How to Control Water Garden Pests
WATER LILY APHID
I have had some luck spraying infested plants with a hose to knock the aphids into the water where hungry fish will eat them. I have also left the plant completely submerged for the day. The aphid lets go of the plant and gets eaten atop the water.
WATER LILY BEETLE
This is an extremely destructive pest, it is a very specific little pest, and only attacking water lilies, and it becomes a major problem. The small, dark brown beetles and shiny black larvae are found on the water lily pads, where they strip away the epidermal layer of tissue, leaving the slimy tattered remains to decay. This leaves squiggly line like holes in the pads.
Adult beetles hibernate in pond side vegetation during the winter, emerging in late spring and early summer when the lily pads reach the surface of the water. They deposit clusters of eggs on the leaf surfaces. In one week black larvae with distinctive yellow bellies emerge and feed on the foliage until pupation takes place. There can be four broods in a season. Once again you can hose off the plant and hope the fish eat them. You may have to pick them off by hand.
FALSE LEAF MINING MIDGE
A most irritating pest that can be seen in many garden pools, the false leaf-mining midge seems to be particularly troublesome with small water lilies cultivated in tubs and containers. The minute larvae of this pest eat narrow tracery of lines over the surface of floating foliage. This eventually turns brown and rots. There is no control, except regularly spraying affected plants with clear water to dislodge the pests. However, in severe cases, it is a good idea to remove all the floating foliage, together with the pests, to give the replacement growth a fresh start.
While the ram shorn and Japanese black trapdoor snail are valuable consumers of algae, which rarely if ever devour desirable garden plants, this is not true of many other snails. Species like the greater pond snail or freshwater whelk, and the fountain bladder snail can be extremely destructive. Aquatics with floating foliage are particularly vulnerable. One way of ridding the pond of these pests is to float fresh lettuce leaves on the surface of the water over night by morning remove lettuce with snails on it from the pond.