I attended the Eastern New York Fruit & Vegetable Conference February 22-23, 2023 in Albany NY. Hosted by the Cornell Cooperative Extension (CCE) Eastern New York Commercial Horticulture Program (ENYCHP). A day and a half of tree fruit talks, mostly featuring speakers from Cornell University and on many pest management (insect & disease) and production (horticulture) management issues. Check out my @jmcextman Twitter hashtag #ENYFVC for a bunch of picts and comment on their presentations.
One presentation worth bringing to you here was by Dan Donahue, tree fruit specialist with CCE's ENYCHP. Dan has always been quite inventive, so his talk was excerpts from his 'Honeycrisp Playbook,' a series of specific recommendations to mitigate bitter pit risk when growing Honeycrisp apples. So without further adieu, here is Dan's most recent and comprehensive 'Playbook' (in bold) with some comments by yours truly (in italics)...
Avoid replant sites - yea, Honeycrisp are tough enough to grow as it is, give them a break and grow on virgin ground and/or follow BMP's for replant sites (fumigation, cover-cropping, etc.).
Soil pH should be adjusted to about 7.0 - start a little high on pH with addition of lime to bring pH close to 7, that lime has calcium in it (don't use dolomitic-high mag limestone), and that slightly higher pH than the normal recommendation of 5.9 to 6.5 will enhance nutrient availability.
Use 30% less ground potassium (K) than other varieties - K is antagonistic to calcium uptake and movement in the plant, don't ignore the need to have some K (as dictated by soil/foliar nutrient tests), just don't use as much as you might, say with Gala?
Moderate nitrogen (N), shoot for 2.2% in the leaf analysis, no foliar N - high nitrogen = high bitter pit, enough said? Feed the roots N using calcium nitrate as dictated by leaf analysis, just err on the short side vs. lots of N.
Use B.9 or B.10 rootstocks, avoid Geneva rootstocks - pretty straight forward, M.9 rootstocks fall somewhere between B.'s and G.'s in bitter pit prevalence. B.10 is a bit more vigorous than B.9. Friends don't let friends plant Honeycrisp on G.41. Good tree spacing for Honeycrisp on B.9 are app. 2.5 feet between trees by 10-11 feet between rows. A bit more in Dan's study Bitter Pit Response to Rootstock and Region in Eastern New York State.
No apple crop in 2nd leaf - yup, grow your trees (with moderate nitrogen!) for years 1-3 in the orchard. Apples off young trees will be bitter pit prone anyways. Do de-fruit them when young, only start cropping when they are as tall and wide as you want, as they will stop growing (much) when they start fruiting.
Light to moderate tree vigor, pruning - a "calm" tree is what you want to mitigate bitter pit risk. Use thinning (vs. heading) cuts as much as possible while pruning.
Avoid precision pruning to a bud load < 2.5 buds per target crop load - yea, leave more buds than you might otherwise with say, Gala? You don't want to fall too far short of your target crop load in the end. Good insurance here. But I might go down to 2 buds per target crop load 😎.
Avoid aggressive, early crop reduction, aggravates bitter pit - normally we recommend thinning early and often. Not so much here, but there is a fine line. More below...
Prohexadione-calcium (Apogee/Kudos) at pink, do not apply post-bloom - Dan's work that has been field tested indicates Prohex-Cal applied post boom results in more bitter pit than when it is applied at pink. And actually, that pink application gives pretty effective growth control too. More here from Dan. And his own words "I recommend avoiding conventionally-timed Prohex if at all possible."
10 ppm NAA at bloom, avoid bloom thinning with ATS or lime sulfur - that NAA at bloom nudges the thinning start (but not aggressively) and also promote return bloom (well, at least it is a start). Bloom thinning with caustic thinners typically and aggressively thins early (what did he say above?) and leaves the king bloom typically, especially when using the Pollen Tube Growth Model. King bloom = larger apples = more bitter pit? Maybe, maybe not, this may not always be true. But you might get away with using caustic bloom thinners with B.9/10 rootstocks? If bloom thinning with caustics, you should be using the pollen tube growth model.
Calcium (Ca) at petal fall, continue through 5 weekly applications - I'd be using the formulated liquid calciun products (Sysstem-Cal, etc.) at this timing and then switch to calcium chloride mid-summer until harvest? More here from Dan.
Target chemical thinning at 8-12 mm stage - is this all starting to come together? Besides, particularly when following the carbohydrate model to determine rate and timing of chemical thinner applications, this is when THE most effective chemical thinning often happens, at 8-12 mm. Still, NAA 10 ppm at bloom! And don't forget to use the apple carbohydrate thinning model when chemical thinning at this time.
Hand thin to target fruit load at 35 days post-bloom - Honeycrisp initiates flower bud development early, as soon as 30 days after bloom. Too many apples on the trees thereafter will inhibit flower bud formation = biennial bearing. Get it? So hand thin Honeycrisp first!
3 sprays NAA at 5 ppm - that's 2 oz. per 100 gallons dilute tree row volume per acre, beginning no later 30 days post-bloom, then 45, then 60 -- for return bloom enhancement AND research has shown that the auxin factor of NAA reduces bitter pit. I recommend 2 oz. per acre, period. Some return bloom recommendations use ethephon, might be OK in addition to those NAA sprays.
Limit irrigation (deficit?) late June through harvest - yup, you don't need to be blowing those Honeycrisp apples up and diluting calcium (and promoting calcium sink shoot growth) = more bitter pit risk. More on deficit irrigation of Honeycrisp (where practicable LOL) here from Washington State University.
Use EMR model or passive bitter pit prediction protocol on M.9 rootstocks destined for long term storage - No need to test B.9 or Geneva rootstocks as they will have less or more bitter pit respectively Dan says. If you want to know more, here is the reference for EMR (Environment, Minerals, Rootstock): Daniel J. Donahue, Gemma Reig, Michael Rutzke, Anna Wallis, Michael Basedow, Sarah E. Elone. 2021. A Predictive Model for Malus × pumila Borkh c.v. ‘Honeycrisp’ to Reduce Storage Risk in Eastern New York State, U.S.A. Acta Horticulturae 1314. Proceedings of the International Symposium on Precision Management of Orchards and Vineyards, October 2019. https://doi.org/10.17660/ActaHortic.2021.1314.51 And, a bit more about the passive bitter pit prediction model here: https://www.goodfruit.com/to-predict-bitter-pit-let-it-sit/
Weigh pros/cons of using ReTain/Harvista sprays, may increase bitter pit - bitter pit risk increases with earlier harvested apples, might increase with later harvested apples, but not really sure here? Apples will get bigger = more bitter pit? There is a sweet spot for less bitter pit with intermediate harvest dates? Just something to keep in mind when using these harvest management tools.
M.9 rootstock, third pick for long term storage = less storage bitter pit - has shown to be the case for that third pick, might represent optiumum maturity?
That is the most current Honeycrisp Playbook (for mitigating bitter pit risk) according to Dan Donahue. But hey, check out It's the Calcium Stupid, some recommendations from the recently deceased Jeff Alicandro/agri.assistance, RIP Jeff.
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