Commercial Production of Honeycrisp Apples in Ontario
Table of Contents
Honeycrisp, also known as Minnesota #1711R, originated at the University of Minnesota and was introduced in 1991. Although originally its parents were thought to be Macoun and Honeygold1, genetic testing has demonstrated this to be incorrect and that one parent is known to be Keepsake (Bedford, Personal communication). Few new apple cultivars have created as much excitement or challenge as Honeycrisp. Consumer and market enthusiasm, and grower interest has driven the acceptance of this cultivar much more rapidly than most2, 3 (Figure 1).
Figure 1. Honeycrisp apples are inherently large, with a unique and distinctly crisp texture. When sufficiently thinned, it takes very few apples to fill smaller containers.
Honeycrisp has an upright, spreading tree growth habit, with low vigour, spurry fruit development and high precocity. Its vigour depends on the soil type and rootstock and therefore can be variable based on environment and cultural management, but overall can be categorized as a weak-growing tree. Honeycrisp blooms mid to late in the flowering season when compared to other cultivars and appears to be pollinated by any diploid in the same season such as Cortland, Empire, Redfree, and Fuji4. Honeycrisp in turn produces viable pollen. The cultivar is cold hardy, reportedly withstanding temperatures as low as 34°C. For propagation purposes, it is necessary that nurseries obtain virus free wood since the original Honeycrisp tree contained stem-pitting virus.
Figure 2. Honeycrisp is a bi-colour apple that develops more red in cooler regions.
The Honeycrisp fruit is large ranging from 79 cm (2¾3½) diameter, especially when trees are young. It has an oblate shape, and medium stem length. The skin is thin and not prone to russet. It is a bi-colour apple that develops more red in cooler regions (ranges from 5090%) (Figure 2). The flesh is cream coloured, and like Cortland, does not oxidize or brown readily when the apple is sliced. The fruit has a unique, distinctively crisp texture which, combined with the thin skin, adds to its high palatability. It maintains this texture in storage. Although not a highly flavourful apple, it has a good balance of sugars and acids and tends to be more acidic in cooler climates. Harvesting Honeycrisp at optimum maturity can be challenging, as the regular maturity indicators such as ethylene, starch, soluble solids, and firmness are not always good indicators of the best time to pick. Research has shown that starch is the best indicator5. A 15% soluble solids is required before fruit is harvested6. Experience suggests that in the absence of testing for ethylene, surface blush colour is the best indicator of maturity. The following maturity guidelines have been developed: starch of 5.05.5 using a 6 pt scale; fruit pressure of 6.87.7 kg (1517 lbs); and 15% soluble solids.
Honeycrisp typically matures around mid September in Simcoe, Ontario, although multiple picks are necessary because the fruit does not mature uniformly. Fruit qualities including firmness, taste, and storage potential can be compromised by late harvest dates, and therefore harvest should not be delayed in order to achieve greater red colour.
Honeycrisp has been found to be very susceptible to preharvest drop especially in warmer growing regions or seasons. ReTain helps to decrease this problem (Figure 3).
Figure 3. Pre-harvest fruid drop of Honeycrisp can be problematic in some years.
Honeycrisp does not develop red colour uniformly. Colour variability can be explained by environmental stresses, virus expression, or genetic variation. Red colour development can be achieved by vigour control, crop load management, tree training to improve light penetration, and appropriate dormant and summer pruning. Informing consumers that a redder apple does not necessarily mean a better eating experience may also be important for successful marketing.
If harvested too late, Honeycrisp occasionally develops fermentation products such as acetalaldehyde and ethyl acetate. This causes a disagreeable flavour that develops after late harvest, which can worsen in storage. The onset of this pungent taste is difficult to predict and there are no external visual symptoms on the fruit to indicate its presence. Harvesting fruit at optimum maturity is the best method to prevent its occurrence.
Stem punctures and bruising are problems because of its thin skin, and can account for significant losses7,8. These stem punctures can increase the development of blue mould decay Penicillium expansum9. Stem punctures can be avoided by extremely careful handling or clipping the stems at harvest and controlling blue mould by good sanitation practices to prevent contamination of punctured apples.
Figure 4. Heavily cropped Honeycrisp trees produce poorly coloured, low quality fruit. Judicial thinning is essential.
Since the trees can start to bear fruit very quickly after the establishment period, thinning is very important for the production of marketable apples. Honeycrisp is easily thinned at the 1012 mm diameter stage of fruitlet growth using 2.55 ppm NAA for young bearing trees and a combination of 2.5 ppm NAA and 0.5 L Sevin XLR/100 L for heavily set mature trees10, 11. Over-cropped trees in excess of 8 fruits per cm trunk diameter (3.5 cm circumference) produce poor coloured fruit with inferior storage potential (Figure 4).
A target crop load of approximately 6 fruits/cm2 trunk area (measured approximately 1520 cm above the bud union) is recommended to produce the highest quality fruit and to avoid biennial bearing. The final crop load must be reached early in the season to achieve maximum benefit. For example, a typical 4-year Honeycrisp tree with a 12.5 cm trunk circumference (C), would have a trunk cross section area of approximately 12.4 cm2 [Area= (C x C) / (4 x 3.14)] and would ideally have no more than 62 apples per tree (Figure 5). However, fruit from over-thinned trees can be excessively large resulting in a net yield reduction and fruit, which are prone to bitter pit, senescent breakdown, rot, and soft scald. When hand thinning to final crop load, many growers have found that the removal of the largest fruitlets results in the most desirable fruit size distribution at harvest. For further information on chemical thinning please refer to the current issue of Publication 360, Fruit Production Recommendations12. Honeycrisp has bien-nial bearing traits even when trees are young. Thinning can help to establish annual flowering and therefore minimize this tendency.
Figure 5. Relationship between tree cross sectional area and number of fruit required per tree to maintain an 'ideal' crop load.
Honeycrisp is a low vigour cultivar and therefore a semi-dwarfing rootstock of M.26 or greater vigour is recommended. Honeycrisp on M.9 EMLA is not recommended, however reports from Michigan indicate that more vigorous clones of M.9 (such as M.9 RN29, Pajam 1 or Pajam 2) may be better suited than the M.9 NAKB 337. For growers with established plantings on M.9 EMLA, mounding soil around the base of the tree may improve vigour. Honeycrisp wood is brittle and therefore graft unions can be broken easily which has been particularly prevalent on M.26 (Figure 6). MM.106 has been used as an alternative for M.26 to avoid the bud union breakage13.
Honeycrisp is prone to several diseases and storage disorders making its culture and production potentially problematic for growers. However, these are manageable if dealt with properly and in a timely fashion. One positive attribute of Honeycrisp is that it is highly resistant to venturia sp. (apple scab) but not completely immune. Apart from silver leaf and fire blight, most concerns are of a postharvest nature. Fireblight tends to only be a problem when trees are growing over vigorously. Honeycrisp is also susceptible to cedar apple rust, rots such as black rot (Botryosphaeria sp.) (Figure 7) and Penicillium decay (Penicillium sp.), and highly susceptible to powdery mildew (Podosphaera leucotricha)14. Mummified fruitlets that fail to drop after fruit set are a likely source for this inoculum. The symptoms of powdery mildew, manifested by netting on the fruit surface, are also common in some orchards. This netting on the skin of the fruit can lead to a drastic reduction in marketable yield if not well managed (Figure 8).
Figure 6. Breakage at the graft union with M.26 rootstock has been observed in Ontario. Adequate tree support is recommended to avoid this problem.
Figure 7. Honeycrisp is very prone to storage disorders, including storage rots. Preharvest fungicidal treatment is highly recommended for extended storage.
Figure 8. Characteristic netting of Honeycrisp caused by mildew.
Another uniqueness of this cultivar is that it commonly develops a leaf complex indicated by interveinal chlorosis and leaf blotchiness not very dissimilar to a nutrient disorder (Figure 9). It is not known what causes these symptoms, or whether it is of any physiological consequence to the tree or fruit. However, indications thus far suggest that it is not environmentally based because it is found wherever Honeycrisp is grown. The leaf complex symptoms appear on extension shoot leaves early, worsen throughout the growing season and persist until leaf drop when leaves often become much browner in comparison with other cultivars.
Figure 9. Interveinal chlorosis and leaf blotchiness are common leaf characteristic of light-cropping Honeycrisp trees.
Its presence is more prevalent on trees with lighter crops and trees with less vigour. Although the symptoms resemble potato leafhopper damage, a nutrient defic-iency, or the presence of a virus, these are unlikely to be the primary cause. Some have suggested that the symptoms may be a result of excessive starch accum-ulation in the chloroplasts of leaves, which impairs the movement of starch from leaves to other parts of the plant such as fruits or roots. Regardless of the cause, orchardists growing Honeycrisp will soon discover these symptoms and might initially be quite con-cerned. Growers can be assured that this phenomenon is common and does not appear to affect tree performance.
Honeycrisp has a long storage potential of 67 months in common cold storage. Controlled atmospheric storage is not recommended at this time because of the high incidence of storage disorders. Research has shown it is best to store the fruit at 2.5°C3.0°C to decrease the incidence of post-harvest disorders such as soft scald and low temperature breakdown. Honeycrisp has excellent firmness and texture retention in storage, however, other quality charac-teristics such as soluble solids, water content, acidity, and flavour, can decline over time in storage.
One strategy that has been investigated to reduce soft scald is to temporarily hold the fruit for one week at 10°C and then reduce the temperature to 2°C3°C for long-term storage. Fruit however are more prone to decay, loss in flavour, and development of bitter pit. Therefore, using this approach would, in part, require adequate fruit calcium levels prior to long-term storage. The benefits of this strategy, however, have not been observed in studies in Ontario to date and therefore must be considered on a trial basis.
Honeycrisp fruits are prone to calcium related disorders such as bitter pit and cork spot (Figure 10). Trees that are over-thinned produce very large apples, which have a greater tendency to develop bitter pit. Furthermore, apples harvested early and stored in warm temperatures are more prone to bitter pit15. Trees with excessive growth often produce fruit with lower calcium concentrations because there is competition for calcium between the fruit and the tree. Environmental conditions such as fluctuations in soil moisture also play a role. Using calcium sprays16 and avoiding excessive nitrogen fertilization can help to control the development of these disorders. Since Honeycrisp is predisposed to bitter pit, especially in long-term air and CA storage, calcium, sprays are highly recommended. More information on the control of bitter pit control can be found in OMAFRA Factsheet Bitter Pit Control in Apples, Order Number 00-009.
Figure 10. Calcium sprays are recommended to prevent bitter pit.
Soft Scald, which is the development of brown lesions on the skin17, develops in storage if the fruit was harvested too late and stored at too low a temperature (Figure 11). Avoid the development of soft scald by harvesting at the recommended harvest date and storing at higher temperatures (above 1°C). Research in New York has suggested18, 19 that to reduce scald an effective conditioning pre-storage treatment is to keep fruit at 10°C for a week prior to going into cold storage. Due to the slow softening characteristics of Honeycrisp, there is minimal concern of it loosing its firmness. However, this method is recommended for storage periods less than 2 months. If used, the pre-conditioning method may increase the probability of the fruit developing bitter pit, and therefore a calcium spray program should be used before harvest.
Low temperature breakdown (soggy breakdown) is an internal disorder that causes soft, brown, spongy tissue to develop within the fruit cortex. It is caused by high crop loads, a late harvest, excessively cold storage temp-erature, and can be induced by climatic conditions during the growing season. Harvesting fruit at the recommended time and storing them at warmer temperatures (³ 3°C) can help remedy this disorder. More information on the low temperature breakdown can be found elsewhere20, 21
Figure 11. Soft scald develops in storage on over mature fruit or when stored at low temperatures.
Honeycrisp is protected under the U.S. Plant Patent Act (Plant Patent No. 7197). It may be propagated only by licensed parties. Firms or individuals desiring to propagate and sell trees of Honeycrisp must apply for a license from the University of Minnesota, Office of Patents and Licensing, Suite 201, 1100 Washington Ave. S., Minneapolis, MN 55415-1226. A list of licensed nurseries is available from the Department of Horticultural Science, Fruit Breeding Program, University of Minnesota, St. Paul, MN 55108.
This Factsheet was written by Dr. John A. Cline, Assistant Professor, Ontario Agriculture College, University of Guelph, Department of Plant Agriculture, Simcoe Campus, and John Gardner, Apple Specialist, Crop Technology, OMAFRA, London. This Factsheet was reviewed by Dr. Jennifer DeEll, Fresh Market Quality Program Lead, Crop Technology, OMAFRA, Simcoe.
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