Aquatic plant problems FAQs

My water lilies have become infested with greenfly. However, there are goldfish in the pool, so I dare not use an insecticide. What can I do to control these pests?

Water-lily aphids (Rhopalosiphum nymphaeae) attack not only water lilies but also a wide range of other aquatic plants. Since you cannot use insecticides I suggest you weigh down the foliage of the lilies and other plants and keep them submerged for a few days, to allow the fish to feed on the aphids. As this aphid species overwinters as eggs on various species of Prunus (peach, plum, cherry, almond, etc.) you can reduce the risk of infestation next year by applying a tar-oil winter-wash to these trees, if you have any, in mid-winter.

Irregular holes have appeared in some of my water-lily leaves and a few of the leaves have become ragged and rotten. What caused this damage?

If you examine the undersides of the holed leaves you will almost certainly find oval-shaped ‘cases’ made of pieces of leaf. These cases are made by the caterpillars of the brown china moth (Nymphula nymphaeata) which are eating your water lily leaves. The best method of control is to pick off these cases by hand.

Narrow linear holes have appeared in some of the leaves of my water lilies. Could these be caused by the small dark-brown beetles which are present on the leaves?

These water-lily beetles (Galerucella nymphaeae) are indeed the culprits: both the adults and the dark-coloured, soft-bodied larvae feed on water-lily leaves. One method of control is to hose the leaves to wash the beetles into the water, where the fish can feed on them. Alternatively, keep the infested leaves submerged for a few days.

Sorry, comments are closed for this post.