Susceptibility to lenticel breakdown is often determined in the orchard, but the symptoms usually develop or become worse after harvest. Lenticels begin to dry out or crack, and the disorder is characterized by dark or blackened lenticels, or small superficial brown spots circling the lenticels. These lesions become sunken over time and eventually allow pathogens to enter, causing rots (Figure 1).
Micro-cracks develop in the fruit cuticle when apples are growing quickly. Lenticels are most susceptible to cracking and desiccation because they are exposed and provide access points for irritants and water, which eventually lead to cell death and pitting. Irritants can be dust, orchard sprays, agri-chemicals, or salts dissolved in water, especially when there are rapid large temperature changes as well.
Plenty of lenticel breakdown was observed in Ontario apple orchards during the 2020 growing season (Figure 2). According to Kristy Grigg-McGuffin (OMAFRA), researchers within the Great Lakes region saw symptoms like lenticel breakdown in previous years related to the use of certain methyl benzimidazole carbamates, or Group 1 fungicides during periods of rapid fruit growth. However, it is not known at this time whether the currently registered Group 1 product, Senator 50 SC (thiophanate-methyl) can cause this type of injury.
Other pre-harvest factors that increase the risk of lenticel breakdown include: mineral imbalances, especially high (K+Mg)/Ca and N/Ca ratios; rapid changes in weather resulting in rapid fruit growth; and advanced fruit maturity at harvest, like when delaying harvest for color development. Lenticel damage is set-up pre-harvest when fruit are growing, but often disorder symptoms are expressed after postharvest handling.
Apples harvested with advanced maturity are highly susceptible to lenticel breakdown. Extended storage duration for the maturity of the fruit will also increase susceptibility.
Dump tank chemicals, soaps and detergents, waxes, and 1-MCP treatments can further aggravate lenticel breakdown. A large temperature difference between cold fruit and warmer hot water on the packing line will also exacerbate the problem.
Adhering to good pre- and postharvest practices can help reduce the risk of lenticel breakdown. Shorten the storage period for high risk fruit and minimize large temperature swings. Harvesting at optimum fruit maturity is a very important key factor!