Executive Order 13112 defines an invasive plant as a non-native species “whose introduction does or is likely to cause economic or environmental harm or harm to human health.” State invasive plant lists in the Midwest include all invasive plants which are listed in the federal noxious weed list, as well as plants which are invasive in ecosystems specific to Midwestern ecosystems. While the federal list also includes native plants, the state invasive plant lists concentrate on non-native plants which do not provide a benefit to society which is equal to or greater than any negative impact.
Purple loosestrife
Purple loosestrife (Lythrum salicaria) is near the top of every Midwestern state’s list of invasive plants except Illinois’. It can also be found on the noxious weed lists of the neighboring Canadian provinces of Ontario and Manitoba.
This plant is notorious for crowding out native plants, such as cattails, in the wetlands it prefers.
Once it gets a toehold, purple loosestrife is very difficult to control. Each plant can produce up to 2 million seeds each year. At the same time, its rhizomes, or underground stems, can grow up to a foot each year. Even after the plant is removed, it can regrow from any piece of a rhizome which has been inadvertently left behind.
Even after allowing for its natural rate of propagation, the main problem with controlling purple loosestrife is that it is difficult to see it as a dangerous weed. Because it is a beautiful plant, many people want to plant it in their gardens or let it keep blooming in the wetlands in which it thrives.
Many cultivars have been developed for use in its native Europe, Asia and southeast Australia, but they should not be planted in the Midwestern U.S., or in any part of the U.S., for that matter. In some parts of the Midwest, sterile cultivars of purple loosestrife may be acceptable for container planting.
A good degree of biological control has been achieved through two species of leaf beetles (Galerucella) and three species of weevil (Hylobius transversovittatus, Nanophyes breves, Nanophyes marmoratus). In particular, the leaf beetles are capable of defoliating all of the purple loosestrife plants in an area without harming native plants.
Purple loosestrife can be recognized by its upright purple or pink-purple flowers, which have six petals and 12 stamens. It can be distinguished from similar native species, such as fireweed or spirea, by its angular stalks and paired, unserrated leaves.
Queen Anne’s lace
Queen Anne’s lace (Daucus carota) is listed as a noxious weed or secondary noxious weed in Iowa, Michigan and Ohio. It can also be found in most other parts of the Midwest.
This is another garden cultivar which has found local conditions to its liking. It is still sometimes considered a beneficial weed which can be a useful plant companion to some crops. However, its leaves can cause contact phytophotodermatitis, which is a danger in pastures.
It is related to the domesticated carrot (Daucus carota sativus) and is similarly edible, but only when it is very young. In older plants, the root is too woody to be eaten. This confusion can cause problems in harvesting some root crops.
The lacy flowerheads of Queen Anne’s lace gave rise to its name. Each head is made up of hundreds of individual flowers, which are usually light pink when immature and white when mature. Many flowerheads have a single scarlet flower at the center, which may represent a drop of blood after Queen Anne pricked her finger while tatting lace.
Queen Anne’s lace is very similar visually to poison hemlock, which may be the main reason Queen Anne’s lace is on invasive weed lists. Because of this similarity, Queen Anne’s lace should never be harvested except by an expert.
Poison hemlock
Poison hemlock (Conium maculatum) is listed as a noxious weed in Iowa and Ohio. It can also be found in most other parts of the Midwest.
This plant is much more dangerous than Queen Anne’s lace. This is the same hemlock which was used to kill Socrates after he was condemned. Every part of the plant is poisonous.
Even more dangerous, livestock which have been mildly poisoned by poison hemlock and recovered will return to feed from it again. This makes it an extremely dangerous invasive weed in pastures.
