Chemical thinning of 'Conference' with metamitron (Brevis)

The acreage of pears in Belgium has grown steadily over the past 20 years and since 2008 it exceeds the acreage of apples. In 2015, 369 million kg of pears, of which 90% of the cultivar ‘Conference’, have been produced on 9,340 ha. With the production increase, the size of the pears is an increasingly important factor for the determination of the price. To obtain a higher average fruit weight, the number of fruits tree^-1 has to be optimized. Before the authorization of the chemical thinning agents 6-BA (Globaryll 100 and Exilis) and metamitron (Brevis) hand thinning was the only way to reduce the number of pears after an abundant fruit set. But because of high labour costs, chemical thinning is preferred. The result of the chemical thinning depends on temperature, tree vigour, pollination (the number of seeds), the difference in fruit size and the light intensity 14 to 30 days after full bloom. Mostly, the thinning effect of 6-BA (Exilis and Globaryll 100) with ‘Conference’ is too weak and ‘overthinning’ rarely occurs. Metamitron (Brevis), however, can give an excessive thinning, especially at higher dosages, when the treatment is repeated or after spring night frost. Therefore, our advice is to use 6-BA (Exilis or Globaryll 100) when only a mild thinning is intended. On trees with an abundant number of flower buds and ideal weather during bloom, one treatment with 1.1 to 1.5 kg ha^-1 Brevis (metamitron) is recommended. The optimal time for the application of Brevis is at an average fruitlet diameter of 8 to 12 mm on the 2-year-old-wood. A later application is possible, but the gain on average fruit weight is already compromised and results are more inconsistent. An earlier application is less effective.