Colonies of greenish-brown water lily aphids can form on the upper surfaces of water lily leaves and various pond margin plants.
Control with pesticides is difficult as these cannot be used on plants growing in or adjacent to ponds, meaning prevention is the best cure.
Dead leaves attract aphids,so removing any yellowing or dead leaves from the pond will help keep them away.
Knowing the aphid’s life cycle can be an advantage.
The aphids overwinter as eggs on Prunus species, such as blackthorn, cherries, and plums.
The eggs hatch in spring, and the aphids feed on the new host plants foliage until early summer when winged forms of the aphid develop.
Prudent spraying at this time with a suitable insecticide can help to reduce the numbers transferring to the waterside plants.
Alternatively; gently remove any affected water lilies from the pond or water garden.
Place them in a large bucket, and apply an insecticidal soap or other insecticide to the tub according to the product's instructions.
Leave the lilies in the solution as directed.
Rinse the water lilies in clean water, and place them back in the pond.
For those aphids that survive and migrate to the waterside, control is limited.
In small ponds, aphids can be wiped off the leaves and flower buds.
In larger ponds, directing a strong jet of water at the plants foliage will dislodge many of the aphids and expose them to predation by fish.
In autumn, the winged aphids migrate back to their winter host plants.