Ada County Weed Pest and Mosquito Abatement Aquatic Noxious Weeds

Aquatic noxious weed species are found in waterbodies across Ada County. These underwater invaders are mostly new to the area; they were introduced from their native habitats usually as an aquarium plant or ornamental pond plant. Typically these plants reproduce by stem fragmentation. Stems can become detached from the main plant either because of recreation equipment or aquatic life, and the plant pieces take root downstream.

	Brazilian Elodea (Egeria densa) is an aquatic perennial that can reach lengths of up to six feet. Its slender stems form dense stands or subsurface mats that can clog and suffocate local waterways. Its small white flowers grow with three petals and a bright yellow center. The flowers float at the water surface, attached to stems that grow linear to oblong shaped leaves that can reach almost two inches long and 1/4 an inch wide. The leaves grow in a whorled pattern (circular around the stem). The whorls contain four to six leaves that go around the stem. Brazilian elodea reproduces by floating fragments and nodes (found on the stem) which grow into roots. Brazilian elodea is found in shallow, slow-moving waters, lakes and ponds. It was introduced as an aquarium plant and can still be sold as Anacharis and is popular in home aquarium use because of its oxygenation capabilities.
	Eurasian watermilfoil (Myriophyllum spicatum L.) is the first truly aquatic plant listed among Idaho’s noxious weeds list. Eurasian watermilfoil is a perennial weed that forms dense, floating mats that eventually clog the waterways prohibiting native plant growth and inhibiting recreation.  Throughout the summer, the weed’s feathery stems can grow up to 33 feet from the lakebed to the water surface.  In Ada County the plant has been known to stay green throughout the winter, but it typically over-winters as a pale brown plant that lies on the bottom of the waterway.
	Hydrilla (Hydrilla verticillata) is considered to be the most problematic aquatic weed in the United States. A native of Asia, it was first introduced as an aquarium plant that has become versatile in its habitat. Hydrilla can grow in almost any freshwater body including springs, lakes, marshes, ditches, rivers and tidal zones that can range from a few inches to more than 20 feet deep. Remarkably it can grow in areas with as little as 1 percent full sunlight. Because of its tolerance to little or no light, it can begin growing in low-lit areas before other plants can get a chance to start and take hold, thereby outcompeting desirable vegetation at early stages. The plant grows as a submerged aquatic perennial with slender branched setems that can grow up to 25 feet long. It forms dense stands or subsurface mats that suffocate existing aquatic life as it takes over a waterway.
	Parrotfeather milfoil (Myriophyllum aquaticum) - is a submerged perennial weed. It grows up to 15 feet long. It has light gray-green leaves that grow in a featherlike pattern. It has inconspicuous white flowers that grow in the axils between the stem and leaf. It develops in colonies that form large subsurface or surface mats. Parrotfeather milfoil grows best when rooted in shallow water, but can grow in lakes, as well.

 

Because most of these noxious weeds reproduce by stem fragmentation, it’s not recommended to manually control noxious weeds. You can inadvertently let plant parts float downstream, and new infestations can likely grow from those rogue pieces of vegetation. You also need to ensure you remove the entire root system or else the plant will regrow. Below is a list of active ingredients found in herbicides that have proven to be effective against noxious weed infestations. Be aware that some time in early 2010, regulations regarding aquatic herbicide use will change. For more information, call our office at 577-4646. Licensed professional applicators must be consulted before an aquatic herbicide is used.  In all efforts to control aquatic noxious weeds, it is imperative to exactly follow all label instructions, guidelines and restrictions.  While some products use similar active ingredients to terrestrial herbicides, their formulations and instructions for use are different

2, 4-D – Spring to early summer
       Eurasian Watermilfoil
       Parrotfeather Milfoil

Copper – Sunny mornings when water temperature is above 60ºF
       Brazilian Elodea 

Diquat – June through August
       Brazilian Elodea

Endothall Dipotassium Salt – May through August
       Brazilian Elodea
       Eurasian Watermilfoil
       Hydrilla

Fluridone – May through August
       Brazilian Elodea
       Eurasian Watermilfoil
       Hydrilla (Apply in early spring as plants are just starting to grow and oxygen levels in the water are higher)
 
Imazapyr – Apply to actively growing, EMERGED plants
       Parrotfeather milfoil

Triclopyr – Spring to early summer
       Eurasian Watermilfoil

 

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