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Is the Maturity of Honeycrisp Affected by Calcium Sprays?

Good question – one definitely worthy of an exploratory type trial. Based on past experiences with calcium sprays on other varieties like “McIntosh” and “Northern Spy”, we know that an aggressive regime of calcium sprays can result in some wild and unforeseen changes in predictable maturity.

At the time in the late 90’s, these experiments and trials were being looked at because there was the general consensus that if you added foliar sprays of calcium to a cultivar like McIntosh you would delay the maturity and make the apple harder by more cementing of cell structure from the added calcium. What actually happened was the exact opposite, as the crop matured earlier and the fruit were generally softer with advanced maturity.

This appears to be related to ethylene generation in the canopy of treated trees. Back in the late 90’s when we were trying to figure out why growers applying up to 14 lbs of actual calcium per acre (if they could get it on) saw much of the crop on the ground long before it could be retrieved for storage and sale. We found ethylene at 8x’s the threshold in the canopy and fruit of trees treated with an aggressive spray program of calcium chloride, compared to untreated trees. This pushed the crop maturity about 10 days ahead of the untreated checks. We found that the more calcium chloride you got on, the worse the maturity problem got.

It is not so bad getting earlier maturity if you’re ready for it. One might hypothesize that it could potentially be used as a marketing tool on a small scale to get some fruit ready for immediate sale ahead of the bulk of the crop. The down side of course is that you loose on volume of production, as the last 10 days fruit are on the tree is normally the final quarter of an inch of growth and 20% of the crop volume. Harvesting fruit like McIntosh with a maturity of 5 or 6 on the starch index does not make for any long term storage potential.

To make a long story short, since the late 90’s we have invested huge sums of money into the cultivar Honeycrisp in Ontario and we have shown that we can grow some of the finest looking fruit of this cultivar in North America.

Honeycrisp is a variety that is subject to bitter pit. We have installed a small experiment to see if repeated sprays of a few recommended calcium source materials for bitter pit, have any effect on maturity of this exciting and relatively new cultivar.