Wednesday, December 30, 2009

Is It a Wedding?

Well, they're veiled in white...
And blushing...

Unfortunately, the only romantic thing is that these are my tomatoes, and they're starting to ripen!

Those white 'veils' are fruit-fly exclusion bags. I thought I saw a fruit-fly and acted about a week before Christmas to cover the fruit.

Queensland Fruit Fly is a serious pest for both commercial fruit growers and home gardeners. In Sydney, the fly is active after Christmas -- it likes the warm, humid conditions. It lays its eggs in a whole range of garden fruits, but particularly likes stone fruit, and tomatoes and capsicums. QFF doesn't attack cucurbits, but a bad infestation will see them in almost everything else. Home gardeners normally see them in tomatoes, though cherry tomatoes are rarely affected.

I should mention that the tiny flies commonly seen hovering over those grapes you forgot to eat, or in the less reputable fruit shops, are vinegar flies (Drosophila), not Queensland Fruit Fly.

The fly usually lays its eggs near the calyx, making the 'sting mark' less obvious (though in a bad infestation you will see sting marks everywhere!). Its maggots then eat the fruit from the inside. When they're ready to pupate, they will have eaten enough of the fruit's insides for it to fall to the ground. The maggots burrow into the soil to pupate before hatching out as adult flies (a bit smaller than a house-fly). In ideal conditions it takes about a month for a fly to go from egg to sexual maturity, and they lay eggs for weeks afterwards...

Thus everyone who has grown up with home-grown tomatoes here has also grown up with the sight and stench of rotting tomatoes, and the sound of cranky gardeners calling down curses upon Bactrocera tryoni.

How do we control it? Well, the most important thing is to practice good hygiene. Firstly, fruit trees should be looked after so they do not shelter fruit flies (there is a legal requirement that I strip my quince tree of fruit at the end of April to prevent fruit fly over-wintering in them). Make sure the tree is not too tall to check the fruit. Fallen or infected fruit should be either solarised or frozen. My Dad's preferred method was to add the fruit to his 44-gallon drum of compost tea!

To be truthful, the best control of fruit fly is through regular spraying of systemic insecticide. I'm a busy person with children, and I like the other minibeasts in my garden, so there are a host of reasons I don't want to spray. My contacts with other gardeners have led me to believe that baits and lures are not terribly effective, so I am going with barriers instead.

We have had dry summers for the last few years, which have reduced the numbers of QFF in Sydney. I am concerned that this year, as vegetable gardening has been booming in popularity, and there are many novice tomato growers around, we will see QFF in plague proportions.

Your Department of Agriculture or Primary Industries will have a fact sheet about Queensland Fruit Fly for your area. Please read it and follow its directions. Be especially careful to follow the local regulations if you are travelling into a fruit fly exclusion zone this summer.


Jamie said...

Here's wishing you a happy new year, Chookie, and tomato gluts aplenty!

Rock rose said...

Hoe interesting to read about that rotten old fruit fly. I hope you are successful in keeping them at bay. They are so tiny that the regular netting wouldn't keep them out. None of those here, but we do have the leaf footed bugs and harlequin bugs. Such fancy names for wretched marauders. Not to mention the raccoons and possums. it is such fun trying to get a good harvest!
happy New gardening Year

Kelley @ magnetoboldtoo said...

I remember as a kid travelling to Port Macquarie and having to dump our fruit at the border.

Happy New Year babe!