Saturday, October 3, 2015

Fruit fly control

We had about 500 people visit us for Sustainable House Day and about 200 asked me about fruit fly control (mostly due to this article in the local paper).

Fruit fly are a huge problem in West Australia and many other parts of the world and people struggle to control them. These days few people want to use nasty chemicals which many commercial growers still use. People are also busy so they don't want time consuming methods. So, here's my solution: a chemical free, set and forget method I call 'Net and Forget'.

We have two types of fruit fly here, the Queensland and Mediterranean types. Here's an example of public enemy number one.

First things first. This method works best for stone fruit and apples, for citrus see lower down. The first thing you need to do is prune your tree to a maximum height of 2-2.5 metres. This makes everything you do on the tree easier: pruning, harvesting, pest and disease control, netting, etc. Fruit above 2.5m will rarely be harvested anyway and will fall to the ground and spoil. Using ladders is dangerous and not even I want to risk a fall for a few fruits. Fruit trees are very hardy so don't worry about hurting the tree when you prune. The best time of year is after fruiting in autumn.

So, now you've got your compact tree you can start on infrastructure.

You'll need the following:

Four 2m lengths of re-bar (steel reinforcing bar), 12mm gauge. Sold at your hardware store (cost $28).

Poly ethylene 25mm pipe, approximately 8-10m per tree. This is high density poly pipe which is strong and flexible. Sold as Vinidex PE pipe here in WA at hardware stores in the plumbing section (not retic). Costs $2/m in 25m rolls =$20/tree.

One nut and bolt larger than 50mm. Cost $2.

Fruit fly netting with 2mm mesh. These come in a variety of sizes and you'll need to measure your tree to find out the size you need. The best I've seen are from Green Harvest online, the 2.5 x 2.5m ones are great (cost $80). They're also sold locally at Dawson's and Bunnings.

Place the rebar half a metre into the ground so you have 1.5m protruding. These need to be placed around the tree in a square approximately 2m apart.

Then slot the PE pipe over one length of rebar and over to the other corner diagonally. Do this again with the other corners and you have a dome a bit like a tent.

Drill holes in the centre of the pipes to attach the pipes to each other with the nut and bolt.

This is your frame finished and you can leave it up all year if you want.

Then you throw the exclusion net over the frame and weigh it down at the bottom with some stones or branches. Now your tree is fully protected from fruit fly! You should put the netting on when all pollination has finished of course and do it soon since fruit fly can lay eggs when fruit is as small as a pea. When you've finished harvesting you should remove the net and store it ready for next year. Below is our apricot tree in the front garden.

If you think you may have fruit fly larvae in the soil under your tree place a trap inside the net for the first year, after that you should be OK. You can also do this for a week or so if you've trapped any flies inside your net. My favourite traps are Cera Traps and you can buy them locally at Dawson's or Bunnings or online at Green Harvest.

The cost of this system is hefty: up to $130 per tree. But the frame will last forever and the netting should last 5 years if you take care of it. So, over 20 years that's less than $20 a year. Think about the money you'll save on buying fruit too, how much do fresh organic apricots cost these days? Probably $20 a kilo, so if you get a kilo of apricots then you've made your money back.

One note: double grafted trees are not great for netting. One half often flowers at a different time to the other and it's very hard to net half a tree! For this reason I do not recommend buying multi graft stone fruits or apples.

A quick and easy method is to just buy the net and throw it over the tree canopy. Then tie it to the trunk and you're done. Any fruit which falls is caught by the net too. You will find that branches and leaves grow into the net and get distorted using this method.

What about citrus I hear you ask. Well, citrus are tricky because often you'll have flowers at the same time as mature fruit due to the slow ripening of citrus. This means you can't net them because pollinators need access to the flowers so you'll need to go for trapping. Again, I recommend Cera Trap, an organic and very effective type. Place a few of these around your garden for maximum effect. You can make your own traps with old plastic bottles with holes drilled into them and there are plenty of homemade trap recipes on the web.

Now, sit back and relax while your fruit ripen!

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