News

Predicting Potential for Bitter Pit Incidence in Honeycrisp Apples

Bitter pit is known to vary based upon cultivar and season.

Updated:

July 25, 2019

Collecting calyx end peel sample for test to predict potential for bitter pit on Honeycrisp. Photo: T. Baugher, Penn State

Skip to the beginning of the images gallery

Rich Marini and Tara Baugher conducted a study a few years ago to try to determine if they could predict bitter pit with a preharvest nutrient sampling of the fruit peel. After the three year study, they were able to develop a predictive model based on peel nutrient analysis combined with average shoot growth length.

Three weeks before the anticipated harvest, select 20 trees in a block of Honeycrisp and collect three fruit from each of those twenty trees. Fruit should be similar in size from trees that have a similar representative crop load. At the same time or earlier in the week, determine the average shoot growth of the 20 trees by recording the length of 5 typical terminal shoots from around the tree. Select current year's shoots with moderate branch angles, avoiding strong vertical shoots or weak shoots hanging below horizontal.

Scrub the apples in tap water to remove any pesticide or calcium spray residues. Using a potato peeler remove 1 cm wide strips of peel from around the circumference at the calyx end of the fruit. Be careful to avoid removing apple flesh with the peel. Combine the peel tissue from the 60 apples, place on a tray with a sheet of parchment paper and dry in your oven at 180^oF overnight. Send the tissue samples to the Penn State Agricultural Analytical Lab in a standard plant analysis kit.

The graph below can be used to plot the average shoot growth versus the N:Ca foliar analysis ratio to determine the potential percent bitter pit from the block. The three lines represent different average shoot lengths that you might measure. The bottom line represents the average shoot length of 5 inches, the next one up represents 15 inches, and the top line represents 25 inches. You can use the graph to interpolate different shoot lengths and N/Ca ratios across the x-axis.