Apple Fruit Disorders - Optimum Calcium Rate to Minimize Bitter Pit

Cultivars prone to corking and bitter pit should receive 9 to 11 lb of actual calcium per season.
Apple Fruit Disorders - Optimum Calcium Rate to Minimize Bitter Pit - Articles


Photo by M. Basedow

At the winter meetings I presented the concept of maximizing calcium applications. For many years we recommended using rates of calcium chloride of between 14 to 50 lb. These rates were determined after many years of research by Dr. George Greene since that was the cheapest, most effective material. The table below translates the recommended rates of calcium chloride into pounds of actual or elemental calcium needed in various situations that you might encounter. The minimum rate is 4 to 5 lb of calcium per acre per season. The standard rate for most orchards in the Mid-Atlantic is 6 to 8 lb. On cultivars, such as Honeycrisp and York Imperial, which are more susceptible to corking and bitter pit, the rate should be 9 to 11 lb and for enhanced storage life 12 to 14 lb is recommended.

In an informal survey of growers I learned that not many were using calcium chloride for a number of reasons. They were using a large range of products being sold by the agricultural suppliers. Further investigation showed that many were not applying enough equivalent product to meet the 14 to 50 lb rate of calcium chloride.

To help you decide on what alternatives to calcium chloride might work we developed two Excel spreadsheets to calculate how much of an alternative material would need to be applied to reach equivalent rates of calcium chloride. One sheet was set up for "determining optimum rate to minimize bitter pit." The other was set up to allow "for individual product comparisons." Lynn Kime took these two "calculator" sheets and made them into downloadable pdf files that you can use to run "what if" scenarios with the products of your choice. Using the two pdf files you can adjust your application of any calcium product you use to ensure an optimum level of actual calcium is applied.

The first sheet allows you to calculate the amount of actual calcium you would apply per application for a particular product. It has two sections--one for liquid products (top) and one for solid products (bottom). For liquid products you will need to determine the weight of a gallon of the product in pounds and enter that on the sheet. Second you will need to enter the rate in the appropriate box for quarts, pints or gallons per acre from the label. For solids scroll down further and enter the amount in pounds per acre. Divide the amount applied per spray into the pounds of actual calcium you want to apply per acre per season and you will know how many applications you will need to make.

The second pdf sheet lets you compare a number of different commercially available products to determine the number of applications needed, based on the labeled rate, to achieve the level of actual calcium you want to apply. Open the file and save the sheet to your computer. In the upper left hand corner there is a blue box where you enter the amount of actual calcium per acre over the season that you want to apply. Enter a value between 4 and 14. Find the product you want to use by scrolling down the alphabetical list of products to come to the one you want to use. Enter the average number of applications you make during the growing season in the green box in the center of the page for each different product and hit return. Based on the low and high rates listed on the product label the first two red-outlined boxes to the right will give the amount of actual calcium per acre that you are applying in the number of sprays you entered. The next two red-outlined boxes will show you how many applications of that product you need to make to achieve the rate of actual calcium you entered in the first blue box in left hand corner.

Rate Recommendations

Actual Ca lb/A/SeasonExpected Results
4 to 5This is the lowest rate that should be used. It will give some control of bitter pit and corking, will cause no leaf burning and will probably not enhance storage life of the fruit
6 to 8Should give good control of preharvest physiological disorders and probably should be the standard rate where these disorders are chronic problems. It will not cause any significant leaf injury and will probably not enhance fruit storage life.
9 to 11Should give excellent control of corking and bitter pit and should be the intermediate rate for PA. It may somewhat enhance fruit storage life and should result in almost no leaf injury
12 to 14The highest rate that should be used in PA and should give outstanding control of corking and bitter pit. It may result in some slight burning on the edge of the leaves but not until September or October. Rate may enhance storage life of the fruit