Invasive species can be characterized as any nonnative species that is introduced to a new location, has the ability to spread and causes harm. Across Illinois and around the globe, invasive species cause significant ecological and economic damage.
In the ever-globalizing society we live in, these exotic invaders are a result of either accidental or intentional mixing of biota. Humans have a long history in this process, and as we have become better at moving around, the rate of invasive-species introductions has paralleled that pace.
Not all nonnative species are considered invasive. All the tomatoes, peppers and other vegetable crops we are planting in our gardens right now are nonnative, but not at all invasive. In fact, many of us can attest to the difficulties of keeping them happy and healthy in our vegetable gardens.
It’s not until a nonnative plant begins to damage natural ecosystems, typically by altering habitat or simply outcompeting native species for resources, that it is considered invasive. Only a select few nonnatives have some kind of competitive advantage over native species that enables their launch into invasiveness.
Native species have a co-evolutionary history that has carefully sorted out competition over time and established the functioning relationships among species that creates their native ecosystem. An invasive species is able to cheat this well-established order by inserting abilities to compete that were gained in its native ecosystem but are a distinct advantage in their new home.
Whether it’s the ability to leaf out earlier than native species, such as with bush honeysuckle (Lonicera spp.), or produce prolific quantities of seed, like teasel (Dipsacus spp), nonnative species that become invasive have the ability to proliferate in their new homes. Invasives inhabit a wide range of locations on the landscape from pristine woodlands to the mowed ditches along our interstates.
The first step in controlling these species is identifying them. Since bush honeysuckle leafs out earlier in spring and holds its leaves later in fall, it is easily differentiated from native species during these times. Teasel is hard to miss when it starts to flower, being visible along many roadways. However, mowing a patch in late summer or early fall can unwittingly spread seed for miles on a windy day.
Right now, one exotic invader is highly visible due to its flower display. Garlic mustard (Alliaria petiolata) is in full bloom in central Illinois, making it stick out like a sore thumb in woodlands, along fence rows, at the edges of yards or in shade gardens. It proliferates in any area that is semi-shaded and undisturbed from mowing and other activities.
This invasive plant was brought here from Europe in the 1800s for its culinary value. As its name implies, this biennial herbaceous plant is edible, adding a strong garlic flavor to food.
Although this plant aggressively invades with prolific seed production (600-7,000 seeds per plant) and allelopathic chemicals it releases into the soil to limit growth of other plants, it is very easily pulled out by hand. With its greater visibility during flowering, right now is a key time to control it. In our area, garlic mustard typically flowers around mid-April, with seeds reaching maturity by about mid-May.
However, be sure to remove any plants that are pulled, as garlic mustard can still develop viable seeds laying on the ground next to where it was dropped. Pulled plants should be bagged, removed and disposed of safely.
Once you learn to identify garlic mustard, you will see it everywhere, which can be depressing. However, that is also one of its weaknesses, making it readily identifiable to novice or expert botanist. In fact, I have found that my kids love to pull this plant. Its stalk is easy to reach and the plant comes out of the ground with little effort, especially after soil is loosened from spring rains.
Take some time this spring to learn how to spot this plant, and the next time you hike a favorite trial, bring a plastic bag to haul out some garlic mustard. The native plant species will thank you by filling in the ecosystem they were intended to inhabit.