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June 21, 2010 / Malcolm Dalebö

Black flies running riot!

We are currently besieged by black flies (aphids) on our broad beans. I can’t recall a worse year than this one; they are everywhere on the plants. See how the left stem on the photo is covered totally with black fly, that happened in one day between inspections.
  • Whilst ladybirds will help, sometimes more action is required. Really it is cloud cuckoo land to expect ladybirds to guard a whole crop against black fly, and it is just exaggeration from the organismists to claim that lady birds can control the situation. They can assist with small quantities, but when it gets as bad as we are experiencing it needs something much more!
  • There are a few different colours of aphids and they tend to affect a range of different vegetable crops. 
  • Blackfly or Black Bean Aphid can be particularly devastating to the broad bean plant if not spotted in time.
  • Symptoms: The blackfly can be spotted at the top of the plants as black clusters in the amongst the leaves, under the leaves or flowering buds.
  • If lines of ants can be seen running up and down the plant stem, this is a sign that they are farming the aphids. The ants don’t do any harm to the plant, but the black fly does so remove them as soon as possible.
  • If they have infected the plant, you will see distorted growth on bean pods and withering plant stems with patches of black in the leaf nodes (the part where the leaf joins the stem).
  • Treatment: If the blackfly are in small quantities, squish them between your fingers to remove them from the plant,
  • Washing them off the plants with a hose will temporarily remove them but this will need to be repeated and is not necessarily effective,
  • Washing or spraying the area with mild soap solution may help but will need to be repeated weekly.
  • Best Treatment: When the plant has finished flowering, pinch off the growing tip of leaves at the top of the plant. This is usually where the blackfly congregate in clusters. This does no damage to the plant and removes any further attack to that plant.
  • Prevention: Encourage blackfly natural predators such as Ladybirds, lacewing larvae, hoverfly larvae and parasitic wasps. The encouragement may run to buying a Ladybird Hotel box or similar.
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