Abstract
Reducing levels of fruit set is often desirable in many European pear (Pyrus communis L.) cultivars. With a negative linear relationship between crop load and fruit size, crop load management early in the season minimises wastage of tree carbohydrate resources and provides maximum benefits in terms of fruit size and quality. There are several tools available for managing crop load including hand thinning, chemical thinning, photosynthetic inhibition through shading or application of chemicals, mechanical thinning and pruning. While hand thinning is the most accurate method of reducing excessive crop loads, there are some major drawbacks. With awareness that the early thinning offered by chemical thinning provides distinct advantages with regard to fruit size and other quality parameters, chemical thinning is gaining increasing acceptance in pear production. Some chemicals are used worldwide for thinning, but there are differences between countries and growing regions on recommended application timing and concentrations. The risks involved in chemical thinning can be mitigated by use of a structured approach, using a sequential spray program with both bloom and post-bloom thinners. Knowledge of conditions that impact the carbon balance of the tree and the ability to make use of carbon-deficit conditions are likely to improve the predictability of chemical thinning. Mechanical thinning has potential as a thinning tool, with advantages over chemical thinning in that it is environmentally friendly, can be used in organic production and is not weather dependent. Although artificial bud extinction has not been trialled on pears to date, it has been shown to be economically viable in apple. As it is a precision crop load management method that minimises tree resource wastage, it should be given serious consideration. As growers require large annual yields of high-quality fruit, the aim of this review was to examine current and potential crop load management methods for European pear cultivars and provide a portfolio of available options that can be integrated into a systematic approach for managing crop load.
Highlights
Pears (Pyrus sp.) are grown in most temperate regions worldwide, with European pear (Pyrus communis L.) predominating in Africa, Australia, Europe and North andSouth America
The need for managing crop load in European pears varies by cultivar and region, reducing levels of fruit set is desirable in many pear cultivars to optimise fruit size and quality
As hand thinning is normally performed after natural fruit drop, there is considerable wastage of the tree’s resources arising from the delay in achieving target fruit numbers, fruit are unable to attain their optimum size
Summary
Pears (Pyrus sp.) are grown in most temperate regions worldwide, with European pear (Pyrus communis L.) predominating in Africa, Australia, Europe and North and. Factors that reduce vigour, including rootstocks, lead to a change in partitioning of assimilates, nutrients and hormones between the various sinks within the scion tree and are likely to favour the production of floral primordia [3]; this often leads to increased fruit set and imbalanced crop loads, especially when combined with productive cultivars such as ‘Williams’ and ‘Conference’ [4]. These orchards require good management to ensure good fruit size. As pears flower earlier than apples, they are more at risk of spring frosts affecting fruit set [15], making growers cautious of thinning during the bloom period [3]
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