Belgian horticulturist Tom Deckers discusses the pruning strategy for a four-leader system. Many pear-growing systems put too much energy into production of shoots, he said. In this system, fruit develops close to the leaders.

Belgian horticulturist Tom Deckers discusses the pruning strategy for a four-leader system. Many pear-growing systems put too much energy into production of shoots, he said. In this system, fruit develops close to the leaders.

Geraldine Warner

A four-leader system is generating early and high yields of ­Conference pears in the orchard of Jan van der Velpen and his brother in Bierbeek, Belgium.

The system requires well-feathered nursery trees with at least six laterals so that the four best branches can be selected after planting as the future leaders, which are supported by individual ­bamboo poles. Their trees are on Quince Adams or Quince C rootstocks.

Two leaders are trained to each side of a V trellis. With more than 1,200 trees per acre, that means there are 4,800 production units per acre. “That’s one of the reasons why the productivity of this type of system is very high,” said Dr. Tom Deckers, pomologist at the Pcfruit research ­center in Belgium.

Trees on this system can produce 10 bins per acre in the second leaf and 25 to 30 bins per acre in the second leaf, reaching 50 to 60 bins at maturity. “The time is out when we wait seven to eight years after ­planting for the trees to start to crop,” Deckers said.

The vigor of the trees is divided between the four leaders. Deckers said vigor is more difficult to control when trees have only two leaders or are on a V system with trees leaning alternately to either side.

Van der Velpen’s plantings are irrigated immediately after bloom. Around 35 pounds of nitrogen per acre are applied in the spring, and 18 pounds per month are applied through fertigation during the growing season, making a total of approximately 90 pounds per acre for the year. About 22 pounds per acre of potassium nitrate are also applied. The additional nitrate helps assure the green fruit color that export markets prefer, ­Deckers said.

Fireblight

Fruit is exported to Germany and other northern European countries. Russia has become an important market. Belgian growers recently began exporting to China, though they’re not finding it easy. Fireblight is found in Belgium, but not China, so export fruit must come from a fireblight-free zone, which is verified through annual orchard inspections. Any orchard where fireblight is found can no longer export to China.

Deckers said the main control for fireblight is to cut out infected wood and burn it, as antibiotics are not approved in Europe. Infections arise mainly from secondary bloom, rarely from primary bloom, so it’s recommended that growers remove secondary bloom by hand. The fungicide Aliette (aluminum salts) is sometimes used to reduce tree susceptibility. Conference, Europe’s most common pear variety, is not particularly susceptible to fireblight, though Concorde, which van der Velpen uses as a pollenizer, is very susceptible.

The ideal size for Conference pears in European markets is 65 to 70 millimeters (2.6 to 2.8 inches) in diameter. Pears as small as 55 mm (2.2 inches) used to be profitable, but nowadays, even with a good variety, orchards growing small pears can lose money, Deckers said. “Good fruit size is essential in the whole business.”

Growers are looking at mechanical blossom thinning to reduce their labor costs for thinning. Deckers said the Darwin mechanical thinner causes too much damage during bloom, but might be a possibility before bloom.