A Special Delivery: Bitter Pit, Crop Nutrition and Calcium Transport

Life is good for Emma Grant. Just 25 years old, she is already in her third season as the Orchard Manager at 2,500-acre Cherry Bay Orchards in Suttons Bay, MI. While killer frosts, spotted wing drosophila, and leaf spot can wreak havoc on her cherries and apples any given year, she typically takes solace knowing she has either fought the good fight or rolled with the circumstances. But mention bitter pit, and Grant’s disposition takes a turn all too familiar to fellow apple growers across the country.

For starters, she concedes there is probably no such thing as a completely bitter-pit-free year. Worse, that may be the only predictable trait of the physiological disorder, which is characterized by brown, sunken lesions on the apple’s skin and underlying spongy, brown tissue.

“Nobody really understands bitter pit. I can’t find a pattern yet,” Grant says. “One day somebody will figure this out, and their name will be in lights.”

What is common knowledge about bitter pit is that it involves, among many factors, nutritional imbalances, largely calcium deficiency. But other than that, for Grant and many of her peers, “it’s just a black hole of throwing calcium,” she says.

To help address Grant’s concerns and demystify bitter pit and calcium delivery, we reached out to experts from crop input companies.

Danica Kluth, TKI’s PNW Regional Agronomist, Crop Nutrition, finds Grant’s vexation both common and valid. “Bitter pit is unpredictable,” she says. “And even when growers feel like they have done everything correctly, it can still happen. Agronomists and researchers have helped narrow down contributing factors, but it is still somewhat of a mystery.”

Abe Isaak, Field Agronomy Manager with AgroLiquid, agrees. “Many times, out of frustration, we wonder if anyone understands our issue or problem,” he says. “Other tree fruit issues, such as disease and pests, are easy to diagnose and treat. When treating them, you spray a fungicide for a disease or a pesticide for a pest, and the problem remains under control. Figuring out the root cause of bitter pit, on the other hand, can be tricky.”

Fortunately, the industry’s knowledge of bitter pit has increased in recent years, according to Rick de Jong, Rovensa Next’s Canadian Regional Manager. “We are now aware that there are a multitude of related factors that can impact bitter pit severity in a given season,” he says.

Building a proactive strategy becomes the vital component, Kluth says. However, as Grant laments at her northwest Michigan operation, even the best-laid strategies are often clouded by uneven results. “It is so inconsistent!” Kluth says. “Neighboring blocks with similar programs can have drastically different levels of bitter pit. It is a system of a physiological imbalance, not just a single deficiency. This makes it harder to treat with a one-size fits all approach.”

Isaac concurs, saying, “We know that calcium deficiency, primarily in surface cells, is the most common cause of bitter pit, and we know what should work to prevent or cure the symptoms. What makes it more frustrating is that we often get mixed results from applications, and it can be difficult to repeat the same results in another field.”

“Confounding,” Greg Clarke, Senior Field Market Development Specialist with Valent USA, concludes. “Producers are adding more calcium and doing everything correctly in their nutrition and irrigation programs,” he says, “yet they are still ending up with high bitter pit some years.”

For more, click here to continue reading the full article as part of our special report on Plant Health.

In addition, check out the previous reports in Meister’s Global Insight Series covering a range of topics from Irrigation Innovations to Agricultural Technology.