Half-baked Research 2021: Part 3 - In Search of the Optimum Honeycrisp Bitter Pit Reduction "Diet!"

 Honeycrisp is arguably the poster child for bitter pit. (With the exception of Cortland, but who would want to grow those anyways? LOL.) Bitter pit reduces packout of saleable fresh fruit significantly in some years, up to 50%. And you can put otherwise good looking (no bitter pit) Honeycrisp in storage and then  when pulled out of storage a couple months later you go home crying.

Much has been researched and written on Honeycrisp bitter pit management (reduction), however, the problem is nowhere near totally solved. Nutrients in the skin and flesh of Honeycrisp apples – particularly nitrogen, calcium, and potassium – may play an important role, but there are many other factors including growing season weather, crop load, tree vigor, etc., those are all players too. Read more in "It's the calcium stupid!"

But nutrition was the factor fully “looked at” but not really fully “evaluated” in 2021. By “looked at” I mean multiple leaf and fruit nutrient analyses using different analysis vendors, including industry and University testing labs. Let me outline what these were, and then attempt to make some sense of the results and how it might relate to bitter pit incidence. But I’ll tell you up front, Honeycrisp exhibited quite a bit of bitter pit starting pre-harvest in 2021, part of which I blame on a very wet summer and very large apples. All samples were collected from the UMass Orchard in Belchertown, MA, and I don’t consider our nutrition program specifically targeting BP all that much. So let’s see what tissue samples I/we collected and then what nutrient analyses results might have told us?

First, how/what/where tissue (and fruit) samples were collected and sent for analyses:

• Agro-K (Minneapolis, MN) has been promoting their leaf SAP analyses to existing and potential customers. Leaf samples – from older and younger leaves individually on terminal growth, enough leaves to fill a one quart zip-loc bag, and without petioles – are collected in the morning and shipped overnight (via FEDEX) to a lab in the Netherlands (NovaCrop). There were three collection dates for Honeycrisp: 15-June, 19-July, and 10-August. Oh, leaves were collected off Honeycrisp on G.11 rootstock, which has been problematic for bitter pit in the past. 
• Peel SAP analysis by the Cornell Nutrient Lab and Lailiang Cheng’s lab at Cornell AgriTech in Geneva, NY. Honeycrisp fruit samples (about 30 apples, off the same trees on G.11, and I also did G.41 to compare) were collected in early July when the fruits were 50 to 60 grams. The apples were peeled and the peels frozen prior to delivery to Cornell for the analysis. (Thanks to Mike Basedow for meeting me in the Hudson Valley and ultimately getting those frozen samples to Geneva.) I received the results back in mid-August, which included Ca, K, Mg, N (all ppm), and K/Ca, (K+Mg)/Ca and N/Ca ratios.
• Dan Donahue’s Environment Minerals Rootstock (EMR) bitter pit analysis out of Cornell’s Hudson Valley Commercial Hort Program. Honeycrisp fruits (app. 12, off both the G.11 and G.41 rootstocks) were collected in early August, peeled, and the peels sent off to Dan to forward to the Cornell Nutritional Analysis Lab in Ithaca. Results were back by mid-September and included the % of apples expected to have bitter pit developing in a month or two of cold storage.
• Various fruit and tissue samples were also sent off to two independent labs, Waypoint Analytical and SoilTech NW Ag Testing Services (analyses by Brookside Labs). Waypoint is open to anyone but SoilTech only to consultants by invitation. Basic mineral analyses with recommendations were performed, I will try to summarize the results below.

So here we go in an attempt to summarize the results of all the samples submitted to the various labs for analyses. And some snapshots of what the results looked like from each testing service.

Leaf SAP analysis – indicated there were generally few problems. The SAP analyses are quite comprehensive, including a listing of 24 line items, some not normally included in nutrient analysis, such as Total Sugars, pH, sodium, cobalt, and nitrogen in 4 forms (ammonium, nitrate, N in nitrate, and Total Nitrogen). Most nutrients were in the optimum range, with these exceptions: Fe (iron) was consistently low (is that a problem?); nitrate nitrogen and boron were high; and total sugars were high (indicates the plant is really cranking?) Remember, samples were collected over three dates and from old and new leaves on the shoots. Verdict out on this one, but over time might be very useful in quickly remedying problems or indicating you are doing a good job with nutrient management. Below in Figure 1 is a snapshot of the NovaCrop result but here is a full report if you want to see it.

Figure 1 - Portion of NovaCrop SAP analysis result

Peel SAP Analysis – courtesy of Cornell (thanks Terence Robinson and Lailiang Cheng), interesting and disheartening result when you see RED (as below in Figure 2) in the cells. RED usually means bad things compared to GREEN and YELLOW doesn’t it? But not too surprising, and probably a good analysis that I would buy based on field observation. And it aligned with the EMR results next…

Figure 2 - Peel SAP Analysis interpretation courtesy of Terence Robinson and Lailian Cheng

Environment Minerals Rootstock (EMR) – similar to Peel SAP Analysis, a bitter pit buffet. Suggests nearly a third (for G.41 at least, one out of 5 apples for G.11, bad enough) of the Honeycrisp will come out of storage with some bitter pit as seen in Figure 3. Not good. Nor did I verify that result unfortunately. Hence half-baked.

Figure 3 - Dan Donahue's (Cornell) EMR bitter pit prediction

Waypoint Analytical is my latest go-to for leaf analysis with the apparent demise of University soils and tissue testing labs? Waypoint provides a quick turn-around of results including a nice graphical output (Figure 4). For this years Honeycrisp/G.11 leaf analysis, well, it looked pretty good overall. The only nutrient judged deficient by Waypoint was Potassium. But I’d like to see Nitrogen trending towards the Low side, while Calcium would be on the high Sufficient side. See the whole PLANT ANALYSIS here.

Figure 4 - Portion of Waypoint analytical tissue (leaf) analysis output

And finally, SoilTech NW, which was a whole fruit analysis. SoilTech NW is a testing service by invite only as I mentioned, I have been using it in a collaboration with a managed apple variety. I really like their output, and they have developed their own set of desired nutrient ranges based on their database of samples over many years. The result here kind of mirrors the Waypoint leaf analysis, mostly in Nitrogen being high and Calcium low (Figure 5). Magnesium is kind of high too. All things being equal, Magnesium and Potassium are antagonistic to Calcium uptake, and with high Nitrogen it’s not a good outlook for bitter pit. Or do I mean it’s a good outlook for bitter pit, and a not so good outlook for storage potential as can be seen here in the complete results.

Figue 5 - Graphical interpretation of SoilTech NW fruit nutrient analysis

So, all things considered, I/we could have done better when managing nutrients in Honeycrisp for reduced bitter pit in 2021. There’s always next year, but remember there are many other factors affecting bitter pit incidence in Honeycrisp, primarily tree vigor (overly vigorous, excessive pruning), cropload (lighter with bigger fruit means more bitter pit), tree age (younger trees more susceptible), and high nitrogen/low calcium ratios. And in the Northeast, it was generally a high bitter pit year, the wet growing season (large apples and diluted calcium content) likely being the primary reason. But there is always room for improvement in nutrient management, and doing leaf and fruit nutrient analyses no matter which lab you use is necessary information to improve your orchard bitter pit reduction diet.