Science Into Practice - Thinning strategies

Hand thinning has consistently been the most reliable way to thin flowers or fruits in orchards. But to save costs, tree-fruit growers are in desperate need of reliable alternatives.

HDC project TF 215, which was led by Harriet Roberts of ADAS, reviewed alternative methods used around the world.

UK growers face similar challenges to those overseas although we have been more wary about using mechanical thinners, given that just 16 Darwin machines have been sold in the UK.

Trials throughout the world show very promising results and as we improve their use and investigate more about their long-term effects, such machines are likely to prove to be cost-effective options for our cooler climate.

In terms of chemicals, gaining approval for metamitron in the UK is an exciting prospect because it appears to be a less temperature-dependent fruitlet thinner than alternatives whose efficacy can be adversely affected by low temperatures following application.

When compared with hand thinning and no thinning, both mechanical and chemical thinning strategies can demonstrate both positive and negative effects on fruit quality. Improved fruit firmness and sugar content were identified in some papers from mechanically and chemically thinned fruit, suggesting that the method of thinning could influence storage potential.

Further work is required to clarify this and assess the effect of different thinning techniques on trees' long-term health.

The full grower summary for project TF 215 can be found on the HDC website at

Horticultural Development Company

For details on all HDC activity, visit

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