How To Control Silver Scurf In Potatoes
Silver scurf in potatoes is today a primary concern for growers, breeders, investigators and allied industries. The most effective method to control it and prevent its outbreak in storage is fungicide treatment. But there is a growing interest in protecting the environment, and communities worldwide demand fewer fungicides and put in place other control options. In this regard, the International Journal of Pest Management published in 2020 a review titled Continuous and emerging challenges of silver scurf disease in potato. The present article describes the strategies to mitigate the disease and outlines the areas of study recommended by its authors.
In 2008 FAO declared potato as a Future Food Crop and one of the significant contributors to food security. Many diseases affect potato tubers, but silver scurf is emerging at an alarming rate because it limits its growth and trade value. Its causal agent, H. solani, is a fungus that attacks the potato plants in the field and storage. In this disease, silvery skin blemishes appear on the periderm of tubers.
Considered of minor importance 20 years ago, the disease has become a significant cause for the non-acceptance of potatoes at the commercial level. The lack of resistant cultivars and the emergence of thiabendazole fungicide resistant strains have made this disease much more devastating today.
The following summarizes the different management approaches that have been taken to mitigate silver scurf in potatoes.
Non-chemical management approaches
Essential oils play an important role in plant protection due to their antibacterial, antifungal, antiviral and insecticidal properties. Their advantages over synthetic pesticides include:
- the mixture of active molecules
- low mammalian toxicity
- non-persistence in freshwater and soil.
So an alternative control based on essential oils could be appropriate for potato silver scurf.
Bang led in 2007 one of the most comprehensive studies in this regard. Specifically, he evaluated natural volatiles in 12 essential oils as fumigants to control F. solani, P. foveata, R. solani, and H. solani. From all of these oils, garlic volatiles showed the most potent effects against all four pathogens, both in vitro and in vivo. But due to the contradictory results obtained in both systems, the author does not recommend its use until scientists conduct more comprehensive studies.
Crop rotation is an ancient agricultural management tool. Its benefits include:
- maintaining soil structure and organic matter
- reducing soil erosion associated with continuous plantings of row crops
- reducing plant disease caused by soilborne pathogens.
In 2003 Peters showed in the field laboratory the benefit of 3-year (barley, red clover, potato) over 2-year (barley, potato) rotations for potato production. Both strategies decreased the potato diseases caused by black scurf, silver scurf and dry rot. However, Carter (2003), including Italian ryegrass in a 2-year potato rotation, increased potato productivity compared to rotations that involved red clover or barley. Likewise, in a 2-year potato rotation, red clover was associated with the lowest tuber-borne diseases but the highest populations of specific plant-parasitic nematodes.
With the advancement of nanotechnology, innovative management tools are emerging. For this reason, fungal and bacterial disease management based on silver nanoparticles is booming. That is how the Russian potato industry launched in 2020 a new fungicidal compound, Zeroxxe, that promises to mitigate silver scurf disease. Its active ingredient is a silver nanoparticle.
Biological control is an environmentally sound and effective means of reducing or mitigating pests and pest effects through natural enemies. This system has managed several potato diseases, such as Fusarium dry rot and late blight. Most biological agents are soilborne, and their adaptability to this habitat is much greater than that of pathogens. That is why some researchers have tested their antagonistic ability on fungus H. solani.
Already on the market, a formulation of Bacillus subtilis called Serenade ASO to manage silver scurf in fields. The formulation is successful in reducing its incidence and severity under low disease pressure. It can also delay disease outbreaks in storage for up to five months.
Likewise, the United States Environmental Protection Agency (EPA) has registered a biopesticide called Bio-save (strains of Pseudomonas syringae) for postharvest management of silver scurf.
Potential fields of study
Silver scurf in potatoes is emerging as a primary concern for growers, breeders, scientists, and related industries. On the other hand, the demand for blemish-free potatoes is increasing due to changes in consumer preferences. Both factors put increased pressure to control the disease.
It is essential to have a clearcut understanding of the biology and infection process of the pathogen to frame a management strategy and minimize the growth and reproduction of surviving inoculum of the pathogen.
At present, the disease is pretty well-known, thanks to the investigation conducted globally. Researchers have studied the causal agent, predisposing factors in the field and storage, management practices to mitigate risk, and the mechanisms of infection. But there are still areas of study that the scientific community must address to manage the disease. For example:
Resistant varieties for Silver scurf are required. Potato breeding programs worldwide have used over 3,900 potato germplasm accessions to develop varieties resistant to late blight, apical leaf curl, and potato brown rot diseases. Silver scurf requires similar work.
RNAi-based exogenous dsRNA can be a powerful tool for managing pre-and postharvest conditions in horticultural crops. These new generation dsRNA-based fungicides are environmentally friendly and specific in the management of many diseases. One example is dsRNA-based management of Fusarium graminearum in wheat targeting CYP family mRNA. There is immense potential to use these techniques in the control of storage diseases in horticultural crops.
Genome editing approaches targeting host susceptibility genes against H. solani in potatoes may also be helpful in disease management.
Thiabendazole-resistant strains. The consistent surge of silver scurf is also attributed to increasing thiabendazole-resistant strains. This situation has shifted the researchers’ focus on developing novel fungicide molecules for its pre-and postharvest management. Some authors have found that fungicides like difenoconazole reduce the severity when is applied as pre-harvest seed treatment and storage treatments.
About the author
Jorge Luis Alonso G. is a writer specializing in potato cultivation who writes marketing content for ag-tech companies. He has lived with his family in Canada since 2018.