research update

Dealing with Draper drop

Study finds high calcium levels key to success in optimizing production. By Judie Steeves


avings could be more than a million dollars for Fraser Valley blueberry growers with discovery of how best to manage Draper blueberries to prevent fruit from dropping prematurely. Genetic and plant breeding researcher Eric Gerbrandt with Sky Blue Horticulture says it all has to do with the application of calcium, but both quantity and timing are critical to success. He just completed a two-year trial funded by the B.C. Blueberry Council and the Investment Agriculture Foundation with $38,500 through the Canada-B.C. Agri-Innovation Program, into premature fruit drop in the Draper variety, by the use of a foliar calcium spray.

Premature drop of Draper blueberries.

different plots, he began to work on a variety of quantities and timing, and found that those without a calcium application dropped 30 per cent of their fruit before harvest.

Eric Gerbrandt

With different applications, he got that figure down to five per cent and determined the interaction of calcium and nitrogen was causing the problem. Using a survey of soil, leaf and fruit samples, he replicated trials in three fields in Langley and Abbotsford in four blocks of 10 treatments each, and compared the high and low rate of calcium at three different stages in the season: 50 per cent bloom, middle of the season and late in the season.

He measured plant

responses and tested soil and leaves to determine the concentrations required for optimum effect.

Typically, there is a drop of as much as 25 per cent of the berries from Drapers just as the fruit is turning blue, ready to harvest, losing growers all their investment up to that point in fertilizers, cultivation and management of the bushes to the lost harvest. The problem occurs in northwest Washington State and B.C., but not in Oregon, Gerbrandt notes.

He wondered whether the drop was due to a calcium deficiency, such as causes blossom end rot in tomatoes and bitter pit in apples, and he determined that it was.

The next step was to work out when and how much calcium would need to be applied to prevent fruit drop. Using different applications in

20 British Columbia Berry Grower • Summer 2017

Foliar calcium applications turned out to be very effective at decreasing fruit

drop and improving fruit quality and quantity. Fruit drop was reduced to two per cent, saving thousands of pounds of fruit from losses on the ground. “It made me very happy to have done something which so clearly can help growers optimize production,” he comments.

Key to success is the use of high concentrations of calcium, Gerbrandt notes. Use of calcium at a rate greater than 1,000 parts per million is essential to success, he says.

He recommends growers talk to their field representatives or consultants regarding their spray program. Applications need to be early, from bloom onward, at seven to 10-day intervals, beginning in the early stages of fruit development. Three to four applications are probably sufficient, he figures.

Next he plans to investigate the genetic basis for fruit drop with a goal of reducing the incidence in breeding the next generation of varieties with Draper parents.

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