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Innovations
Using module companion planting of birdsfoot trefoil to control cabbage root fly
Cabbage root fly is a serious pest causing widespread damage in brassica crops. The first generation of flies will emerge from
pupa in April to May and lay eggs at the bottom of the plants. When the maggots hatch, they feed for about three weeks causing
damage to the roots and the stems. It is possible for several generations to occur over the summer.
Roots showing damage by cabbage root fly
Fleece is often used to protect crops against this pest, but laying and maintaining it is time consuming and can make weed
control difficult. Therefore growers would welcome other methods of control. It has been well documented that maintaining a
green under storey reduces the ability of pests to ‘seek out’ the crop, but it is often difficult to achieve this at a level that will reduce
pest infestation without reducing the yield through competition. However, some growers have had found that sowing a single
seed in each brassica module established a population of birdsfoot trefoil that effectively controlled cabbage root fly without
compromising yield.
Brassicas with birdsfoot trefoil sown in the module
A trial at HDRA in 2004, where birdsfoot trefoil was sown in calabrese modules, has shown that companion module sowing
resulted in a small but significant reduction in damage by cabbage root fly, compared to the control plants. Although the effect
was small, it is encouraging that the birdsfoot trefoil still had an effect despite being poorly established at the time that the
calabrese was transplanted. Poor establishment could be attributed to poor seed germination and vigour.
In 2005, three different species of companion plant are being trialled: Birdsfoot trefoil, red clover and yellow trefoil, in order to
ascertain which plants can provide effective control, without reducing yield through competition.
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