Scab, one of the most common diseases in apples, is caused by a fungus called Venturia inequalis. The disease mainly develops in cool, rainy conditions in the spring, and is characterised by dark spots on the fruit and leaves.
Affected apples are extremely unattractive and as a result are difficult to sell. Furthermore, early leaf loss due to virus damage reduces the vitality of the trees.
For many years, organic farmers relied on copper, sulphur and lime to control apple scab. However, it was found that copper had a number of negative environmental impacts, and now use of copper-containing products on apples and other crops is being gradually phased out across the EU.
The aim of the EU-funded REPCO (Replacement of Copper Fungicides in Organic Production of Grapevine and Apple in Europe) is, as its name suggests, to find, develop and implement alternative methods for controlling scab in apples, as well as downy mildew in grapevines, which is also currently controlled using copper fungicides.
Researchers from the University of Wageningen in the Netherlands tested a number of substances in the laboratory and found that yucca extract protected the plant from infection by preventing the fungus from budding. The additive also had a curative effect until at least one day after the plant was infected by the fungus.
Field trials in orchards in the Netherlands and Denmark also showed the extract to be as effective as a low dose of copper at controlling scab.
The researchers' findings represent an important breakthrough for organic apple growers. Some countries have already banned the use of copper entirely, and organic apple farmers there are experiencing severe economic losses due to their inability to effectively control scab outbreaks.
The researchers have patented their discovery and hope the product will be on the market in a couple of years.
This is the latest in a series of breakthroughs designed to improve apple production. Researchers at New Zealand's fruit science company HortResearch for example recently announced that they will shortly complete the public release of the world's most extensive collection of apple DNA sequences.
The release comprises over 50,000 apple gene sequences - referred to by scientists as expressed sequence tags (ESTs). These are DNA sequences from active genes in the plant; genes that govern such characteristics as fruit colour and taste.