Rootstock Evaluation Should Not Only Measure Yield Efficiency but Also Potential Yield and Crop Value at the Optimum Projected Spacing

Authors: ROBINSON, TERENCE - Cornell University; Fazio, Gennaro

Submitted to: Acta Horticulturae
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/31/2022
Publication Date: 9/1/2022
Citation: Robinson, T.L., Fazio, G. 2022. Rootstock Evaluation Should Not Only Measure Yield Efficiency but Also Potential Yield and Crop Value at the Optimum Projected Spacing. Acta Horticulturae. 1346, 775-782. https://doi.org/10.17660/ActaHortic.2022.1346.99.
DOI: https://doi.org/10.17660/ActaHortic.2022.1346.99

Interpretive Summary: The choice of which apple rootstock to use in a new orchard has implications that go beyond tree size control, total yield and production efficiency. This manuscript makes the argument that when evaluating apple rootstocks in coordinated apple rootstock trials, the evaluation parameters should go beyond the traditional vigor and yield classification and include the optimum planting density of any given rootstock based on its experimental vigor potential and the portion of potentially cullable fruit that would not be eligible to enter the commercial stream. After making those adjustments, the economic differences in estimated crop value among rootstocks using the projected yield differences was very large, especially with high priced varieties like ‘Honeycrisp’ and could be as high as $250,000 per acre over 14 years. Thus, the practical decision of which rootstock to use for a new orchard can have very large economic consequences that often are not appreciated by apple growers.

Technical Abstract: Rootstock trials usually rank rootstocks based on yield efficiency calculated as cumulative yield per unit of trunk cross-sectional area. There is usually a positive correlation of dwarfing and yield efficiency. Using yield efficiency as the primary criteria of selecting superior rootstocks generally results in the most dwarfing rootstocks being judged superior to the more vigorous rootstocks. To better evaluate the commercial value of rootstocks we estimated the optimum planting density of any given rootstock based on its trunk cross-sectional area. We then calculated a projected cumulative yield per hectare at the optimum spacing. We then calculated a cumulative crop value. This effort has shown that some of the most dwarfing rootstocks would not produce the highest cumulative crop value even when planted at very high densities. The economic differences in estimated crop value among rootstocks using the projected yield differences was very large, especially with high priced varieties like ‘Honeycrisp’. The difference can be as high as $220,000 per ha over 8 years or $530,000 per ha over 14 years. Thus, the practical decision of which rootstock to use for a new orchard can have very large economic consequences that often are not appreciated by growers.