Research by Dan Donahue at Cornell University reported that the timing of Prohexadione Calcium (PC) applications for bitter pit suppression is critical. Applications at the pink stage, at a rate of 6 ounces per acre, can suppress up to 50% of bitter pit incidence, but delaying application to normal thinning time does not reduce bitter pit. Here are some recommendations for the use of PC to suppress bitter pit:

1. Temperature Considerations for PC Application: Temperature plays a critical role in PC application and its effectiveness. PC relies on metabolic activity within the plant for uptake and metabolism. Therefore, temperatures below the mid-60s °F raise questions about application timing at the pink stage. Delay the application until temperatures are warm enough for up to eight hours post-application.

• Foliar Calcium and Boron Application with Apogee: It is not recommended to mix foliar calcium with PC in tank mixes because PC effectiveness decreases in high pH solutions, which would also be the case when using hard water with a high content of calcium carbonate. In the latter case, you can add ammonium sulfate to reduce water pH and increase PC effectiveness. It is also not recommended to mix it with Boron as interactions could also reduce PC effectiveness.

• Enhance the performance of PC by adding a surfactant that will assure good wetting and coverage.

• Avoid PC application at pink for bitter pit suppression in young-bearing orchards that have not filled their allotted space, as it can lead to excessive vegetative growth reduction. Instead, use other foliar calcium programs that will promote fruit quality without affecting tree growth.

This article was posted in Apples and tagged Amaya Atucha, Apples, Bitter pit, bitter pit control, Prohexadione Calcium.