Prohexadion calcium:

• Shoot growth reduction by prohexadione-calcium (PC) (Kudos and Apogee) early in the season (at Pink) significantly reduces bitter pit incidence by 45-54%.
• PC applications at pink also reduce the incidence of blossom blight and subse­quent shoot blight.
• Considerations for applying PC:
  • Use at the rate of 6 oz/acre.
  • PC is not active at high pH levels: Use magnesium sulfate or water conditioner to lower the pH level.
  • PC should not be mixed with calcium or boron.
  • Adding a surfactant to the tank increases the efficiency of PC applications.
  • Use anti-foam agent if the surfactant is one that foams.
  • If the water source contains high levels of calcium carbonate (hard water), add ammonium sulfate (AMS).
  • Both Kudos and Apogee are labeled for use at pink in apples.

Pink Lady (top) and Gala (bottom) flower buds on April 8, 2019.

Calcium applications:

• Between 15-50 pound of calcium chloride should be added per acre per year to reduce bitter pit incidence. In other words, 2-8 pound/cover spray.
  • Calcium chloride should not be applied at temperatures above 85 ^o
  • Early season applications of calcium are more important than late-season applications.
  • Foliar applications of Ca nitrate are not recommended for Delicious and York. They might cause cork-spot like symptoms.
  • Soil applications of Ca are not efficient.
  • Ca nitrate contains 13.5% nitrogen and it might affect fruit coloration if nitrogen levels in the orchard are already high.
  • Calcium content in fruit is largely affected by crop load, vigor control, and nutrient management.
  • Fruits in the higher part of the canopy contain more Ca than those in the lower half of the tree.
  • Boron deficiency may reduce Ca movement in the tree.

Boron applications:
– Boron is essential for Ca movement and Boron deficiency may lead to Ca-deficiency disorders including bitter pit.

• 3-4 lb/acre of solubor can be applied at tight cluster or pink/white stages; 7-10 after petal fall or with the first cover spray.

Nitrogen applications:

• The annual amount of nitrogen for mature apple trees in high-density planting is about 50-80 lb/acre. If the soil has 3% organic matter, this alone can contribute 30-40 lb/acre of nitrogen.
• Foliar application of urea early in the season at 3 lb/acre (prior to bloom) or 5-6 lb/acre (at petal fall) is beneficial for fruit set, early fruit growth, and leaf development.