Lily pads, a generic name for water lilies (Nymphaea spp.) float on the surface of a pond, producing attractive flowers throughout the growing season. Despite their beauty, lily pads reproduce through rhizomes in the pond bed and can take over the pond if not contained in underwater pots. Fragrant water lily (Nymphaea odorata) is a particularly troublesome lily pad species with the ability for a single rhizome to form a 15-foot circle in just five years. Eradication typically requires using several control methods, with the number of methods depending on how bad the problem is.
Grasp the lily pad stems as far below water as possible and pull the plants out of the ground, pulling up as much of the rhizomes as possible. In a large backyard pond, wear hip waders and perform this task from inside the pond.
Drag a bow rake across the bottom of the pond to dislodge and pull up remaining rhizomes. Dig the rake tines into the soil at the bottom as much as possible so you are not simply scratching the surface.
Step on and turn a twisting weed popper tool in the soil in the bottom of the pond. This specialized tool features claws arranged in a circle that loosen the rhizomes as you twist and pull them up as you lift it out of the soil. This option might only be necessary if the lily pads return aggressively.
Gather any lily parts from the top of the pond, using your hands if you are inside the pond, or by dragging the surface with a broom rake or net. The rhizomes should float to the pond surface, but it doesn't hurt to rake the soil at the bottom of the pond to gather all the rhizomes. Discard the plant parts in a green materials waste bin or in your compost pile.
Cut through the stems below the water to separate the lily pad from the rest of the plant. You can reach across or wade in most ponds.
Remove all the cut lily pads with a bow rake and dispose of them in your compost or green waste bin.
Clip off any new lily pads as soon as they develop on the water's surface. This could take persistent clipping for up to three years to completely kill the lily pad rhizomes. Removing the pads prevents the plants from photosynthesizing and making food, causing the the lily pad rhizomes to eventually die.
Cover the soil in the bottom of the pond with a benthic barrier fabric, a type of weed barrier that blocks sunlight and prevents rhizome sprouts from growing. This type of barrier only works after you've successfully removed the lily pad vegetation after killing the plants. Apply the barrier immediately after removing the vegetation or in early spring before any remaining dormant rhizomes awaken and produce new lily shoots.
Mix a glyphosate herbicide product labeled for aquatic use with a non-ionic surfactant and water in a garden sprayer or spray bottle, achieving a final dilution of 2 to 3 percent glyphosate. Exact mixing instructions vary with different products, depending on the percentage of glyphosate in a concentrated product. Aquatic glyphosate herbicide concentrated at 54 percent, for example, should be mixed at a rate of approximately 2 2/3 ounces per 1 gallon of water. Another 2 to 3 ounces of non-ionic surfactant helps the herbicide to coat the lily pads instead of rinsing away in the water. If you wish, add 1 ounce of spray marking dye so you can keep track of which lily pads you have sprayed.
Spray the top of each lily pad with the glyphosate herbicide solution until thoroughly coated, but avoid applying so much it drips into the water. Wear protective goggles, long sleeves and long pants when applying the herbicide and keep children and pets out of the area while you're working with the weedkiller. Allow approximately 10 days for the herbicide to transpire through the leaves and down to the rhizomes, killing the lily pads. The lily pads will first turn light green, then yellow and brown as they die.
Drag the dead lily plants out of the pond with a bow rake or garden rake. Discard the plants in a compost pile or green materials waste bin.
Spray a second round of the glyphosate solution to treat any remaining lily pads or any new plants that sprouted after the first application. Wait another 10 days or until the plants die, then remove the dead water lilies.