Water lilies are a popular choice for water gardens, providing striking color and broad, floating leaves. This aquatic setting attracts a specific set of pests adapted to life on the water’s surface. Identifying the damage these creatures cause is the first step in managing them without compromising the health of the pond. This guide offers appropriate, aquatic-safe solutions.
Identification of Leaf and Flower Pests
Waterlily Aphids (Rhopalosiphum nymphaeae) are common pests that target the above-water parts of the plant, often clustering in dense colonies on new growth and flower buds. These small, sap-sucking insects appear in shades of black, brown, or green and gather on the pads. Their feeding removes plant fluids, leading to the yellowing and curling of leaves, and can destroy developing flower buds if left unchecked.
The Waterlily Leaf Beetle (Galerucella nymphaeae) is a grayish-brown insect about 6–7 mm long, whose larvae are also destructive. Both the adult beetles and their black grubs graze the upper surface of the leaves, creating elongated slots or trenches in the tissue. This grazing causes scarring and ragged edges, and severely affected pads may lose buoyancy and begin to rot.
The Brown China Mark Moth (Elophila nymphaeata) is a frequent problem. Its larvae are nicknamed “sandwich men” for their unique feeding behavior. The caterpillars cut oval or semicircular pieces from the lily pad, folding the tissue to create a protective, portable case. The resulting damage appears as clean, rounded cutouts, and the initial feeding of younger larvae may manifest as tiny holes or skeletonized patches of foliage.
Damage Caused by Snails and Other Aquatic Animals
Damage to waterlilies is caused by various aquatic and terrestrial animals, often leaving behind different patterns of injury. Aquatic snails, such as Ramshorn or Pond Snails, typically consume algae and detritus, but they sometimes graze on lily pads, leaving irregular holes or ragged edges. This damage is generalized and appears less precise than the cutouts left by moth larvae.
Larger aquatic animals frequently target the submerged parts of the plant. Muskrats and beavers, for example, readily consume the starchy rhizomes, which are the main underground storage organs of the waterlily. Damage from these mammals can result in the loss of entire plants rather than just foliage.
Turtles can be problematic, using their sharp beaks to snip pieces from the pads, leaving behind damage that looks as though the leaf was cut with scissors or a knife. Differentiating this clean, linear cut from the ragged grazing of a snail or the distinct, rounded holes of a moth larva helps identify the correct culprit.
Safe and Effective Pest Control Methods
Managing pests in a pond environment requires methods that protect fish and other beneficial aquatic life, prioritizing non-chemical solutions. The simplest approach for aphids is manual removal, using a strong jet of water from a hose to dislodge the clusters and wash them into the pond where fish can consume them. For heavy aphid infestations, submerging the entire plant for up to 48 hours is effective to drown the pests.
For moth and beetle larvae, manual inspection and removal are recommended, involving squishing the insects or removing the affected pads entirely. Introducing natural biological controls, such as the bacterium Bacillus thuringiensis (Bt), is a specific and safe treatment for moth larvae. When sprayed onto the leaves, Bt is ingested by the caterpillars, paralyzing their digestive tract without harming fish, birds, or other pond inhabitants.
The use of chemical pesticides should be avoided unless the product is specifically labeled as safe for aquatic environments, as common garden insecticides are toxic to fish and amphibians. Maintaining a balanced pond ecosystem can provide natural pest control, such as stocking guppies or other small fish that readily eat dislodged aphids and small larvae. For larger pests like muskrats, the long-term solution is to use physical barriers or secure the plant containers to prevent access to the rhizomes.