Prohexadione calcium to reduce bitter pit incidence: 

– Shoot growth reduction by prohexadione calcium (PC) early in the season (at Pink) can significantly reduce bitter pit incidence in ‘Honeycrisp’ apples.

– PC applications at pink also reduce the incidence of shoot/fire blight.

• Use at the rate of 6 oz/acre.
  • PC should not be mixed with calcium or boron.
  • Adding a non-ionic surfactant (e.g., Regulaid or LI700) to the tank increases the efficiency of PC applications. 
  • If the water source contains high levels of calcium carbonate (hard water), add spray-grad ammonium sulfate (AMS) to the spray tank at a rate of (1 lb AMS to 1 lb PC) or according to the product label.
  • Don’t spray if rain is expected within 8h of application.
  • Both Kudos and Apogee are PC products labeled for use at the pink stage.

Calcium applications:

– Between 15-50 lb of calcium chloride (CaCl2) should be added per acre per year to reduce bitter pit incidence. In other words, 2-8 pound/cover spray.

• Early season applications of calcium (starting @Pink) are more critical than late-season applications.
  • Foliar applications of Ca nitrate are not recommended for Delicious and York. They might cause cork-spot-like symptoms. 
  • Avoid CaCl₂ applications at temperatures above 75 ^oF or under slow drying conditions (e.g., early morning) as this might cause damage to the foliage, especially in sensitive apple cultivars (e.g., Idared and Golden Delicious).  
  • Soil applications of Ca are not efficient.
  • Boron deficiency may reduce Ca movement in the tree.

Boron applications:

– Boron is an essential element for flower development and fruit set, and boron deficiency can negatively affect yield and fruit size.

– Boron is also crucial for Ca movement, and Boron deficiency may lead to Ca-deficiency disorders, including bitter pit.  

• Maintenance rate: 0.5-1 lb of Boron/acre (2.5 – 5 lb of Solubor/acre)
  • Apply at Pink stage, tank mixed with calcium chloride. 
    • OR, 7-10 after petal fall; or with the first cover spray.
  • Research at WA state showed a significant positive relationship between splitting in Gala and fruit boron content. So, it is recommended to use the lowest rate of boron with Gala.

Urea applications:

Foliar applications of urea at bloom (3 lb/100 gal) and at petal fall and early cover sprays (5-6 lb/100 gal) can promote cell division, especially for Gala. These applications are particularly important when king blooms, which usually give the largest fruit, are lost to frost.