how to control cabbage root fly

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How to control cabbage root fly


wilted plant due to cabbage fly larvae in how to control cabbage root fly
wilted plant










Yesterday, when I was pulling some weeds between my turnips and my cauliflower, I saw some limp cauliflower plants. Fortunately, I only found two plants that were in a bad condition. 

I pulled out the wilting plants and on both plants I found maggots. This was the job of the cabbage fly larva. This means I had to be concerned about my other brassica plants too. So I had to know how to control cabbage root fly.

The cabbage fly

cabbage in a row in how to control cabbage root flyThe cabbage fly larva feeds on the roots of brassica plants like cauliflower, cabbage, Brussels sprouts…
The fly itself doesn’t do any damage but the female lays her eggs near the stem of Brassica plants. When those eggs hatch, the problem is getting out of hand.
The maggots eat the smaller roots first – at this stage the plants can still be saved – and then start feeding of the main root, weakening the plant at first and killing it in the end.

How to get rid of the cabbage root fly?

So, how to get rid of the cabbage root fly and her larva’s.
Well, there are some ways to combat the cabbage fly larva. The different possibilities have to do with the size of the field and the danger of the products or materials.

The least dangerous option:

In garden centers or on the internet, you can find different products that can help you prevent the attack of the larva by taking away the opportunity for the fly to lay eggs near the plant.
The first one that comes to my mind, is the cabbage collar, this is a circular sheet of some kind of carpet. Or you can find biodegradable collars.
In the middle of the sheet is a hole which is cut through on one side right to the outside of the circle. This way the collar can be fitted around the stem of the plant. The sheets have a diameter of about 8 centimeters or 3,15 inches. This size is big enough to stop the cabbage fly larva of getting to the stem and roots of the plant.
The fly always tries to lay the eggs as close as possible to the stem. She’ll even climb down the hole made by the stem swaying in the wind. With the collar in place, the fly can’t lay eggs near the stem so if she lays eggs at the edge of the sheet, the larva will die before they reach the stem.

Insect mesh grow tunnels

A second way to fight the fly is the use of growth tunnels with insect mesh. I’ll buy some as soon as possible so I don’t have to use insecticides.
These tunnels are about 45 centimeters or 17,72 inches wide, 45 centimeters or 17,72 inches high and 3 meters or 9,84 feet long. The use of these tunnels is highly recommended if you like to garden ecologically, so without the use of pesticides. The tunnels can also be used for different kinds of plants ( for instance, carrot fields)

Insect mesh fence

A third system is being used on a professional basis but may also be suited to use in a private garden.
Due to the fact that cabbage flies fly on a very low level, there is the possibility to surround the brassica field with fences of insect mesh of about 1,8 meters or 5,91 feet high.
The top of the cage can be open but the fences have an outward flap in a hook of 45° which works as an eel pod, keeping the flies underneath the flap and with no way to reach the brassica field. Currently, this system is being tested in Belgium but the first success came from Canada. This system can be used for fields up to 2 hectares or 4,94 acres.

moderately dangerous option:

root damaged by cabbage fly larvae in how to control cabbage root fly
root damaged by the larva

I look at this suggestion as fairly dangerous because there is no immediate threat to humans and mammals but this product is highly toxic to insects and marine life. I’m talking about the product called “Conserve” containing the biological insecticide spinosad.

Spinosad is an insecticide which is composed of a mixture of chemical substances. These substances are the product of a fermentation process of the soil bacterium Saccharopolyspora Spinoza.
You can use the product diluted on the leaves or in the ground. When it’s used to attack insects above ground it has to be sprayed on the leaves. This can be detrimental to many good bugs in the garden (for instance the honeybees, bumblebees, parasitic wasps…)
For use against the cabbage root fly, the product has to be diluted with water (There is an explanation on the box on how to do this) The mixture has to be poured on the ground around the stem of the plant ( 100 ml per plant). The product seeps into the ground, killing the maggots.
Using the product the above way is not dangerous for the ‘good bugs’ which are flying around but it does kill a lot of creatures living in the soil. It’s not harmful to worms if used as explained on the box. But too much spinosad in the ground will kill the worms. This can not be said for the other insects and invertebrates living in the soil. These critters (for instance the springtails) will die in no time.

Really dangerous option:

This option concerns the use of chemical pesticides. Personally, I have no experience with chemical fertilizers nor do I have experience with chemical insecticides, so I will not be expanding on this option any further. I just want to you to keep in mind that chemical pesticides can also be harmful to humans and mammals.


So now we have some options and we know how to control cabbage root fly. The mechanical way of working (the tunnel or the fences) might be labor-intensive but I do think it’s a good way to avoid trouble while still cooperating with nature.
So this is it for this article on how to control cabbage root fly, I hope you’ve found it interesting. If so, please share with friends and other gardeners.

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