B.C. Experiences with 'Ambrosia' Maturity

During a recent meeting with the New Variety Development Council in Summerland, BC it was suggested that I share their experiences with 'Ambrosia' in BC with the apple growers in Ontario. As a result, Charlotte Leaming (with the Okanagan Tree Fruit Company field service) generously supplied me with an array of notes to create this article from.

Growers have the greatest influence on the eating quality of 'Ambrosia' apples out of storage by harvesting at optimal maturity. This will minimize firmness loss and disorder development during storage. In a 3-year study from 2001 to 2004, Dr. Sam Lau refined optimum harvest maturity and storage guidelines for 'Ambrosia'. On the 9-point starch chart that he developed, 'Ambrosia' should be harvested at:

• 2.5 to 3.5 for 5-6 months in CA
• 3.5 to 5.0 for 2-4 months in CA
• 5.0 to 6.0 for short-term storage and immediate consumption only 

Average starch movement is 1.5 points per week, although in warm years starch movement can be considerably quicker. The harvest window is shorter than many cultivars, normally lasting 7-10 days.

'Ambrosia' should be harvested based on the starch charts. Once sufficient starch clearing has occurred, all fruit down to the minimum colour requirements should be harvested. A second harvest may be made 4-7 days after the first. 'Ambrosia' may be harvested in one or at most, two picks.

According to Dr. Sam Lau, 'Ambrosia' has a 7-10 day harvest window if fruit harvest is initiated at a starch index of 2.5 (22% of the cross sectional areas clear of starch) on a 0-9 scale. For each additional day of harvest delay after the starch index has reached 2.5, the harvest window for a given block will be reduced by 1 day and the storage life reduced by 1 week or more (particularly in late picked fruit with starch index >5.0). Fruit destined for 4-5 month storage are best picked at a starch index of 2.5-4.0 (22-28% of cross sectional area clear of starch).

Although red-colour development occurs within a few weeks of harvest, it is not a good indicator of maturity. The amount and intensity of red colour depends on the nutritional status of the trees, as well as the day and night-time temperatures close to harvest.

Current colour requirements for 'Ambrosia' packing is 30% #4 red colour for Extra Fancy and 25% #2 red colour for Fancy. Often the first pick can take-off 80% of the crop, but most growers do not pick deep enough on the first harvest. Growers should pick right down to the minimum colour for Extra Fancy. However, do not wait until the background is yellow to harvest, as the fruit will be over-mature for storage. Background colour has more to do with nitrogen levels in the fruit than maturity and background colour usually changes in storage. 'Ambrosia' colour charts, developed by Rita Yastremski, are available to growers through the New Variety Development Council (BC) for $15.