HomeCider ResearchCrop Load Recommendations for Cider Cultivars

Crop Load Recommendations for Cider Cultivars

Now that most (if not all) cider varieties have set fruit, we’re sharing highlights from some recently published research on crop load management for cider apple orchards, and some recommendations for hand-thinning.

From spring 2016 to 2019, the Peck Lab collaborated with CCE’s Lake Ontario Fruit Team on a project to increase the reliability and profitability of growing European hard cider apple cultivars in New York. Funded by the New York Apple Research Development Program (ARDP), this project compared the effects of different crop loads that were obtained by hand-thinning on bloom, multi-year bearing patterns, and fruit and juice quality for seven of the most widely planted European cider cultivars, as well as assessing appropriate harvest timing for these seven varieties. The research was carried out in a tall-spindle orchard in Orleans County. In addition to the three-year crop load experiment, a second study researched the effects of midsummer plant growth regulator (PGR) sprays (meaning they were applied to initiate flower bud development and not for thinning) on return bloom and multi-year bearing patterns in the same seven cultivars, as well more established trees of two of those seven cultivars at the Cornell research orchards in Lansing, NY. David Zakalik, technician and MS student, spearheaded these experiments.

In these experiments, we identified a target crop load of ~9 fruit/TCSA as being a target crop load for cider apple cultivars. In addition, we found that each cultivar had a different maximum supportable crop load, above which there was no return bloom. For the more annual-bearing ‘Chisel Jersey’ and ‘Dabinett’, trees could bear up to ~30 fruit/TCSA and still have some return bloom. Highly biennial cultivars ‘Geneva Tremlett’s Bitter’ and ‘Binet Rouge’, on the other hand, had no return bloom when cropped above ~15–20 fruit/TCSA.

In a 2021–2022 experiment, PhD student Shanthanu Krishnakumar examined the effects of different crop loads on yield, tannins, and return bloom in ‘Binet Rouge’ and ‘Porter’s Perfection’. Dr. Krishnakumar found that a crop load of ~10 fruit/TCSA optimized acceptable yield while also promoting sufficient return bloom. These varieties, in a tall-spindle system on G.11 rootstock, had no return bloom above ~20 fruit/TCSA.

Based on these findings, we recommend a target crop load of ~8–12 fruit/TCSA, in a tall-spindle production system to optimize cumulative yield, annual bearing, and juice quality. Though this is a higher crop load than recommendations for fresh-market cultivars, this is well below the range of crop densities observed in cider orchards without thinning. Partial budgeting analysis found that thinning to 9 fruit/TCSA was most likely to result in improved profitability for a grower selling fruit at the farm gate.

What does this target crop density look like for trees of different ages and sizes? For tall spindle trees on a dwarfing rootstock like B.9, in their fourth or fifth leaf, this translates to 50–100 fruit per tree. However, for trees on a more vigorous semi-dwarf rootstock like MM.106, in their fourth leaf, this translates to 400–500 fruit per tree.

Overcropping led to a “diminishing returns” effect: as crop density got up toward 20 or more fruit/TCSA, fruit got smaller and more bland, ultimately resulting in higher hand-harvest costs per pound (more apples to pick) and inferior juice quality. Left unchecked, we saw some cider cultivars set crop loads of almost 50 fruit/TCSA!

Thinning in the high-crop “on” year was highly effective at promoting return bloom, while thinning in the low-crop “off” year was not necessarily worthwhile. Before considering hand or chemical thinning, growers should assess fruit set in their cider orchard. When hand-thinning, it’s important to have your crew reduce each fruit cluster to one or two fruitlets, and space fruit evenly throughout the tree canopy.

Zakalik also conducted several dozen interviews with commercial grower-cidermakers about high-tannin apple supply and how it’s affected by biennial bearing, which turned into an industry survey with almost 200 responses from the US and Canada. After being written up in Zakalik’s MS Thesis, data from these experiments and the survey have since been published as three journal papers and one extension article (links at bottom.)

Now that we’ve identified a range of target crop loads, a new grad student is working on identifying chemical thinning programs for cider apple orchards.

Other Highlights:

  • English cultivars ‘Chisel Jersey,’ ‘Dabinett,’ and ‘Harry Masters Jersey’ were found to be most annual-bearing and most cumulatively productive, as well as most responsive to hand-thinning.
  • French cultivar ‘Michelin’ did not quite live up to its reputation as being annual-bearing or highly productive, while English subacid bittersweet ‘Brown Snout’ was fairly responsive to thinning and bore more consistently than expected from previous descriptions. ‘Binet Rouge’ and ‘Geneva Tremlett’ were found to be highly biennial, and only somewhat responsive to thinning.
  • Midsummer (non-thinning) sprays of NAA and Ethephon to promote return bloom did not work at the rates applied in these experiments, for any of the seven cultivars studied.
  • Crop load affected ripeness differently from cultivar to cultivar, though a broad trend was observed: ripeness (as measured by starch index) is advanced at very low (0–10 fruit/TCSA) and very high (≥30 fruit/TCSA) crop densities, but delayed at moderate (~20 fruit/TCSA) crop densities.
  • All measures of juice quality correlated negatively with crop density. When taken together with cumulative yield effects, overcropping can result in inferior tannin production per acre, as well as sugar content (Brix), acidity, and YAN.
  • Of the many high-tannin cider cultivars being grown in the U.S. and Canada, a dozen stood out as being most frequently mentioned by survey respondents. Of these, the reliable, annual-bearing ‘Dabinett’ and notoriously finicky, highly biennial ‘Kingston Black’ were top of the list. All seven cultivars in our experiments (see above) made the list, as well as ‘Porter’s Perfection,’ Ellis Bitter,’ and ‘Bulmer Norman’.
  • There is far more demand among cidermakers for high-tannin cider cultivars than the current supply can meet. The leading reason given for not using these cultivars was lack of availability. However, for most cideries, high-tannin fruit only constituted 10% or less of their total raw material.
  • Biennial bearing was cited as a supply-chain challenge for ~85% of growers, but only 16% of non-growers who buy in fruit from elsewhere.
How to calculate TCSA: To calculate TCSA (in square centimeters), take two measures of trunk diameter, at 30 cm above the graft union, roughly at right angles to each other. Then, using the area formula for a circle, divide the average of those two diameters in half to get the radius. Square the radius and multiply by Pi (π, or roughly 3.14). Once you have the TCSA value, simply multiply by your target crop density (somewhere between 8 and 12) to get the target number of fruit per tree. For example, if your average trunk diameter is 3.5 cm, the radius is 1.75 cm, so TCSA will be 3.14 × (1.75 × 1.75) = 9.6 sq cm. If your target crop load is 10 fruit/TCSA, then you’ll want (9.6 × 10) = 96 fruit on the tree.

Publications:

Cider Research, Crop load management