THE ISSUE:  Hydrilla 

Hydrilla (Hydrilla verticillata), a submerged, aquatic perennial weed native to Asia. It was introduced to the U.S. for use in aquariums. It invades rivers, streams, lakes, ponds, marshes, canals, ditches, and reservoirs. This plant is extremely aggressive allowing it to completely overtake bodies of water. 

Hydrilla has small bright green leaves that are pointed, serrated and have at least one sharp tooth under the middle of the leaf. Leaves are arranged in whorls, generally there are 5 leaves in a whorl, but there can be 3-8. Stems are branched, slender and can grow up to 25 feet in length. This plant is generally rooted but can also survive as a free-floating plant. It can reproduce from fragments, potato like tubers, buds, and seeds. Its ability to reproduce from fragments and tubers makes it extremely difficult
to control. 

Look-a-likes: American Water Weed (Elodea Canadensis) and Brazilian elodea (Egeria densa)

Integrated Pest Management (IPM) Options: 

Prevention— Never dispose of aquarium contents in water ways. Always wash and clean recreational equipment before transporting. 

Mechanical— Hydrilla plant material can be removed from bodies of water, but it can reproduce through fragments, tubers, and seed. So, this is not always an effective control option. 

Cultural— small populations may be controlled by covering them with an opaque fabric that blocks sunlight. Reducing the water level so that the soil can dry out might also be an option. 

Biological—Triploid grass carp have been used to consume hydrilla, this species of fish is exotic and thus its introduction is highly regulated.  

Chemical—Contact local authorities about using Herbicides to control hydrilla in water ways. Always read and follow herbicide label directions.

Justin Hatch, University of Idaho Extension Agriculture Educator in Caribou and Bear Lake Counties. 208-547-3205 [email protected]