Cabbage rootfly in compost

Question ...

I have just harvested a cabbage, which I grew in a large pot. When I took it out of the soil, I noticed that there were cabbage rootfly maggots. Should I throw the potting compost away, or can I use it again?

Answer ...

The cabbage rootfly has white legless larvae, up to 8mm long and will only attack the roots of plants of the cabbage family, so you can use the potting compost again for plants of other species.

The adults of this flying insect lay eggs in soil near, or occasionally on, host plants. Pupae overwinter in the soil. Damage is usually worse in late spring and early summer, but a second and even third generation may continue to damage plants into autumn. Cover brassicas (wallflowers and stocks also) with non-woven fleece or fine mesh immediately after sowing or planting. Or, protect individual plants with a cabbage root fly mat. Plant into a slight hollow; in the event of an attack, earth up to encourage new root growth. Intercrop with French or dwarf broad beans.

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