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Bitter Pit and Honey Crisp: How Much Calcium Are You Getting?

Reducing bitter pit in Honey Crisp and other sensitive apple cultivars continues to be a challenge. Effective bitter pit management requires integrating cultural, soil, water, and crop nutrition practices. Applying calcium (Ca) sprays every two weeks during the growing season, often beginning in mid-June, for a total of 4-8 applications is one management tool.

There are many calcium products available. The product used is not as important as the total amount of actual calcium applied over the season. To maximize the potential benefits up to a total of 12 kg actual calcium/ha per season is often required. This is usually applied in four or more sprays.

Regardless of which calcium product you may choose, it is important to know how much actual calcium the product selected provides over the season.

Determining how much calcium is applied in one season using a dry calcium product:

Calcium chloride (78% technical grade) has been shown to be cost effective in reducing bitter pit. It contains 27.8% calcium. It is applied at a rate of 5 kg/ha per application. In this example it is applied 8 times during the growing season.

(%calcium in product ÷ 100) X product application rate/ha X number of applications per season¹ = total amount of calcium applied per ha in one season

(27.8 ÷ 100) X 5 kg/ha X 8 = 11.1 kg

¹ Maximum applications from product label

Determining how much calcium is applied in one season using a liquid calcium product:

In this example, the product contains 6% calcium. It is applied at a rate of 6 L/ha per application. To determine the actual amount of calcium applied in a liquid formulation, you also need to know the product's container weight and its volume. Here the product weight is 24 kg and its volume is 20 L. It is also applied 8 times during the growing season.

(%calcium in product ÷ 100) X (Product container weight ÷ product container volume) X product application rate/ha X number of applications per season¹ = total amount of calcium applied per ha in one season

(6 ÷ 100) X (24kg ÷ 20 L) X 6 L/ha X 8 = 3.5 kg

¹ Maximum applications from product label

These simple calculations allow you to compare how close to the desired 12 kg actual calcium per ha per season each product applies. Deciding on which calcium product best suits your bitter pit management program also depends on how affectively it integrates with your other strategies. But it is important to know how much actual calcium you are applying over the season.

More information on managing bitter pit can be found in OMAFRA Factsheet, Bitter Pit Control in Apples, Order No. 00-009