For a Queensland fruit fly free spring – act now!
Robin Gale-Baker, from Sustainable Macleod, discusses Queensland fruit fly. This is one of a series of articles she has written about growing techniques (see right hand sidebar). She has also written a number of articles about growing various vegetables, herbs and fruit trees.
I’ve heard a number of people refer to April as the end of the Queensland fruit fly (QFF) season, presumably because their summer veggies and summer fruit have now been harvested. However this is a misunderstanding. The QFF season never ends because the QFF life cycle is a 12 month cycle. Now (April) is the time to do everything in your power to make sure that the larvae do not enter the soil and pupate ready to hatch in the spring.
The first jobs are:
- Remove all fallen fruit from the ground.
- Remove any fruit left on trees that cropped in summer.
- Remove any veggies such as tomatoes or peppers or chillis still on the bushes.
- Dispose of any of the above by cooking (baking, boiling) or microwaving, or solarising for 7 days in double black plastic bags, and then wrap anything not in plastic bags in newspaper and place all in the waste bin.
- Do not put any infested fruit, even treated fruit, in the compost as this is an ideal breeding ground.
Now turn your attention to autumn fruit. Autumnal fruits such as feijoas, guavas, and autumn raspberries are heavily infested with QFF in many gardens right now. Feijoas and guavas fall readily to the ground especially when infested. On the tree, infected guavas will look like droopy sacks and feijoas will have dark, soft patches and obvious holes. Rake out any fruit under the tree and strip any fruit that appears to have QFF and dispose of as above. With raspberries, you will need to break them open and check whether there are larvae. These will be creamy coloured and evident from their wriggling. Note that white spots inside the raspberry are not QFF but rather part of the seed. Feijoas and full size guavas are climacteric fruits, meaning they will ripen off the tree, so pick them early and ripen them indoors.
Then if you have chooks, let them loose under your fruit trees and they will scratch out any pupae and clean up larvae on the surface. Borrowing a few chooks for a day or two may even be an option!
Winter fruit such as persimmon and tamarillo need to be picked as soon as they start to colour and then ripened indoors. Citrus cannot be harvested until it is ripe as it does not ripen after picking so spray with kaolin clay (sometimes called/branded as ‘overhaul’).
Quite soon the female QFF will die, leaving the males to overwinter in warm places in your garden. These males will then mate with the females that hatch from pupae in the spring, and produce the first flush of QFF infestation around September (the second flush will be from December onwards). QFF males assemble in leks – groups of about 10 – and live through the winter in either the canopy of trees (such as lemon trees) or in trees adjacent to warm spots (such as compost heaps or chook pens). It is therefore a good idea to put Wild May traps which attract males in the canopy of trees in these areas to reduce their number. Do this from May onwards. Place them 1.2-2 metres high on the east side of the tree where it will get the weak morning sun (placing them in hot sun evaporates the liquid quickly and denatures it).
Now is the time to prepare a plan for the spring. There’s a lot of evidence from local growers about what works. Taking the following measures can result in your fruit and vegetables being completely free of QFF next season. It’s all about taking early action!
- Net all vegetables that are subject to QFF infestation at the time of planting, making sure the net is secured to the earth in some way – wood, earth, pegs etc. (Many nurseries sell wide net off the roll, which is both less expensive and better than the narrow net in packages. You can buy exactly the amount you need. 2x2mm or 1x3mm exclusion netting is suitable.)
- Net all fruit trees and tie the net to the trunk or weight it down or use net sleeves over branches of fruit or spray all fruit with kaolin clay so that they look ‘snowy’. This will have to be done 3 or 4 times throughout the season, and trees checked after heavy rain. Spray the fruit on all sides.
- Prune your fruit trees so that you can easily reach all fruit and easily net or spray.
- Net all berries as it is too difficult to remove kaolin clay from them (kaolin washes off easily from larger fruit).
- Net any indigenous edible fruit bushes.
- Put out protein baits which attract both males and females but don’t rely on these to do the job or to tell you if there is QFF about – take action earlier (as above) so that when they do arrive, it won’t matter. Put these out in August. I recommend Cera-traps which last a whole season. Making your own protein baits is a possibility but as they need to be changed every 5 -7 days, and most people don’t do this, I think the cost of Cera-traps is worth it.
- Be wary of relying on online advice from well meaning people about when QFF is about in your area. There are many reasons that QFF may be in one person’s garden but not another’s. Much better to take action before there is any possibility of QFF being around.
- Clean up all fruit now (April).
- Put out Wild May in May and continue through the year.
- Put out protein baits in August and continue through the year.
- Net all seedlings at time of planting, especially summer seedlings.
- Net fruit trees or use net sleeves to cover fruiting branches or spray with kaolin clay.
Thanks for all the guidance. Some additional experiences below which you might care to comment on. The QFF maggots ‘trojan-horsed’ into our garage in the picked quinces. All quinces looked good when picked, but 100% of them were infested. I had used a good quality insect net for exclusion, however the tree had grown and I made the mistake of leaving gaps in the net below the tree.
While cutting up the quinces to treat them, many pupating globules (look like 5mm long eggs) fell out into the boxes. Thinking I had cleaned all boxes, I returned them empty to the house loft, only to find hatched Queensland fruit flies about the loft windows maybe a fortnight later. So beware what fruit you carry into the house for storage, even the garage. QFF seems to have the ability to leave a 5-10mm thick ‘husk’ of unspoiled fruit so the fruit looks good outside, but is fully infested inside.
After treating the cut quinces with boiling water then standing overnight to cool, I dug the quince pieces well into a veggie bed as for green manuring. I presume this puts the fruit out of reach of the QFF for further egg-laying to continue the cycle.