F.M. Maas, P.A.H. van der Steeg
To achieve target yields, crop regulation measures in ‘Conference’ pears may vary from year to year and may embrace measures to stimulate flower bud development and enhance fruit set, but often also chemical thinning of excess fruit. In ‘Conference’ the value of the crop at harvest strongly depends on the size distribution of the fruit. The aim is to harvest as many pears as possible with fruit diameters of 65 mm or more, since these sizes provide better economic returns than do smaller fruit. In years with ample flowering and good conditions for pollination, fruit set frequently becomes excessive and thinning is needed to realize the target crop load and the desired fruit size. Hand thinning is labor intensive and thus expensive. Therefore, chemical thinning is being examined as a cheaper alternative. Brevis, a new and specially formulated thinning agent containing metamitron, proved to an effective thinning agent. Depending on orchard conditions, desirable levels of thinning were obtained by the use of single or repeated applications of 175 to 350 mg/L metamitron at the 8 to 12 mm fruit diameter stage of development. Higher dosages were needed to thin well-pollinated ‘Conference’ trees compared to trees in orchards without pollinators. Thinning was also achieved by the use of benzyladenine (BA), tank mixes of BA and naphthalene acetic acid (NAA), and ethephon. Optimum thinning by BA was established at concentrations of 150 mg/L. Thinning efficacy of BA was increased by the addition of 5 to 10 mg/L NAA. The extent of thinning increased with the concentration of NAA in the tank mix. Ethephon applied at 12 to 14 mm fruit diameter also thinned ‘Conference’ pears, but was somewhat less effective than the combination of BA and NAA. The percentages of fruit having a diameter >65 mm were significantly increased up to 80 to 90% of the yield for those treatments that thinned the trees to the target fruit load of about 110 fruit per tree.
Maas, F.M. and van der Steeg, P.A.H. (2011). CROP LOAD REGULATION IN 'CONFERENCE' PEARS. Acta Hortic. 909, 367-379
DOI: 10.17660/ActaHortic.2011.909.41
BA, 6-benzyladenine, chemical thinning, ethephon, fruit size, metamitron, NAA, 1-naphthalene acetic acid, Pyrus communis

Acta Horticulturae