Joe Nicholson of New York with a Rubinola tree that shows symptoms of sulfur intolerance.
Britain has only about a dozen serious commercial organic growers, estimates Dr. Jerry Cross, who heads the entomology and plant pathology team at East Malling Research.
And East Malling Research is one of them.
The research station has been downsized over the years, in terms of faculty, but it still has more than 500 acres of land. Some of the ground is used to produce crops to generate income for research. Almost 30 acres of organic apples have been planted over the last few years.
Cross showed members of the International Fruit Tree Association, who visited East Malling this summer, an 11-acre organic apple block planted in 2006.
“The first thing is to choose the right variety for organic apple growing,” he said.
The apple varieties most popular with U.K. consumers, such as Gala, Braeburn, and Jazz, for example, are susceptible to scab, so East Malling Research worked with two of the country’s major supermarkets, Sainsbury’s and Waitrose, to find out which disease-resistant varieties would likely be acceptable to consumers.
Of a hundred varieties listed initially, about five were selected as possibilities. The 2006 planting includes two from the Czech apple breeding program, Rajka and Rubinola, along with the German apple Ceeval, which also goes by the name Early Windsor or Alkmene.
Because scab resistance in those varieties is based on a single gene and is easily overcome by the scab organism, fungicides are applied to the orchard starting with a couple of sprays of copper at a low rate in early spring. After that, micronized sulfur is applied twice a month, starting at a rate of 5 kilos of sulfur in 1,000 liters of water per hectare (equivalent to about 5 pounds in 100 gallons per acre) and at reduced rates later in the season. Lime sulfur is not registered in the United Kingdom. Cross said the Rubinola trees are “sulfur shy” and showed signs of phytotoxicity.
Because of the United Kingdom’s cool, wet climate, conventional growers typically spray for scab every 7 to 10 days, which can add up to 15 to 18 applications per season.
Fireblight is not a major concern on apples, he said, perhaps because the weather conditions are not quite right. Antibiotics cannot be used in Europe, so growers avoid growing highly susceptible varieties, such as Egremont Russet.
The East Malling organic block produced its first, very small crop last year, in its fifth leaf. Production was affected by a very cool spring in 2010, but Cross said it is not a high-yielding system compared with modern intensive orchards. The trees, which are on Malling 9 rootstocks, are spaced 6 feet apart in the rows and rows are 11.5 feet apart. Tree density is 632 per acre.
This year, the United Kingdom had its warmest spring in 30 years, and the trees had relatively good crops. Cross noted, however, that the trees appear to be low on nitrogen, although 300 kilos per hectare of organic fertilizer with 8 percent nitrogen is applied annually, which is the equivalent of about 55 pounds per acre. A mix of grass and clover was grown on the ground for two to three years before the orchard was planted.
One of the main insect pests is rosy apple aphid, whose winged forms move from apple trees to nearby plantain weeds in the summer. Female aphids return to trees in the fall, followed shortly by males, and lay eggs on the tree after mating. Cross said that’s the time of year when they’re vulnerable to sprays, and pyrethrin applied in early October can greatly reduce the number of rosy apple aphids on the tree the following spring. Mating disruption is used for codling moth control.
No organic herbicides are available in the United Kingdom, Cross said, so weeds are controlled by tilling. East Malling uses a cultivator from Italy that has a blade on one side that undercuts the soil surface. With 11.5 feet between rows, there are 1.5 miles of rows per acre that need to be treated on each side, and the top speed for the cultivator is just over one mile per hour. This makes it a time- and fuel-consuming process, he said, and it needs to be done four to six times per season.