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The spring lineup of Iowa’s 10 most invasive threats

Orlan Love, CR Gazette –

Invasive plants and animals, many of them deliberately imported and without natural controls, continue to displace beneficial native species, degrading Iowa’s natural environment. With the early start to spring, many of these species have a leg up this year. So The Gazette asked a panel of experts to help us compile a list of Iowa’s 10 most-troublesome invasive species.

Garlic mustard

Rap sheet: A rapidly spreading plant introduced from Europe in the mid-1800s for medicinal and herbal uses. Its tall, dense stands, first appearing in Iowa about 15 years ago, dominate woodland understories, crowding out wildflowers, ferns and tree seedlings.

Control: It can be controlled through the diligent use of herbicides, hand pulling and prescribed burns.

Asian carp

Rap sheet: The prolific and voracious bighead and silver carp — Asian imports that escaped commercial fish ponds in the South — eat plankton, threatening the food source that sustains most freshwater aquatic life. The silver carp, with its proclivity to leap from the water, also threatens harm to boaters and water skiers. One or the other species has been found in many Iowa rivers and East Okoboji Lake. So far, they have not been found in the Wapsipinicon, Maquoketa, Turkey, Yellow or Upper Iowa rivers.

Control: Only physical barriers, such as dams, can impede their spread, and the effectiveness of dams can be neutralized by floodwaters. Iowa officials are resigned to their gradual dispersal through state waters.

Zebra mussel

Rap sheet: Small Eurasian mollusks inadvertently introduced into American waters via the ballast of oceangoing vessels, zebra mussels were first documented in the Mississippi River in Iowa in 1992. They have since spread to Clear Lake, the former Lake Delhi, the Maquoketa, Shell Rock, Winnebago and West Fork Cedar rivers, as well as Lake Rathbun. The filter feeders directly compete with native species, including mussels and fish fry. They also adhere to hard objects, enabling them to smother native mussels and clog water intake pipes.

Control: Educational programs targeting boaters have been initiated to contain their dispersal.

Emerald ash borer

Rap sheet: This native of eastern Asia, found in far northeast Iowa in 2010, poses a threat to Iowa’s millions of ash trees.

Control: Though the borers cannot be effectively exterminated, the state has implemented a quarantine on wood products in Allamakee County and is conducting extensive monitoring to detect their spread.

Reed canary grass

Rap sheet: This aggressive grass, spread by seeds and rhizomes, displaces native vegetation in low-lying moist areas. It tends to exclude all other vegetation. A European native, it also may have been indigenous to the northwestern United States.

Control: It is extremely difficult to eradicate once established.

Sericea lespedeza

Rap sheet: A warm season, perennial legume native to eastern Asia, first planted in the United States in 1896 for its perceived value for erosion control, livestock forage and wildlife habitat. With a long tap root, thousands of seeds that remain viable for 20 years and its production of a chemical that inhibits growth of other plants, it is well-equipped to outcompete native plants, especially grasses. It has become much more noticeable in Iowa during the past decade and is considered a major problem at the Neal Smith National Wildlife Refuge in Jasper County.

Control: Mowing, burning and herbicides can control its spread.

Leafy spurge

Rap sheet: This major pest of parks and preserves was accidentally introduced from Europe as a seed contaminant. It can completely overtake large areas of land and displace native vegetation.

Control: The release of flea beetles approved for biocontrol has helped reduce population in managed natural areas in the Loess Hills.

Purple loosestrife

Rap sheet: This “pretty” flower, introduced from Europe and Asia in the 1800s for ornamental purposes, invades wetlands, forming dense stands that displace native vegetation. It is found in about half of Iowa’s counties. One plant can produce about 2 million seeds a year.

Control: The release of beetles has reduced population density in some areas but has not been effective in Iowa.

Common buckthorn

Rap sheet: A European native introduced here as an ornamental shrub, buckthorn invades forests, prairies and savannas and can form dense thickets crowding out native shrubs and understory plants.

Control: Once established, it is difficult to remove.

Eurasian watermilfoil

Rap sheet: This submersed aquatic plant forms dense mats in lakes and ponds, inhibiting growth of beneficial aquatic plants, reducing fish habitat and impeding boat traffic. A native of Europe, Asia and northern Africa, it was accidentally introduced into the United States and is now found in about 20 Iowa counties.

Control: It has been effectively controlled with applications of the herbicide fluridone.

Sources: Johnson County Conservation director Harry Graves; Linn County roadside vegetation manager Rob Roman; and Department of Natural Resources biologists: botanist Daryl Howell, zoologist John Pearson, forester Tivon Feeley and aquatic invasive species manager Kim Bogenschutz.

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