Hi Kimby, when you say in the growbags I take it you mean on the compost? Aphid blackfly live underneath the leaves of plants sucking the life out of them and these need squashing between thumb and finger. Sciarid blackfly or fungus gnats live on the compost where they lay their eggs. The larvae then feed on the plants roots. Yellow sticky papers hung up catch the sciarid flies. Which type of blackfly have you got?
|