Water Primrose in Ponds
Dr. Mario A. Villarino, CEA- Hopkins
Several concerns throughout the last days have caught my attention. The effect of the drought started showing now in trees that are not recovering from the last drought spell. Some damages occurred during the high winds from last week and ponds are getting full again. Some pond are suffering from weed infestations, the one more often asked about is water primrose. Water primrose is a perennial plant that stands erect along the shoreline but also forms long runners (up to 16 feet) that creep across wet soil or float out across the water surface. These runners form roots at their nodes. Leaves range from lance-shaped or willow-like (2 to inches long by 1/2 to 1 inch wide) on the erect stems to round or oval 91 to 2 inches in diameter on the floating stems. Leaves can be green to reddish depending on the species. The single flowers are yellow with 4 or 5 petals depending on the species. Flowers vary in size from 1 inch to 2 inches in diameter. Submerged portions of all aquatic plants provide habitats for many micro and macro invertebrates. These invertebrates in turn are used as food by fish and other wildlife species (e.g. amphibians, reptiles, ducks, etc). After aquatic plants die, their decomposition by bacteria and fungi provides food (called “detritus”) for many aquatic invertebrates. Ducks and other waterfowl will consume the seeds of water primrose. Water primrose can be cut and the roots can be dug up but physical control is difficult because it can reestablish from seeds or remaining roots. There is no known biological control for water primrose, although goats are known to forage on many types of emergent vegetation.
Chemical Control Options
The active ingredients that have been successful in treating water primrose include 2,4-D, diquat, triclopyr, glyphosate, imazamox, and imazapy. Navigate and Weedar 64 are 2,4-D compounds that have been effective on water primrose. 2,4-D compounds are systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides. Reward is a liquid diquat formulation that has been effective on water primrose. It is a contact herbicide. Contact herbicides act quickly and kill all plants cells that they contact. A non-ionic aquatically registered surfactant (see the label) will have to be added to the Reward solution for good results. Renovate is a liquid triclopyr formulation that is effective on water primrose. It is a selective broadleaf, systemic herbicide. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides. An aquatically registered surfactant (see the label) will improve the effectiveness of triclopyr. Rodeo, Aquamaster, Eraser AQ, Touchdown Pro, and AquaNeat are liquid glyphosate formulations and have been effective on water primrose. These are broad spectrum, systemic herbicides. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides. An aquatically registered surfactant (see the label) will have to be added to the glyphosate solution for good results. Clearcast is a liquid imazamox formulation. It is a broad spectrum, systemic herbicide. Systemic herbicides are absorbed and move within the plant to the site of action. Systemic herbicides tend to act more slowly than contact herbicides. An aquatically registered surfactant (see the label) is needed for application. Habitat contains the active ingredient, imazapyr, which inhibits the plant enzyme AHAS (acetohydroxyaced synthase). Habitat is a systemic herbicide that is
effective on post-emergent floating and emergent aquatic vegetation. Imazapyr is effective at low-volume rates and does not contain heavy metals, organochlorides or phosphates, making it safe to humans and livestock. Habitat requires the use of a spray adjuvant when applying on post-emergent vegetation. Clipper is a flumioxazin product and comes in a water dispersible granule which must be mixed in water first and then either sprayed or injected. It is a broad spectrum, contact herbicide. Contact herbicides act quickly. Flumioxazin should be applied to actively growing plants and a surfactant will be needed if the herbicide is applied foliage of floating or emergent plants. Water pH needs to be below 8.5 or flumioxazin will rapidly degrade and lose effectiveness. One danger with any chemical control method is the chance of an oxygen depletion after the treatment caused by the decomposition of the dead plant material. Oxygen depletions can kill fish in the pond. If the pond is heavily infested with weeds it may be possible (depending on the herbicide chosen) to treat the pond in sections and let each section decompose for about two weeks before treating another section. Aeration, particularly at night, for several days after treatment may help control the oxygen depletion. One common problem in using aquatic herbicides is determining area and/or volume of the pond or area to be treated. Many aquatically registered herbicides have water use restrictions Always read and follow all label directions. Check label for specific water use restrictions.Water primrose can be propagated by transplanting whole plants into moist soils during the early spring. However, water primrose can be an aggressive invader of ponds. For more information on pond management or other agricultural topics please call the Hopkins County Extension Office at 903-885-3443.