Use of thinners can increase the fruit size of blueberries in an evergreen system

In Australia, small and sour fruit can be a problem for growers of southern highbush blueberry (Vaccinium corymbosum L.) during the early season. A field experiment examined the impact of hand thinning and the foliar treatments, urea, ammonium thiosulphate (ATS), benzyladenine (BA) and ATS/BA combination on blueberry cultivar 'OB1' fruit quality for an entire season. Treatments were applied over four weeks from the first harvest. Urea (5%) and ATS (0.78%) were effective at desiccating open flowers. However, BA (0.015%) failed to thin fruit, applied alone or following ATS. Fruit size (berry weight and diameter), increased towards the end of the season without compromising yield for hand thinning, ATS, BA and ATS/BA. However, thinning had no effect on the concentration of total sugars or acids. Foliar urea, although an effective desiccant, had little effect on fruit size, and despite its use to reduce leaf senescence in autumn, it had no effect on the leaf canopy area. Future research should evaluate earlier applications of ATS and BA for increasing fruit size early in the season when fruit weight and diameter are most limited.