Calcium for Bitter Pit Control

The decision on whether to spray apple trees with calcium is not a simple one. Many factors need to be considered to allow you to realistically assess the probable benefits, and weigh these against the potential downside. The upside of calcium application is less bitter-pit. However, this result is not guaranteed, and it doesn't often eliminate the problem completely. The downside is earlier maturity in some cases with associated yield and size reduction as well as the potential for leaf-burn. So grab an apple and let's go through this. As it turns out, they're good for your brain.

Risk factors for bitter pit that should be considered

1. Variety Sensitivity - Honeycrisp and Northern Spy appear particularly susceptible. Delicious, Idared, Crispin, Cortland, and Empire are less sensitive but can suffer from bitter pit under the right conditions.
2. Orchard History - From past experience, you know how much of a problem bitter pit is in your orchards.
3. Nitrogen Status - The temptation to step up N application for bigger apples increases the risk of bitter pit. More N results in more growth, calcium uptake can't keep pace so the calcium that is there gets diluted to a lower concentration.
4. Heavy Pruning - Increases N content of the tree.
5. Light Crop Load/Excessive Thinning - results in larger apples and more susceptibility to bitter pit.
6. Young Trees - These tend to be growing fast, diluting the calcium in the tree and have lighter crop loads.
7. K and Mg Status - are positively charged ions just like calcium, and they compete for uptake. Higher levels of K and/or Mg result in less calcium uptake.
8. Boron (B) deficiency - B is involved in the process of moving calcium up the tree. Deficiency can be found by leaf analysis and corrected with foliar sprays.
9. Weather and Soil Moisture - Hot weather or drought stress shuts down transpiration which shuts down movement of calcium up the tree. Roots cannot pick up calcium from dry soil.

Precaution for Calcium Spraying

Ontario experience has shown that calcium spray advances maturity of McIntosh and Northern Spy. Use calcium only if bitter pit is expected for these varieties and avoid high use rates later in the season.

Calcium Sources

1. Calcium Chloride (77% flakes) is the cheapest form of calcium. However, it is the most likely to cause leaf burn. Application McIntosh, Golden Delicious or Idared varieties have shown excessive leaf burn and should be avoided.
2. Calcium Nitrate should not be used beyond the end of July unless foliar N is low. Otherwise reduced colour development and storage problems may arise. Application can cause fruit damage on Crispin and Golden Delicious and should be avoided.

Branded Calcium Sources are available and should be applied at rates that give an equivalent rate of elemental calcium to the above table. Some examples:

• This Ca, OligoCa 6 % calcium
• Liqui-Cal 8 % calcium
• CaB'y 10% calcium
• Stopit 12% calcium

The goal of calcium sprays is to increase the concentration of Ca in the fruit. For this to occur, the spray must be absorbed by the fruit. Apply sufficient volume to completely wet the fruit. For much more information, consult the OMAFRA Factsheet "Bitter Pit Control in Apples"

Learn more:

• An Apple A Day May Protect Against Brain Disease
• Bitter Pit Control, OMAFRA Factsheet Order No. 00-009

| Top of Page |