Mike Basedow and Lailiang Cheng 

 In 2022, a team of Cornell researchers and extension agents once again evaluated peel sap nutrient analysis and the passive method for their ability to predict bitter pit in Honeycrisp across the state. In this short article, we’ll discuss some of our initial findings from the Champlain Valley following our 90 day post-harvest storage ratings we conducted late last week.  

Methods 

In this portion of the study, 30 blocks from orchards in Clinton and Essex counties were followed throughout the growing season. For each block, we collected fruit in early July when they weighed approximately 55-60g. Fruit were then peeled, and their peel sap nutrient concentrations were analyzed on campus.  From this, we were able to determine each blocks K/Ca and N/Ca ratio.   

Three weeks before harvest, we then collected 100 bitter pit free fruit from each of the 30 blocks. Fruit were stored at room temperature at a local packing house for three weeks, and were then rated for bitter pit incidence in accordance with the passive method protocol.  

Finally, at commercial harvest (9/15) we once again harvested an additional 100 bitter pit free fruit from each block. These fruit were conditioned at 50°F for one week, and were then stored at 38°F for 90 days. Following storage fruit were rated for bitter pit presence.  

Champlain Valley Bitter Pit Levels in 2022 after 90 Days Storage 

Compared to 2021, fruit appeared to be larger this year, and across the sites had higher rates of bitter pit (30 block average 43%) than in 2021 (30 block average 16%). While we cannot say with absolute certainty, we hypothesize the increased incidence of bitter pit is likely due in part to the amount of rainfall we received late in the growing season across northern NY. Rainfall likely kept the fruit growing large right up into harvest. At this point in the year, calcium movement into the fruit is very limited, while other nutrients like K continue to move into the fruit. This likely further throws off the K/Ca ratios, and increases bitter pit. Note that we also picked our storage fruit on the early side of Honeycrisp maturity, and expect apples from later picks may have less bitter pit coming out of storage.  

How did the prediction models perform?  

This year the peel sap K/Ca and N/Ca models did not perform as well as they had in 2021. Practically speaking, the K/Ca ratios predicted 12 low bitter pit risk blocks in 2022, 13 moderate risk blocks, and 5 high risk blocks. If we use 0-10% as low risk, 10-20% as medium risk, and 20%+ as high risk, our actual numbers after 90 days of storage this year were 2 low risk blocks, 3 medium risk blocks, and 25 high risk blocks.  

This year the K/Ca ratio explained approximately 28% of bitter pit variation after 90 days of storage in Champlain Valley fruit, and the N/Ca ratio explained about 8%.  In 2021, K/Ca ratio explained 42% of post storage bitter pit variation, and N/Ca explained 21%. This underprediction and the decreased relationship may be due to the amount of late season rain we had in the Champlain Valley this season.  

 

2022 regressions of peel sap K/Ca and N/Ca ratios to 90 day post storage bitter pit. This data shows some relation of K/Ca to bitter pit, and very little relation between N/Ca and bitter pit this year. 

 

2021 regressions of peel sap K/Ca and N/Ca ratios to 90 day post storage bitter pit. This data shows improved relationships of K/Ca and N/Ca ratios to 90 day post storage bitter pit compared to fruit in 2022.  

In general, the passive method also underpredicted bitter pit risk across Northern NY this season. The predicted percent bitter pit 30 block average was 21% this season, while the actual 30 block average of observed bitter pit after 90 days of storage was 43%. Again, this underprediction may be do the late season rains we received. However, the passive model performed relatively well in the regression analysis, explaining 58% of the variation in bitter pit we saw between blocks following 90 days of storage.  This is very similar to its performance in 2021, which also gave an R2=.58.  

Regressions of the passive bitter pit prediction method and bitter pit after 90 days of storage in 2022 (left) and 2021 (right). The passive method showed somewhat good correlation with the amount of bitter pit post storage.  

 

Current Takeaways 

These findings suggest to us that while not always a perfect predictor, the passive method can be a valuable tool in giving us an idea of the relative amount of bitter pit from block to block to assist in making some of your storage decisions.  While the peel sap predictors were not as strong of predictors this year as they were in 2021, we feel they still give us an early look at our potential bitter pit levels, and having this information in July allows us an opportunity to make management decisions for that block later in the season, such as increasing foliar calcium applications throughout the summer, and skipping ReTain and Harvista applications on blocks with a high K/Ca ratio. We feel using both of these tools in combination give us helpful information for managing bitter pit in our orchards (peel sap), and in making storage decisions at harvest (passive method).    

Future Work 

We hope to continue this work for an additional season across the state.  If you haven’t tried these methods before, but would like to in 2023, please reach out to me at mrb254@cornell.edu or 518-410-6823.