Invasive species may be characterized as any non-native species that is introduced to a new location, has the ability to spread and causes some kind of harm. Across Illinois and around the globe, invasive species cause significant ecological and economic damage each year.
In the ever-globalizing society we live in, these exotic invaders are a result of either accidental or intentional mixing of biota around the planet. Humans have a long history in this mixing process. As we have become better and better at moving around the planet, the rate of invasive species introductions has paralleled the pace.
Not all non-native species are considered “invasive species.” Tomatoes, peppers and many other vegetable crops we plant in gardens are non-native, however, not at all invasive.
It’s not until a non-native 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 non-natives have some kind of competitive advantage over native species that enables their launch into invasiveness.
Native species have a coevolutionary 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 own 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 bush honeysuckle (Lonicera spp.), or produce prolific quantities of seed, like teasel (Dipsacus spp), non-native species that become invasive have the ability to proliferate in their new homes. Regardless of whether we can identify and notice them or not, invasives, such as the two listed above, are all around and 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 and understanding their impact is identification. Because bush honeysuckle leafs out earlier in spring and holds its leaves later in fall, it is easily differentiated from native species during those times.
Teasel is hard to miss when it starts to flower, being visible along many central Illinois roadways. During this time of high visibility, care must be taken not to further spread seed once it’s viable. Mowing a teasel patch in late summer or early fall can unwittingly spread seed for miles on a windy day. So, along with identification keys, we also need to understand plant life cycles to limit the spread.
One exotic invader is highly visible now across Illinois due to its flower display. Garlic mustard (Alliaria petiolata) is in full bloom in central Illinois making it stick out in woodlands, along fencerows, at the edges of yards or in shade gardens. It proliferates in any area that is semishaded and undisturbed from mowing and other activities.
This exotic, invasive plant was brought to our continent from Europe in the 1800s for its culinary value. Although this plant aggressively invades with prolific seed production – 600 to 7,000 seeds per plant – and allelopathic chemicals it releases into the soil to limit growth of other plants, it is very easily hand pulled. In east-central Illinois, garlic mustard typically flowers around mid-April, with seeds reaching maturity by about mid-May.
Be sure to remove any pulled plants because garlic mustard can still develop viable seeds laying on the ground where it was dropped. Pulled plants should be bagged, removed from the site and burned or otherwise disposed of safely.
Once you learn how to identify garlic mustard, you will start seeing it everywhere. That is also one of its weaknesses, making it readily identifiable to both novice and expert botanists.