond disease control, biological methods contribute to the sustainability of soil giving protection to microbial diversity and not relying on multiple applications of chemicals.

How BIOCOAT helps the farmers save potato seed tubers naturally?

How to treat rhizoctonia solani fungus? BIOCOAT Potato Seed Treatment is now being used by many potato farmers as part of their preventative disease management programme. Biological products that enhance seed protection by strengthening the plants' immune system are drawing interest from farmers who want viable solutions to treating rhizoctonia solani fungus, not devoid of synthetic chemicals. BIOCOAT is a biological mixture that contains helpful microbes that adhere to the exterior of the seed tuber and the environment around the tuber and root.

These healthy bacteria create a layer of protection, reduce fungal growth and aid in healthy sprouting and root development. With approximately two decades of experience in organic seed treatments for potatoes, growers frequently report higher establishment levels, better root development and lower levels of disease during the growing season. Biological seed treatments, such as BIOCOAT for potatoes, can be a useful solution where farmers are interested in what biological seed treatments are their for potatoes to not only prevent disease but also to improve soil biology. This form of biological protection can lessen the likelihood of infection risks early in the season and aid in improved plant growth throughout the season.

Development of a sustainable plan for dealing with black scurf to improve yields of potatoes

Accompanying any black scurf of potato treatment success must be other management strategies. Farmers that have reliable disease control, generally use a combination of practices, to form one integrated strategy for the whole field. Early management of black scurf starts with the commencement of certified disease free seed, crop rotation, good drainage and the adequate planting under appropriate soil condition. Maintaining adequate soil moisture, and avoiding too cold, compacted planting sites can greatly reduce disease pressure.

As growers look for “long-term” answers on how to treat rhizoctonia solani fungus, a combination of biologicals and better agronomic practices is becoming more common. Crop rotation is used to decrease the presence of the fungus in the soil, balanced fertility and the improvement in the general cleanliness of the field promotes stronger growth of the crop. The best fungicide for potato seed treatment is still an accepted treatment for many farmers, but is now being used in combination with biologically based methods for more sustainable protection. With an integrated management plan over time disease carryover is reduced, soil health is increased, crop establishment is enhanced and potato yields are improved season after season.

Reference: 

• Chaudhary, Sorabh, et al. "Black scurf of potato: Insights into biology, diagnosis, detection, host-pathogen interaction, and management strategies." Tropical Plant Pathology 49.2 (2024): 169-192.
• Sharma, Sanjeev, et al. "Soil-and tuber-borne diseases of potato." Approaches for potato crop improvement and stress management. Singapore: Springer Nature Singapore, 2024. 179-231.