April O'Neil / news@WHMI.com

Michigan's first detection of invasive hydrilla has triggered an intense response from EGLE and the DNR.

The aquatic plant was found in two West Michigan ponds and is considered one of the world's most invasive aquatic plants.

It was detected for the first time in Michigan, and the Department of Environment, Great Lakes and Energy, or EGLE, confirmed two small populations of the plant in adjacent private ponds on residential properties in Berrien Springs in Southwest Michigan.

The small patches of hydrilla (Hydrilla verticillata) were discovered during routine monitoring following treatment for another invasive plant, parrot feather, which was found in the pond in 2020. Both species are prohibited in Michigan, meaning it is unlawful to sell, possess or import them into the state, and both are on Michigan’s invasive species watch list due to their potential environmental threat.

Hydrilla has several ways of reproducing, allowing it to spread rapidly, outcompete native plants and quickly form dense single-species infestations. Root tubers, turions (buds) and even small plant fragments can develop into new plants, making it very easy for hydrilla to disperse through water or attach to ornamental plants sold for water gardens.

“It’s not clear how either plant made its way to this pond, but seeds or fragments of the invasive plants may have been attached to ornamental plants installed in past years,” said Bill Keiper, EGLE aquatic biologist. “Sediment core samples of the pond and genetic analysis of the plant material are planned to help determine how long the hydrilla has been here and where in the U.S. it might have originated.”

EGLE’s immediate response actions include surveying connected ponds, a receiving stream, and the St. Joseph River to ensure the full hydrilla population extent is known. Herbicide treatments are underway in the infested ponds, targeting hydrilla plants to prevent further tuber production this season. A response plan will focus on preventing the spread of hydrilla beyond its current location, with the long-term goal of eradication.

Hydrilla was introduced into Florida in the 1950s and has spread across the southeast. A separate strain was first detected in Delaware in 1976 and has since made its way through the Atlantic states and several Great Lakes states.

Hydrilla can thrive in both low- and high-quality waters and has been found in lakes, rivers, reservoirs, wetlands, ponds and streams. Plants are generally rooted in sediment in water depths up to 25 feet and remain submerged, with long, leaved stems floating near the surface. Because it outcompetes native plants, it can quickly fill a lake or pond, choking off recreational access.

Though hydrilla can be treated with herbicide, it is difficult to eradicate and can persist in the sediment for years.

More information on identifying and reporting invasive aquatic plants can be found at the provided link.