The Dirty Seven: Invasive plants threatening Indiana's land, wildlife, and economy

1. Asian Bush Honeysuckle (Lonicera spp.)

Native to Japan, China, Korea, Manchuria, Turkey, and southern Russia, Asian bush honeysuckle was brought to the U.S. as an ornamental plant, valued for its fragrant flowers, wildlife cover, and erosion control properties. Unfortunately, its aggressive nature soon turned it into a widespread invader. Escaping from cultivation, it has now become one of the most common understory invaders in Indiana’s forests.

Asian bush honeysuckles form dense thickets that shade out native plants and prevent forest regeneration. They also increase the risk of nest predation for birds and alter soil chemistry, making it difficult for native species to grow.

Control:

• Hand-pull seedlings before they mature.

• Cut mature shrubs to the ground and immediately treat stumps with a 20-30% glyphosate solution or 8% triclopyr.

Apply foliar sprays in the fall when native plants are dormant.

3. Autumn Olive (Elaeagnus umbellata)

Native to China, Korea, and Japan, autumn olive was introduced to the U.S. in the early 1800s for erosion control, soil improvement, and wildlife habitat. Despite its good intentions, it quickly spread across the landscape.

Autumn olive produces up to 80 pounds of fruit per plant annually, with seeds dispersed widely by birds. Its nitrogen-fixing roots alter soil chemistry, giving it a competitive edge over native plants in prairies, fields, and open woodlands.

Control:

• Hand-pull young plants when soil conditions allow.

• Cut larger plants and treat stumps with a 20% glyphosate or 2% triclopyr solution.

Apply basal bark treatments or foliar sprays and expect to repeat treatments as needed.

5. Callery (Bradford) Pear (Pyrus calleryana)

Native to China and Vietnam, the Callery pear was introduced as a landscape tree prized for its white spring flowers and symmetrical shape. Once a suburban favorite, it has now become a prolific invader.

Spread by birds, Callery pear escapes into natural areas, forming dense stands that crowd out native trees and shrubs. Its weak wood and narrow branch angles also make it prone to storm damage.

Control:

• Girdle or cut mature trees and treat stumps with herbicide.

Remove seedlings before they establish.

7. Crown Vetch (Securigera varia)

Hailing from the Mediterranean region, Crown vetch was introduced in the 1950s for erosion control along roadsides and waterways. Its rapid spread and ability to fix nitrogen made it seem ideal for soil stabilization.

Unfortunately, it aggressively invades prairies and open areas, forming thick mats that smother native vegetation. It also alters fire regimes and nitrogen levels in sensitive ecosystems.

Control:

• Apply triclopyr (2%) or clopyralid (0.25% with surfactant) for best results.

• Use mowing or prescribed burning to weaken infestations.

• Plan for multi-year treatment efforts.