Management key to fruit fly numbers

With controversial decisions around the use of pesticides, as well as fears surrounding loss of production, a new approach to managing Mediterranean fruit fly has come to the fore. It relies on teamwork, according to Perth Natural Resource Management regional landcare facilitator Shayanna Crouch.

Ms Crouch said combating Medfly in WA relied on commercial growers and home gardeners working together. “As Medfly is hosted by so many plants, it needs to be managed on a wide scale. This includes commercial growers and backyard growers,” she said. “We believe the issue with Medfly is with its management, and prevention is a key priority for Perth NRM.”

Medfly is reported to infest more than 200 types of fruit and vegetable species worldwide. It is mandatory to control the declared pest in several local government areas of WA, including Kalamunda, Mundaring, Serpentine-Jarrahdale and Swan.

With summer approaching, Ms Crouch said Medfly activity depended on warmer temperatures.

“The warmer weather encourages the proliferation of insect species including Medfly, as they use the increased food supply in the spring and summer months to enhance their populations in this ideal climate,” she said.

“The life cycle of the Medfly is centred around the female Medfly laying eggs in thin-skinned fruit as it starts to mature.

“The larvae'''''' develop in the fruit, making it inedible, and then jump out of the fruit while it’s still on the tree or when it’s on the ground. The larvae then dives into the soil where they pupate to become adult flies.

“The pupa emerges from the soil some time later as an adult fruit fly to begin the cycle over.”

Ms Crouch said the management of the pest needed to break this cycle to be able to have a greater proportion of edible fruit.

“Management needs to be continual. Having a management plan can help to ensure growers are doing all that they can to prevent the spread of Medfly,” she said.

Management plans for commercial and home growers are slightly different. “Management of fruit fly starts by determining its presence in the garden or orchard, which can be a lot more difficult in metropolitan areas where the fly moves easily between properties that are in close proximity,” Ms Crouch said.

“Keeping a watchful eye all year is necessary and the use of traps is a simple way to achieve this.”

Ms Crouch said the best way to control the pest was by baiting fruit trees with a protein bait and an approved insecticide diluted with water, and either spot bait or band bait on the trees leaves at waist to chest height.

Female flies are attracted to the protein, which they need to produce eggs, and then the insecticide kills them before they are able to lay eggs in the fruit.

Insecticides that are registered for domestic use in controlling Medfly include Malathion or similar.

“Details on registered use of a chemical are found on the chemical container’s label. Users are advised to always check labels for the registered use and application rate before use,” Ms Crouch said.

Baiting should be conducted weekly as a minimum and continued for at least two weeks post-harvest. Rain events of more than 5mm will render the insecticide ineffective.

Ms Crouch said trapping was also effective. “CeraTraps and homemade traps have a protein attractant and a pesticide to kill the trapped flies,” she said. “They need refreshing weekly but in conjunction with baiting should significantly reduce the presence of Medfly.

“Netting and bagging of trees and fruit also helps to prevent Medfly gaining access to the fruit. This can be timely and very effective, although somewhat costly.”

Orchard hygiene is at the heart of every management plan and includes the destruction of any fallen or unwanted fruit.

Ms Crouch said growers should seal any unwanted fruit in a black plastic bag and leave the bag to “cook” in the sun. This fruit can then be disposed of as waste or buried at least 1m below the surface of the ground.

This will break the life cycle of the fly and hamper its ability to breed.

“Combining all of these practices can significantly reduce the presence of Medfly within a garden or orchard,” Ms Crouch said.

Research into Medfly management and prevention practices is also on the radar of the Department of Agriculture of Food. One pilot the department is championing in Carnarvon aims to control the pest based on a sterile insect technique.

The pilot involves using an improved strain of male-only Medfly sterilised by x-ray in DAFWA’s South Perth rearing facility. It was designed to take place in conjunction with management techniques such as good orchard hygiene, baiting and traps.

The large-scale release of the sterile fruit flies into plantations around Carnarvon aims to overwhelm the wild male population and outcompete to mate with wild females, which will produce infertile eggs. Their release will take place later this year.

For Perth Hills growers, adopting management techniques has resulted in Medfly numbers remaining low. The success of backyard growers in this fight will depend on their proximity to other unmanaged fruit tree sites.

Ms Crouch said information on managing the pest would be one initiative presented in the Perth NRM marquee at this year’s Karragullen Expo on October 8.

“We will be showcasing some of the work we have accomplished over the past 12 months, including our Healthy Soils Healthy Rivers program and the collection of chill data from orchards in the Perth Hills,” she said. “We are analysing chill data to increase our understanding of how climate change is affecting fruit production.”

Ms Crouch said another project run in conjunction with the Hills Orchard Improvement Group aimed to investigate, better understand and manage ground water resources to adapt to the State’s drying climate.

“Perth NRM will also be hosting an array of groups in our marquee again this year, including DAFWA and the MyPestApp, the WA Horse Council and the Nursery and Gardens Institute of Australia,” she said.

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