Containing the spread of spotted wing drosophila (SWD)

Scrupulous hygiene and housekeeping across the farm are very important to contain the spread of SWD. Discarding fruits with SWD on open compost heaps or shallow burial must be avoided, as this enables SWD to reproduce, feed and overwinter (females in reproductive diapause).

The aim is to minimise favourable environmental conditions and materials that can protect and provide resources which will increase the reproductive rate of SWD. 

It is essential to:

• Dispose of waste fruit and materials with SWD
• Destroy them to prevent and control the spread of SWD
• Remove unmarketable fruits on the crop
• Remove damaged and fallen fruits as they are a source of SWD
• Remove other damaged crops and waste fruit (e.g. tomatoes, grapes, apples, pears) as these also provide ideal breeding grounds

Containment and correct disposal of waste are also essential in minimising the impact. There are several effective options which growers can consider for disposing of waste fruit:

• Freezing (IQF)
• Cooking/juicing/pureeing
• Drying
• Anaerobic digestion
• Enclosure to reduce oxygen

Within Objective 2 of research project SF 145, scientists at NIAB EMR have assessed the effects of anaerobic conditions on waste fruit (strawberry and plum). Waste fruit with larvae was contained in 500-litre plastic pallet bins, filled to within 10 cm of the surface. Black pallet wrap was laid across the surface of the bin and wrapped down the outside surface. The wrap must then be held down by the lid, sealing the fruit in the bin. See images below, demonstrating this along with the fermenting fruit under the polythene.

Once the bins are sealed, rapid depletion of oxygen occurs leading to anaerobic fermentation of the fruit, which results in the death of the larvae within 48 hours.

During normal seasonal conditions, the start temperature of non-cold stored fruit waste is usually between 14–25°C and does not rise significantly during the anaerobic treatment. However, the ambient temperatures must be warm enough to achieve this within the time period. Longer storage times may be needed at temperatures below 14°C.

Following fermentation the fruit waste separated into two layers: 90% consisting of underlying liquid and a 10% surface layer of partially degraded fruit and leaf waste. However, research showed that the solid layer was still attractive to adult SWD. It was found that the waste could be disposed of on field soils, but to avoid further attracting SWD the solid part of the waste needs to be incorporated into the surface of the soil, where it will rapidly degrade. Decisions on where this can be done will vary from farm to farm, but should always be well away from water sources. Growers should check the Environment Agency web pages for more information.

More information can be found in: