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How to: Fruit fly control

Fruit fly is an insect pest that has devastating effects on fruit trees and fruiting crops. Once a male and female fruit fly mate, the impregnated female lays her eggs in the ripening fruit, where maggots hatch and feed, spoiling the fruit and causing it to rot. While there are many fruit flies, the two that you need to look out for are the Queensland fruit fly (Bactrocera tryoni) and Mediterranean fruit fly (Ceratitis capitata). Fortunately, there are ways you can control these pests, without resorting to out-dated, harmful chemicals. Read on to find out more about how to protect your garden.

Background
The Queensland fruit fly (Q-fly) is native to the tropical and subtropical rainforests of Queensland northern New South Wales. The NSW Central Coast was thought to be the southernmost outpost for decades, but since the Millennium Drought (2001-2009), I’ve received questions on my radio program from Victorian gardeners concerned about the pest. Research now confirms Q-fly has spread down the entire east coast of Australia.

In addition, the vast tropical fruit production across the Top End’s Ord River Scheme, and extensive network of vegetable farms, vineyards and home gardens further south have encouraged its spread. Both Q-fly and Mediterranean Fruit Fly (M-fly) have invaded the entire west coast down to Perth, creating a $300 million nightmare across Australia.
It’s clear that Q-fly is highly adaptive. Acclimatising to warm and cool climates has resulted to the insects’ territorial expansion to virtually all Australian home gardens. Instead of mating, Q-fly now infest existing autumn fruit like loquats and persimmons, and even protein-rich compost heaps to over-winter. This combination allows their numbers to increase dramatically in summer and autumn to wreak greater havoc in spring. While cold conditions will kill eggs, larvae and pupae, mature adults will survive winter.

Chemical controls
In the last decade, the Australian Pesticides and Veterinary Medicines Authority (APVMA), banned the use of the common Q-fly cover spray insecticides – dimethoate (Rogor and Sabateur) and fenthion (Lebaycid) – due to potential human health risks.
This led to an increase in research and development for safer sprays and lures. Previously, fruit fly baits included arsenate of lead, DDT, nicotine sulphate, and tartar emetic. Today Malathion (or Maldison) are used in many pre-mixed fruit fly traps, like OCP’s eco-lure. Unfortunately, this is not effective against M-fly.
There has also been research into male-specific lures using naturally occurring or synthetic pheromones. They’re often better at monitoring the arrival of fruit flies, than controlling them, but are an important part of a holistic approach to controlling fruit fly. These include Cuelure and methyl eugenol, which are the standard Q-fly controls worldwide.
Food-based baits containing Spinosad, like Yates Success Ultra and OCP’s eco-naturalure, attract and kill both female and male Q-fly and M-fly. Apply to the foliage, not the fruit as incorrect applications can cause problematic results. A natural garlic and pyrethrum-based product, Richgro Naturally Based Fruit Fly Concentrate, may be useful as a fruit fly repellent.

Best practice
Controlling Q-fly is a year-round activity. Install permanent traps around the garden to help indicate the presence and build-up of Q-fly numbers. Regularly replace lures (in the traps) as per the label instructions to ensure effectiveness. As soon as fruit fly presence is confirmed, baiting should commence alongside netting.
Multiple forms of netting are available, from exclusion bags for covering individual and fruit clusters to branch and whole tree covers. The mesh size must be small enough to exclude the flies and must not touch fruit and be applied after flower pollination.
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Practicing good garden hygiene is also essential. Remove any infected fruit and any unwanted fruit fly host plants. Cover exposed compost heaps, and ensure your neighbours are doing the same to help control and prevent fruit fly. Otherwise, all efforts may be fru­­itless.

Graham thanks Andrew Jessup for his assistance with the latest information for this article. Andrew Jessup, Horticultural Market Access Entomology, Janren Consulting.

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Author: Words: Graham Ross (Images: Shutterstock)