Leading berry company Driscoll’s is carrying out research in Spain to find the most effective methods of controlling the invasive vinegar fly Drosophila Suzukii that can wreak havoc on crops. 

The pest is a serious threat to soft summer fruits, and was first identified in Europe in the fields of southern Spain in October 2012.

It thrives in mild weather and humid conditions, which make it particularly prevalent in many areas of Spain and Europe where polytunnels are commonly used to grow crops.

Driscoll's agronomy manager in Spain, José Manuel Aguilar, is closely involved in the research of controlling the vinegar fly in test locations within the country.

He told www.freshfruitportal.com it was important to keep humidity levels in the tunnels to a minimum by taking measures like cutting back plants to reduce their density.

"If you control the density of the crop you're going to improve ventilation and remove humidity from inside the canopy," Aguilar said.

"Normally we remove the lower leaves of the plants to increase ventilation in the lower part of the of the canopy. We use irrigation pipes in the soil bed and so normally the humidity is concentrated in the lower part."

Aguilar also explained that the common practice of discarding overripe fruit on the soil surrounding the crop often led to sharp increases in nearby Drosophila Suzukii populations, and so it was important to remove fruit from the fields.

The use of traps is another method that has proved successful, whereby 100 of them are used per hectare.

The Driscoll's researchers are also going to start collaborating with a university in Spain to control the pest with the use of an entomopathogenic fungus.

Aguilar went on to emphasize that the best solution to the problem would be a carefully balanced combination of several measures, which would need to be adjusted to suit each individual farm.

When asked whether a possible strategy could be to catch male vinegar flies, sterilize them and then release them, Aguilar said it hadn't been tried yet but was definitely a possibility.

"We are learning a lot, so we can't discard any strategy to control the pest. We are doing trials with traps, and this year was really successful - we discovered that the use of pesticides alone is not effective," he said.

"You need to combine different strategies - ventilation, agrochemicals, trapping, cleaning. A lot of things need to be mixed to find the best solution.

"We also learned that every farm is different. In soils that have more clay, for example, there is increased water retention which means more humidity and more flies. In sandy soils it's the opposite."

Driscoll's has been working alongside the local government in southern Spain to share data and come up with the most effective strategies.

"The relationship is really close. I would say that our main relationship is information sharing. The government had their own monitoring system, but when we showed them our one they preferred it and decided to adopt it," Aguilar said.

"We compare the data and come up with a strategy."

As Driscoll's operates in many regions of the world, it is able to compile all its information and share it with the rest of the industry.

In Europe, the vinegar fly has been detected in Portugal, Spain, the U.K, France and Belgium and is also found in the northern areas of Morocco.

Because of the berry industry's globalization, the fly has potential to spread as fruit is sold from one country to another if adequate controls are not in place.

"If you have weather conditions that are favorable for the development of the fly, normally you are going to have the pest because it's really explosive. We worked out this fly could travel 2km [1.2 miles] per day, which is a lot," Aguilar said.

Aguilar added he believed it would be extremely difficult to completely eliminate the fly since it could survive by laying eggs in a wide range of crops, but by working together the industry could prevent Drosophila Suzukii from spreading and reduce the negative effects experienced by growers throughout the world.

Photo: Martin Hauser, via Wikimedia Creative Commons

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