Utah's exotic plants are non-natives introduced into the state from elsewhere, usually by humans who saw some value in planting them. Many of them, however, have become invasive because none of their natural enemies live in Utah. They steal soil nutrients form Utah's native plants and food and habitat from birds and wildlife. They threaten agricultural crops, forests and fisheries, says Defenders of Wildlife. The National Park Service has proposed treating several of Utah's exotic plant species.
The National Park Service has proposed diffuse knapweed (Centaurea diffusa) for treatment in Canyonlands National Park. Native to Eurasia, 1- to 2-foot diffuse knapweed produces chemicals that make the soil inhospitable for other plants. With a deep taproot that makes it difficult to eradicate, it has spreading branches rising from a rosette of basal leaves. It produces lobed green foliage and spiny, greenish yellow bracts with white or purple flowers. The wind carries the plumed brown seeds, allowing the plants to spread. Spraying with herbicide from the time its rosettes appear until it's ready to bud is the most effective form of control.
Field bindweed (Convolvulus arvensis), says the Utah-Idaho Cooperative Weed Management Area (UICWMA), is a European native plant with seeds that can survive up to 50 years. Field bindweed is common along Utah's roadsides and in pastures and fields.This is an exotic proposed for treatment in Arches and Canyonlands National Parks, and at Hovenweep and Natural Bridges National Monuments. A usually prostrate, green-leaved vine, it grows to 6 feet and occasionally climbs over other plants. It can root up to 10 feet deep. Between June and September, this perennial has morning glory-like pink or white blooms. It spreads by roots as well as seeds. Control it with regular herbicide applications from spring to frost.
Saltcedar (Tamarix chinensis), an exotic perennial shrub or tree from Eurasia, is proposed for treatment in Canyonlands and Arches National Parks and Hovenweep and Natural Bridges National Monuments. Growing from 5 to 25 feet high, it takes over lakeshores, stream banks, pastures and rangelands. Large individuals of this exceptionally thirsty species, says the UICWMA, can soak up as much as 200 gallons of water per day. Saltcedar has long, thin branches with small green leaves on reddish stems. From early spring until late autumn, it bears heavy clusters of white or pink flowers. One tree can disperse as many as 600,000 airborne seeds each year. Saltcedar also spreads by its roots. Spraying plants with herbicide from early summer to late fall is the recommended control.