March 31, 2008 By Dan Wooley
Doug Nichols, a field researcher
with the Nova Scotia Fruit Growers’ Association, and Harrison Wright,
an Atlantic Food and Horticulture Research Centre technician in
Kentville, N.S., have found all sorts of ways to grow bigger and better
Doug Nichols, a field researcher with the Nova Scotia Fruit Growers’ Association, and Harrison Wright, an Atlantic Food and Horticulture Research Centre technician in Kentville, N.S., have found all sorts of ways to grow bigger and better Honeycrisp apples.
The pair recently reviewed some of the techniques they have examined as a research team to help improve the colour and size of the Honeycrisp variety.
They believe a grower’s attention should be focused on four main areas of Honeycrisp management: establishment of the tree’s optimum crop load; control of its energy budget; limiting its canopy and spur wood; and adjustment of its blossom
Every apple tree’s crop load is based on its trunk cross-section area, also known as its TCSA. For high marketability, Wright recommends Honeycrisp trees be thinned to just three to six apples per square centimetre of the tree’s TCSA. At 15 to 20 apples per square centimetre, it is “cropped to death” and will produce only small apples of highly variable colour that are only suitable for juice.
Low load trees result in more soluble solids in their fruit “because (the tree) can put more into the apples,” he says. Trees with lower fruit loads also have greater apple firmness because the fruit will have much higher sugar and water content.
Tree foliage, through photosynthesis in one season, produces nutrients for storage in the tree for the next growing season. Heavy tree loads unbalance the tree’s energy budget, resulting in greater fruit mortality in the next season, notes Wright. By bringing seed to maturity, heavy tree loads waste energy as it moves into seed and fruit production, leaving less energy for other tree functions.
The grower can reduce tree energy loss by not allowing too much fruit to develop, explains Nichols. “You want to get into canopy development before moving into the fruiting stage.”
He recommends that up to three-quarters of the tree’s spur wood should be removed to achieve the optimum number of spurs and allow for new shoot development. Rigorous spur removal must be done to in order to maintain the Honeycrisp quality demanded by the market, Nichols insists, “It doesn’t come without cost. This is very tedious work.”
Honeycrisp is very light sensitive. But a grower can meet the fruit’s requirements for colour development by ensuring even light penetration through the tree’s canopy all the way to its bottom branches. “Without good light penetration in the canopy, you will sacrifice colour development,” says Nichols, adding, “You need to remove wood continuously to get the quality of apple you need.”
He recommends lateral regeneration by removing limbs to allow good light penetration through the tree canopy.
Thinning blossoms from 300 clusters on a tree to 50 clusters can help increase the tree’s fruit set from 37 to 77 per cent, explains Wright, by helping the tree conserve energy for a higher fruit set. He recommends early thinning to reduce the tree’s “biennial tendency” for vegetative growth, while improving apple quality. Therefore, he says hand thinning should begin in July and result in about 100 blossom clusters per tree. Once blossom clusters hit the 150 per tree mark, “you start sacrificing quality. You probably want one apple every seven to eight inches per tree limb,” Wright says, adding that those fruit need to be positioned far out on the tree’s limbs and well away from the bottom of the tree.
While hand blossom thinning had the most impact on Honeycrisp quality during Nichols’ and Wright’s trials, Nichols still recommends the application of three foliar calcium sprays in the spring, July and August, while avoiding excess nitrogen application.
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