The issue: Curlyleaf pondweed

Not all weeds are above ground. Curlyleaf pondweed (Potamogeton crispus) is a freshwater, aquatic, perennial weed from Eurasia that spends its entire life underwater, except for the small flowers. The plant tops die off in the summer. The decomposition results in low-oxygen conditions that stress fish populations. The unique life cycle and aggressive reproduction reduces ecological diversity.

Curlyleaf pondweed sprouts in September and October; does most of its growth in the spring; then dies back in the warmer, summer waters. The most distinguishing characteristic is the long (up to 3 inches), narrow (up to half-inch) leaves, which have a very wavy margin with fine teeth.

Curlyleaf pondweed spreads predominantly by a vegetative structure called a turion that are produced on the root system, but also through rhizomes in the river and lake sediment. Because the turions form and separate from the parent plant during the summer months, the best time for control activities is in early to mid-spring, when plants are young.

Integrated pest management options:

· Prevention: Always be on the lookout for new weed infestations; inspect and clean boats, trailers, and other watercraft.

· Mechanical: Hand pull in early spring before native plants begin to sprout.

· Cultural: Winter drawdown of ponds, canals and ditches

· Biological: Grass carp have moderate preference for curlyleaf pondweed, but typically prefer native species.

· Chemical: Early spring application usually avoids issues with later-sprouting native aquatic plants; aquatic herbicide formulations of diquat, endothall, and fluridone; use with extreme caution as drift may affect downstream plants. Be sure the weed and landscape or crop situation are listed on the label. Always read and follow herbicide label directions.

Combine them:

Combine different IPM options over a period of years to help improve the effectiveness of your efforts.

For more information, contact Ron Patterson, University of Idaho Extension horticulture/agriculture educator in Bonneville County, at 208-529-1390 or