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Apple farmers are no strangers to crop diseases. Apple scab, black rot, frog-eye leaf spot, leaf blotch, and fire blight are some of the common diseases that growers try to prevent each season. While some of these diseases might only appear on apples in the post-harvest stage, infections commonly occur in the field during the growing season, which is why growers vigilantly make sure their crops are protected.
Dr. Shawkat Ali, in the orchard at the Kentville RDC, examining an apple tree.
For decades, growers have relied on fungicides and antibiotics to prevent crop diseases. However, research has shown now that extensive use of these products can lead to pathogens (microorganisms and viruses that can cause diseases within the plant) developing resistance to the product, making it ineffective against diseases. Additionally, these chemicals can kill both beneficial and harmful microorganisms without distinguishing between them. Preventing diseases is crucial for the success of the crop, which is why research scientists Dr. Shawkat Ali and Dr. Pervaiz Abbasi (retired) at Agriculture and Agri-Food Canada (AAFC)’s Kentville Research and Development Centre (RDC) in Nova Scotia initiated studies to explore alternative sustainable disease management solutions.
Most recently, Dr. Ali, Dr. Abbasi and graduate student, Shayne McLaughlin (Dalhousie University) were researching how to reduce the amount of fungicide treatment applied to apples, by using a sustainable alternative product, salicylic acid. Salicylic acid is a plant hormone that activates a plant’s natural defense mechanisms, so the plants’ immune system can fight off harmful pathogens. Dr. Ali and his team were curious to see if salicylic acid could be applied to apples as an alternative to chemical fungicides, particularly Honeycrisp, as it is the most common cultivar grown in the province. Dr. Ali and Dr. Abbasi partnered with the Nova Scotia Fruit Growers’ Association in 2019 to put their theory to the test. Since growers generally apply fungicide sprays 12-14 times over the growing season, Dr. Ali wanted to see if incorporating salicylic acid into the farmers’ disease prevention rotation could significantly prevent apple scab, bitter rot/frogeye leaf spot and black rot diseases as well as reduce the amount of the standard fungicide applications in the field.
In the Kentville RDC apple orchard, Dr. Ali and the team selected two plots. On one plot, they reduced the fungicide application and incorporated the salicylic acid treatment. On the second plot, the normal fungicide application was applied to the apples. Over four growing seasons, the Honeycrisp apples were sprayed, harvested, and examined. Following four months of storage, the apples were examined again for post-harvest diseases. Dr. Ali and the team also examined the apples’ characteristics for fruit quality, including average weight, total sugars, firmness, titratable acidity and maturity.
A few apple growers in Nova Scotia, Prince Edward Island and New Brunswick also tested this practice on their farms. Salicylic acid was sent to the volunteers, and the growers were instructed to replace four of their conventional fungicide sprays with the salicylic acid. Once the season was over, the growers sent apple samples from these trials to Dr. Ali for harvest and post-harvest examination and disease assessment.
After examining the apples, the team found that salicylic acid had no negative impacts on the quality of the fruit at harvest and after post-harvest storage. He also found that growers could reduce their conventional fungicides application over the course of the growing season by 29-33% by using this method. Although this treatment did not eliminate the need for fungicides completely, Dr. Ali says that incorporating salicylic acid can reduce the number of fungicide applications while still providing the same amount of disease control.
Since salicylic acid has shown positive results in preventing diseases and reducing fungicide applications in Honeycrisp apples, Dr. Ali hopes to expand this research in the future by testing this method on different apple cultivars. He hopes that if the results continue to be positive, a commercial product could potentially be developed providing growers with an alternative to reduce conventional fungicide treatments.
“Our lab is extremely interested in finding sustainable solutions for disease control in tree fruits and small fruits. There are many benefits for fungicide reduction and wider adoption of these methods could reduce the expenses for farmers, as the applications of fungicides can be expensive. Over time, pathogens build a resistance to fungicides and reducing the number of applications will help to prevent resistance in pathogens causing disease in crops. Ultimately, it’s a win-win solution for growers, consumers, and the environment.”
- Dr. Shawkat Ali, research scientist, Agriculture and Agri-Food Canada
Photo gallery
A photo of bitter rot, a common disease in Honeycrisp apples.
A photo of frog-eye leaf spot disease.
A photo of apple scab disease on a Honeycrisp apple.