Considerations for growers interested in production of the Ambrosia apple in Michigan

Michigan Tree Fruit Commission travel grant funds provide for the study of a potential variety for the Michigan apple industry at the 2018 IFTA Summer Tour.

Ambrosia apples and sign.
Photo by Amy-Irish Brown, MSU Extension.

Ambrosia has become one of the most widely planted apple varieties in British Columbia in the past decade. Discovered as a chance seedling in the early 1990s in the Similkameen Valley in British Columbia (BC), this variety has proven itself to be a valuable fresh market variety for the Canadian fruit industry. The 2018 IFTA summer tour provided the opportunity for closer examination by Extension personnel on the potential of this variety for production in Michigan, and for specific discussions with successful Ambrosia growers throughout the Okanagan valley in British Columbia.

After in-field study and discussion with experienced growers, we at Michigan State University Extension believe that the variety shows promise for Michigan tree fruit growers in the Fruit Ridge, Oceana-Mason, and Northwest regions due to its environmental requirements, harvest season and potential market niche. However, as with any variety a discussion of the horticultural requirements and additional considerations for this variety is important for prospective Michigan growers.

Harvest season and fruit characteristics

This variety ripens at or just before the typical timing of Jonagold. As fresh market growers look to phase out Jonagold and move to a more lucrative fresh market variety, Ambrosia may be an attractive option as a potential replacement for this harvest timing. Growers in British Columbia report that the natural harvest window is very short (roughly 10 days) if the fruit is not treated with PGR’s, so the usage of Harvista on the variety is highly recommended. Blocks that are not treated with Harvista are somewhat prone to rapid maturation and become overly ripe quickly. ReTain is not favored by the British Columbia apple industry on this variety due to reduction in color development that could occur.

The fruit has a square, symmetrical shape with pronounced lobes at the calyx end of the fruit like a Red Delicious. The apple typically has a low-acid, sweet flavor, and a firm, crunchy texture after up to a year in storage. Samples of the variety from last July during the tour still held their crunch and a solid flavor. It has an industry reputation in British Columbia as a good keeper.

The variety can struggle with excessive size, so thinning and crop adjustment during pruning must be handled with care. Growers in British Columbia report that while a few limited southeast Asian markets such as Vietnam are currently paying a premium for a jumbo-size Ambrosia, growers overwhelmingly aim to leave more fruit on the tree during thinning to keep size down.

Ambrosia is generally a blush-type apple, displaying yellow background with 50 percent or more pink-to-red when colored properly by the producer. Growers in British Columbia have consistently observed that coloring occurs late in the season and is heavily dependent on diurnal temperature variations. Successful Ambrosia growers consistently warned prospective growers throughout the tour that this variety is not for growers who struggle to color varieties like Honeycrisp due to excessive late summer heat and absence of cool early fall night temperatures. Generally growers in British Columbia feel that growers on sites that consistently get excellent color on Honeycrisp each season can feel good about their prospects of coloring Ambrosia successfully. For this reason, we believe that growers on the Fruit Ridge, Oceana-Mason, and Northwest regions are most likely to see relatively consistent success with color.

Horticultural considerations

Growers have experimented successfully in British Columbia with a variety of rootstocks including M9, NIC29, G41, and G11. Opinion of the best stock was dependent on site, farm soil type and historical issues with replant problems. However, British Columbian growers consistently noted that regardless of rootstock, the tree is not prone to producing long limbs, instead producing high numbers of spurs in a fashion reminiscent of varieties such as Red Delicious. For this reason, spacing between trees for variety on any of these rootstocks in high density systems is recommended to be two feet or less. Since the top 2/3 of the tree do not throw long enough limbs to fill trellis space at a 3+ foot spacing, tighter spacing is considered to be the most efficient and profitable system.

Most growers in British Columbia had the variety planted at 11-12 feet between rows, so Michigan growers could likely feel good about the decision to plant the variety at 12x2 or 11x2. Due to its tendency to form fruiting spurs over longer branches, this variety lends itself extremely well to 2-dimensional fruiting wall high density production. Growers strongly cautioned against trying to grow this variety as a semi-dwarf.

Site considerations

Growers in British Columbia feel that Ambrosia does well in any locations that can consistently color Honeycrisp. We observed it growing successfully in a variety of soil types including clay, sandy loam, and sand, assuming that the choice of rootstock was appropriate.

Diseases and disorders

Like other prominent fresh market varieties currently being planted around Michigan, Ambrosia is very susceptible to fire blight and requires a high caliber management plan during the key window of susceptibility in the spring. The variety is not scab resistant. Growers in British Columbia did not report serious issues with sunburn, bitterpit, lenticel breakdown/rot, russeting, storage rots, or internal browning.

Special thanks to the Michigan Tree Fruit Commission and all commodity groups who support the work of Michigan State University Extension.

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