Research Matters - Fruit thinning in apple trees

Apple growers sometimes have to use fruit-thinning agents to stop their trees producing too many small fruit.

However, some of the established agents are now being phased out because they are thought to adversely affect human health.

In the experiments described here, 12-year-old 'Gold Rush' apple trees growing in North Carolina, USA, were sprayed with 1-naphthaleneacetic acid (NAA - 5mg per litre) when the fruit were 10mm in diameter. Once the spray had dried, uniform spurs from treated and untreated trees were removed and sprayed with solutions containing 0, 50, 100 or 200mg per litre of 1-aminocyclopropane carboxylic acid (ACC). These same treatments were applied in the following year.

The ACC is converted into ethylene by plant tissues and ethylene production was highest the day after treatment. The highest concentration of ACC produced the most ethylene and also considerably reduced the number of fruit set in both years. One disadvantage of using such a high concentration was that it caused some yellowing of leaves.

When NAA was applied alone, it too reduced fruit set but not by as much as ACC. When both sprays were applied to the same spur, their effects were usually additive. As NAA had little impact on leaf yellowing, one future approach might be to spray ACC in combination with NAA.

Dr Ken Cockshull, Associate Fellow, Warwick Crop Centre, University of Warwick

Effects of 1-Aminocyclopropane Carboxylic Acid on the Rate of Ethylene Release from Detached Fruiting Spurs & on Fruit Abscission in Apple by McArtney (2011). Journal of Horticultural Science & Biotechnology 86 (6): 640-644. The authors' abstract of their manuscript can be seen in full at

Have you registered with us yet?

Register now to enjoy more articles and free email bulletins

Sign up now
Already registered?
Sign in

Before commenting please read our rules for commenting on articles.

If you see a comment you find offensive, you can flag it as inappropriate. In the top right-hand corner of an individual comment, you will see 'flag as inappropriate'. Clicking this prompts us to review the comment. For further information see our rules for commenting on articles.

comments powered by Disqus

Read These Next

What challenges and opportunities lie in store for tomato growers?

What challenges and opportunities lie in store for tomato growers?

The British Tomato Growers Association (TGA) conference today (21 September) heard a range of perspectives on what changes lie in store for the sector and how to anticipate them.

Buoyant demand for UK apples but frost and labour remain concerns

Buoyant demand for UK apples but frost and labour remain concerns

As the British apple season begins, English Apples & Pears (EAP) is warning that growers will feel the effects of both a late frost in spring and also constrained labour supply.

Tomorrow's tractors

Tomorrow's tractors

These machines have advanced rapidly over recent years but what does the future hold? Sally Drury looks ahead.

Follow us on:
  • Facebook
  • LinkedIn
  • Twitter
  • Google +
Horticulture Jobs
More Horticulture Jobs

Pest & Disease Tracker bulletin 

The latest pest and disease alerts, how to treat them, plus EAMU updates, sent direct to your inbox.

Sign up here

Professor Geoffrey Dixon

GreenGene International chair Geoff Dixon on the business of fresh produce production

Read Professor Geoffrey Dixon