The Key To Bitter Pit in Apples? Unlock The Calcium
December 4, 2023 
Bitter pit symptoms present in apples.
Photo by Seth Elkington, Agro-K Corp.
On the subject of plant nutrition, no issue stirs apple growers like bitter pit and their ongoing quest to reduce the disease — particularly in ‘Honeycrisp’ — by maximizing calcium (Ca) uptake.
Crop nutrition suppliers have these tips to share.
Agro-K: The solution is not simply “more calcium,” International Business Development Manager Rick de Jong says. In turn, growers should avoid nutrient mixes that create antagonistic situations and take advantage of nutrient combinations that provide uptake and plant utilization synergies, he says.
Early-season zinc (Zn) and phosphorus (P) have significant roles in the development of the fruit’s vascular system, de Jong says.
“This vascular system represents the highway facilitating Ca movement in the developing fruit. The right time to get foliar applied Ca into the fruit,” de Jong says, “is during fruit cell division, which lasts from fruit set until roughly three to four weeks post-petal fall.”
Mid- and later-season foliar Ca applications help ensure the Ca needs of a tree are being met, which protects fruit Ca.
“When making foliar nutrient applications, make sure to use products that are designed for foliar use,” de Jong says. “It is easy to cover a leaf with a nutritional product, but it is much more difficult to get nutrients into the leaf. The most expensive fertilizer applied is the one that never penetrates the plant.”
Finally, de Jong says, growers should avoid significant potassium (K) applications during the fruit cell division window of opportunity, as K antagonizes the movement of Ca into the fruit during this time.
“Ensure that the trees are getting enough early-season manganese (Mn) to support K uptake regulation by the tree. As Mn levels drop, plants can begin to luxury feed on K, drawing in more K than what is needed, which antagonizes fruit Ca levels,” de Jong says. “Take advantage of the synergistic impact of boron (B) and Ca by applying them together early season, if needed by the crop. Simply by applying Ca and B together, one can increase the uptake of both nutrients by the crop.”
Verdesian Life Sciences: The company’s approach includes diligent soil and tissue sampling to monitor nutrition labels and ratios. It also attempts to determine if foliar applications of Ca and/or K help balance the apple with the Ca deficiency.
“The difficulty with Ca is getting that element into the plant — which ends up in the fruit — while at the same time not creating other nutritional imbalances. That’s the tricky part,” Technical Development Manager Larry Stauber says.
Verdesian’s Ca formulations can help in-season, at harvest, and postseason by mitigating the severity of bitter pit in apples, Stauber says. “A successful foliar program not only provides premiums for the grower at harvest but also in storage,” he adds.
Novozymes BioAg: There is no silver bullet for bitter pit, Technical Agronomist Jon Treloar says. The disease can be influenced by various factors, including weather conditions, tree health, and the specific growing environment.
“Regular monitoring and adjustment of your orchard management practices are key to managing this disorder effectively,” he says, citing soil testing, regular Ca sprays, proper soil pH, consistent watering, fruit thinning, fertilization monitoring and adjusting, pruning and canopy management, harvesting at the correct time, and storage conditions.
If necessary, Treloar says, growers should consider planting apple varieties that are less prone to bitter pit than ‘Honeycrisp’ if it continues to be a significant problem.
Crop Vitality/Tessenderlo Kerley Inc. (TKI): The application of a soluble Ca source through fertigation has been shown to reduce the incidence of bitter pit and improve overall fruit quality, Manager of Agronomy Zack Ogles says. Monthly applications of the company’s Ca thiosulfate (CaTs) at a rate of 5 to 10 gallons per acre can reduce bitter pit as well as provide essential sulfur (S), he adds.
ICL Growing Solutions: The company recommends that its four-in-one mineral fertilizer Polysulphate (14% K2O, 12.2% Ca, 3.6% Mg, and 19.2% S) be used as a foundation for Ca management as part of the spring-time soil application of granular NPK fertilizer blends. Although foliar application of Ca may still be included, the product will provide sustained root uptake of Ca throughout the season, allowing the apple tree to uptake and translocate Ca to the developing fruit, North American Agronomy Lead Jason Haegele says.
Microbial Science Laboratories: Ca is notorious for being locked up with P and other elements in the soil, according to Owner Kevin Johnson. The company’s Microbe Remedy Phos-Min product contains all microbes in a concentrated form to break apart locked up P, Ca, and other elements in the soil, making them all plant available. A new product, Outbreak, Leaf, Bud & Flowering Enhancer, is applied to leaves. It contains Ca and other ingredients that increase budding, flowering, and fruiting, as well as help prevent leaf diseases.
Agro-100 Global: Managing Partner Lorne Bienstock reminds growers to be patient and persistent in their efforts, as improvements may take time to manifest. He recommends various practices, including:
Maintaining consistent and well-regulated irrigation practices to ensure even distribution of water and nutrients to the apple trees. “Avoid excessive irrigation or uneven watering, which can lead to Ca uptake issues,” Bienstock says.
Properly prune and thin the trees to ensure that there’s sufficient light penetration and air circulation through the canopy. “This helps reduce humidity and minimize conditions conducive to bitter pit development,” he adds.
Regularly inspect trees for early signs of bitter pit and maintain detailed records of cultural practices, environmental conditions, and disease occurrences to identify patterns and trends.
Nutrien Ag Solutions: Steven Williams, Facility Manager at Nutrien’s Hendersonville, NC, location, monitors bitter pit in ‘Honeycrisp’ apples in the eastern U.S. via research from North Carolina State and Cornell universities as well as grower experiences in the field.
Williams says treatment starts with maintaining a soil pH in the 6.5 to 7 range while applying high Ca, lime, and gypsum. Growers should all soil nutrient levels and add as needed. Meanwhile, avoid excessive nitrogen (N) fertilizer as this tends to increase bitter pit.
Nutrisync (Loveland Products) calcium and boron should then be applied at petal fall every two weeks, Williams says. “Spray calcium chloride several times during the season as well,” he says. “After fruit set, start thinning with NAA (naphthaleneacetic) acid, such as Refine (Fine Americas).”
AgroLiquid: Foliar calcium is best applied early in the growth of the fruit, according to Agronomist Abe Isaak.
“When the apples are small – a dime to quarter size – the fruit will move with the foliage when the air blast sprayer goes down the row,” he says. “You have a much better chance of coverage on the apple than later in the season when the apple is heavy and harder to move.”
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