Here are the top 5 invasive plants to look out for in your Illinois backyard this spring

Although spring annually brings plentiful blooms to Illinois each year, not all plants are beneficial in your backyard.

Invasive plant species spread quickly across the U.S. and add harmful competition to local ecosystems. Non-native wildlife can disrupt natural processes and become a costly and dangerous nuisance for humans and animals alike.

Here’s what you need to know to recognize invasive species in the Land of Lincoln and remove problematic plants in your neck of the woods.

Why are invasive plants a problem?

Simply put, an invasive species is one that does not naturally belong in an ecosystem. They are often introduced by humans in areas where they are not found historically, according to the University of Illinois Extension, the university’s research-focused outreach program.

Generally, invasive plant species spread quickly, directly contribute to economic or environmental harm and pose a threat to humans in some cases. These species, which can include trees, shrubs, vines, grasses and even flowers, are difficult to extinguish once they establish themselves in an ecosystem.

Invasive species are not to be confused with exotic species, or those that were not present before European settlement centuries ago. Not all exotic species are invasive, but some can be aggressive in new environments due to the lack of natural predators and environmental controls left behind in their homelands.

Invasive plant species spread quickly when limiting factors are not available to slow them down. These types of plants are usually able to grow in many conditions, reproduce rapidly and “green up” in the spring earlier than native plants, giving them a competitive advantage that resembles a head start.

The ecological impacts of invasive plant species are broad. Generally, though, the introduction of non-native plants can change the availability of natural resources, disrupt plant-pollinator relationships, alter the rates of soil erosion and even serve as host reservoirs for plant pathogens. Some species can even harm humans through direct contact.

The Illinois Department of Natural Resources estimates unwanted plants destroy more than 3 million acres of land each year and annually cost more than $35 billion in preventative measures and treatments. Damages, meanwhile, cost approximately $120 billion across the U.S. each year.

“Invasive plants affect all of us as everybody faces increasing costs for food and lumber production while property values and recreational opportunities decline in areas where invasive species have taken hold,” the department says on its website. “The beauty and biological diversity associated with healthy natural areas are being lost as well. Hundreds of invasive species occur in Illinois, and unfortunately, the list grows almost daily.”

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Invasive plants to watch for in Illinois

Though local, state and federal agencies take many steps to combat invasive plants across the country, non-native species remain incredibly common. The University of Illinois Extension, for example, estimates 1 out of every 3 plants in Illinois woodlands, wetlands and grasslands are non-native. Illinois ranks fifth among U.S. states for invasive species introductions, the agency says.

Twenty-six invasive plant species are regulated through the decades-old Illinois Exotic Weed Act. Through regulation, it is illegal for anyone to buy, sell, distribute or plant any parts of the listed species.

Here’s a look at a few of the most common and recognizable invasive plant species found in Illinois.

Amur honeysuckle (Lonicera maackii)

Once considered a beneficial ornamental, this honeysuckle variety is considered one of the most serious forest health challenges in Illinois, writes the Illinois Forestry Association. The species, one of four honeysuckle varieties collectively called bush honeysuckle, is known to impede reforestation and prevent the reestablishment of native plants.

“[Amur honeysuckle] has severely infested our forested natural communities and has displaced native vegetation,” the forestry association wrote in a landowner’s guide to invasive plants. “For this reason, forest management professionals agree that this non-native invader should be managed from Illinois forests.”

To recognize amur honeysuckle, look for an upright, woody shrub that stands between 10 and 15 feet tall with simple, ovate leaves that stretch up to 3 inches and tend to stay green longer than other species in the fall. This species has light-tan bark and yellow or white flowers that bloom in May and June. Red berries arranged in pairs at the base of its leaves are perhaps amur honeysuckle’s most distinct feature.

Pulling these plants by hand can be effective when they are young and the soil is moist enough. Otherwise, amur honeysuckle can be treated through foliar treatments, basal bark treatments or cut stump treatments, the Illinois Forestry Association says.

Giant hogweed (Heracleum mantegazzianum)

Native to southwestern Asia, this invasive plant first appeared in Illinois in 2006. This biennial or short-lived perennial grows between 10 and 15 feet tall and features large, compound leaves that can stretch up to 5 feet wide.

Giant hogweeds are most easily spotted during their flowering stage, which features small white flowers in June or July in flat-topped umbels up to 2.5 feet across. The invasive species belongs in the carrot or parsley family and is often mistaken for poison hemlock, another invasive plant regulated in Illinois.

Notably, giant hogweeds can be harmful to humans. The species’ clear, watery sap can cause photodermatitis, or skin sensitivity to sunlight. The sap can also produce painful blisters or even painless red blotches that can turn purple over time. As such, it’s important to wear gloves when handling this plant and avoid breathing in smoke if this plant is burned nearby, the University of Illinois Extension writes.

Control efforts over the years are believed to have mostly eradicated giant hogweed plants in Illinois, but some may remain. If you suspect you have encountered this species, notify the IDNR or call your local extension office.

Poison hemlock (Conium maculatum)

This biennial weed is just about as dangerous as its name suggests. Poison hemlocks are fatal to humans and animals if ingested.

The plants can stand up to 6 feet tall. They are generally easy to spot thanks to the purple spots that develop on their stems and the white flowers that bloom in the summer when the plants reach their second year.

While all parts of poison hemlocks are toxic, their roots and seeds contain the highest concentration of alkaloids, and the sap produced can irritate your skin.

Complex root systems make it tough to remove poison hemlocks by hand. Mowing or cutting are viable options before plants produce seeds, but avoid burning them, as inhaled smoke can be toxic, the University of Illinois Extension writes.

Autumn olive (Elaeagnus angustifolia)

This invasive plant usually appears as an upright, multi-stemmed shrub standing between 10 and 20 feet tall. You might notice a simple, alternating leaf arrangement with leaves that feature a “glimmering” silver underside — a helpful identification tool.

Autumn olive plants feature a gray, furrowed bark and small, pale-yellow flowers that bloom in April and May. Red drupes with silvery scales function as the species’ primary fruit.

According to the Illinois Forestry Association, autumn olive plants were not always considered the nuisance they are today.

“Autumn olive was once advertised as a beneficial ornamental to provide food and habitat to wildlife,” the association notes. “Unfortunately, today we are dealing with the consequences of introducing this non-native invasive plant to our environment.”

Autumn olive plants can spread rapidly and dominate the understory of Illinois forests, the state’s forestry association writes. The species is particularly known to displace native vegetation and quickly adapt to changing environments, helping it thrive when other plants might not.

Autumn olive roots are very deep and often require heavy machinery to be removed. Follow-up herbicide treatments are a crucial component to control, as the species readily resprouts from its root system if removal efforts are not thorough.

Kudzu (Pueraria montana)

Native to China and Japan, this perennial vine first appeared in the U.S. in the late 1800s. According to the Illinois Forestry Association, kudzu was once promoted for its erosion control properties and was widely planted in the Southeast before its drawbacks were widely studied.

“The vine can completely dominate and smother native forbs, shrubs and trees,” the association wrote. “It is considered one of the more difficult non-native invasives to control.”

Rapid growth is perhaps the most alarming characteristic of this vine. It has been reported to grow as much as 1 foot in length each day and top out at up to 60 feet, the association wrote in a guide. The best growth generally occurs in warmer climates, but this adaptable species can thrive in colder temperatures, too.

Kudzu leaves come in threes and are hairy beneath and on the margins, according to the IDNR. Leaves are broadly ovate and grow between 3 and 6 inches, but they are highly variable. The vines’ flowers, meanwhile, are reddish-purple and produce a distinct grape aroma. Kudzu fruits resemble dark-brown legumes covered with long-spreading hairs.

Controlling kudzu vines requires dedication and persistence. Large, starchy roots make control difficult, but eradication is possible over several years. The Illinois Forestry Association recommends heavy grazing pressure, vine-cutting processes in the summer and even the use of controlled fires to remove old growth and expose new growth.

Combating invasive plants in Illinois

Addressing non-native plants in your neck of the woods is no easy task, but there are steps you can take to make a difference.

The most direct way to help fight invasive plants is by planting native species in your hard. The University of Illinois Extension, for example, offers a handful of native alternatives to invasive plants through an online blog post. You might consider swapping out a pesky buckthorn plant with a highbush blueberry (Vaccinium corymbosum), an acidic soil-preferring variety that produces fruit in the fall.

The IDNR offers plenty of fact sheets and guides covering many topics surrounding invasive plants. Visit dnr.illinois.gov/conservation/invasivespecies/partnershipsandresources.html to find additional information, including brochures for landowners and contact information for environmental organizations in your area.