Fruit fly control by exclusion is an organic pest control method. No poisons are used, merely a covering over the fruit which excludes fruit flies.
The first method of fruit fly control by exclusion could either use mosquito netting, shade cloth or fly screen covering the whole orchard or tree, and supported by a a frame, or a what is known as bagging, a bag covering the individual fruit, or fruit clusters, tied round the stem. The bags can be made of cloth, netting, newspaper or other paper like waxed paper.
The bagging should be done as soon as the flower parts shrivel or drop off, according to experts, because the fruit flowers need to be pollinated before you exclude insects, but in my observation of cucumbers it is too late. The cucumber flowers are open for quite a while and as you can see there is a picture of a cucumber ovary that has been stung while it still has a flower. I tried to get around this problem by hand pollinating the cucumber and bagging it as soon as it first appears on the vine and the flower opens. Tomatoes and capsicum are self pollinating so the fruit stalks can be bagged as soon as possible.
Bagging is labour intensive and requires regular monitoring and bagging through the fruiting season every 14 days, apparently, but I would say this could be too long a period of time. I would monitor daily for fruit that needs bagging. However it is said by multiple sources, to be the most certain method of control and very cost effective in terms of the materials on a small scale, as the cloth bags and waxed paper bags can be reused.
The cucumber out of the bag, healthy with no fruit fly
The cucumber on the kitchen table ready to be made into juicy salad
The small fruit should be thinned to leave space for them to expand to their full size without touching other fruit, and then bagged with a bag large enough to accommodate the fully developed fruit. Shading the fruit does not matter, they fill out due to nutrients coming from the tree sap and photosynthesizing leaves and usually do not need strong sunlight to ripen. In fact when covered they may be larger and sweeter than usual. The bags supply the fruit with protection from other insect pathogens as well as some protection from birds.
Another way of excluding fruit flies is to dust the fruit with a particle film barrier. That is a powder repellent to certain species of female fruit flies, like kaolin, diatomaceous earth or wood ash. This dusting will need to be redone if the plant gets wet where you have dusted, such as after rain or irrigation.
The cheapest and most readily available powder was wood ash,
and I experimented with using it and found it to be only partially successful, and
discouraging oviposition, or ‘stings’. I did not have great enough numbers of
small cucumbers to get a good measure of its success rate. I also wonder
whether wood ash does not burn the plant when it gets wet, after all one makes
lye by mixing water and ash. However the leaves I dusted seemed to take the ash
quite well. Kaolin and diatomaceous earth are available as gardening products
commercially and may be obtained at some nurseries, earth mines or on the
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