Horned Pondweed (Zannichellia palustris) is a submersed aquatic weed found in every state in the continental United States. It can be found in shallow freshwater lakes and ponds.
Horned Pondweed is a delicate, underwater perennial with branched slender stems that sprout from creeping rhizomes. Long thread-like leaves are smooth edged without teeth. They grow from ½ to 3 inches long and are oppositely arranged or whorled on the stem. Leaves gradually taper to a point at the tip. Tiny banana shaped, slightly curved seeds are flattish in shape and serrated on one side. They attach to the stem at the leaf base in clusters of 2 to 4. Seeds are produced in early spring and are released into the water in June. Weeds die back in the early Summer when water warms and seeds are released. This cycle repeats in the fall when water temperatures begin to cool. Weeds reproduce from both seeds and rhizomes.
The entire weed and its fruit is eaten by wildlife and is also a fantastic food producer for trout. The weed foliage also provides good habitat for aquatic animals.
Horned Pondweed grows aggressively. This aggressive growth will form dense mats that interfere with fishing, boating and swimming. The water temperature and oxygen levels will also be reduced when these aquatic weed mats begin to die in late Summer.
Control methods:
1) Physical removal using both Weed Raker and Weed Razer is an option for seed and root reduction. Seeds viability is low but will vary from year to year. Physical removal by weed raking or weed cutting can be difficult, because new weeds can sprout from seeds and rhizome fragments left behind. Repeated mowing may also produce short term results.
2) Fluridone Liquid and Sonar Granular are both fluridone based aquatic herbicides. They are best applied early season, prior to seed, when new weeds begin to sprout. Both pond weed killers must be applied to an entire pond or a minimum of 5 acres, and cannot be used for spot treatment.
3) Aquathol Super K Granular and Hydrothol Granular are both endothall based, fast-acting contact options. They are best applied prior to seed, when new growth is 12-14” tall and water temperature is 65°F or warmer. Repeat treatment may be needed to contact all the foliage.
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