Affecting the Maturity of ‘Honeycrisp’ Using Calcium Chloride Sprays for Bitterpit Control

‘Honeycrisp’ apples are typically harvested during the middle of September in Southwestern Ontario. This cultivar is considered to be a bicolour apple and growers usually harvest this variety using multiple picks starting in mid September. ‘Honeycrisp’ requires adequate thinning to achieve optimal fruit quality. Colour can be considered as a very important trigger in determining readiness. Long-term storage of ‘Honeycrisp’, as with other apple cultivars, depends on relative starch degradation during the ripening process. Fruit quality can be compromised by late harvest dates. Waiting for more colour may mean a lower quality product.

Because of its inherent tendency to bitterpit on younger trees, growers customarily treat ‘Honeycrisp’ with calcium sprays.

A small controlled experiment was done during the 2006 growing season to determine if ‘Honeycrisp’ trees treated with calcium chloride sprays from two commonly used materials would influence maturity and starch degradation in the time period leading up to the typical first pick dates for this cultivar in Southern Ontario.

A replicated and randomized experiment was conducted using single tree sub-plots and comparing an aggressive treatment regime of calcium sprays starting when the fruit were golf ball size until late August for a total of five sprays. Sprays were applied using a handgun to achieve adequate wetting of fruit surfaces and canopy. Fruit from treated trees were compared to untreated check trees and to the growers’ own treatment. The grower applied a total of 7 lb/ac actual calcium over six sprays. While the experimental treatments delivered 13 lb actual calcium per acre based on the use of dilute spray applications to individual trees at the equivalent of 1000 l/ha of spray solution.

Fruit samples were collected on September 7^th well after the first few apples had started to drop from treated trees in the experiment. Apples were sectioned and tested with a standard prepared mix containing iodine in order to determine how far starch degradation had progressed in treated fruit compared to untreated checks and the growers’ own treatment regime. Fruit of trees treated with calcium sprays exhibited an advanced maturity when compared to the untreated check trees. Treated trees in the experiment produced a maturity similar to the grower managed trees which had also been sprayed with calcium to manage potential bitterpit problems.

The attached photo (Figure 1) shows the control or untreated check at the top left and the two treatments in the experiment to the right of the check, with the grower managed fruit samples at the bottom centre.

Figure 1. Control treatment is at the top left. The other two spray treatments are to the right of the control. The grower’s own treatment is at the bottom centre.