THE ISSUE:  Feathered mosquito fern 

Feathered mosquito fern (Azolla pinnata) is a small free-floating aquatic annual that is native to Africa and Asia. It invades stagnate areas in ponds, ditches, and rivers. As feathered mosquito fern reproduces it forms large dense mats that float on the water surface negatively impacting recreation and irrigation. 

Fine hairs that cover leaves enable this plant to float on the water surface. Leaves are very small (0.04 – 0.08 inches long), rounded and occur in overlapping pairs. When the plant is young it is bright green or grey green and as it matures it takes on a reddish hue especially at the base of the plant. It reproduces from spores and plant fragments. Up to 64 spores can be produced on the underside of fruiting structures. Spores and plant fragments can be transported by currents, wildlife, and recreational equipment. Under favorable conditions this plant can double in size in 3 days. 

Integrated Pest Management (IPM) Options: 

Prevention— Learn how to identify this plant and report sightings. Never dispose of aquarium contents in surface waters. Always clean recreational equipment before transporting. 

Mechanical— Water surface can be raked to remove plant material. Be sure to compost plant material far enough away from the body of water that plants/plant parts cannot be washed back into the water. 

Chemical—Oxygen depletion is a concern whenever using a chemical to control weeds in a body of water. Always read and follow herbicide label directions.

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