Mature poison hemlock in a crop field. Photo by James Wolff
Many people are noticing plants growing along roads, across pastures, and in ditches. They resemble wild carrot (Queen Anne's lace) except they are two or three times the size. The assumption is these weeds are actually the giant hogweed identified in Northern Indiana several years ago.
This is not the case. In reality, most of these plants are poison hemlock with some elderberry plants. Poison hemlock resembles its relatives the wild carrot and giant hogweed.
While appearing similar, poison hemlock differs from wild carrot by noticeable purple blotches along the smooth stem. Wild carrot stems are small, green and hairy. Additionally, poison hemlock has doubly-compound leaves and grows to twice the height of wild carrot.
Poison hemlock appears tall but giant hogweed lives up to its name by reaching heights over 8 feet. Both stems exhibit purple coloring but it is more pronounced on the hairy stem of the giant hogweed. Leaves of giant hogweed are also larger, reaching several feet in length/width, and lack the lacy appearance of poison hemlock's smaller, finely-lobed leaves.
The Maine Department of Agriculture, Conservation and Forestry has a useful chart showing other look-a-likes and their differences. The Michigan Department of Agriculture and Rural Development also describes giant hogweed and explains only 2 percent of samples submitted to a lab are confirmed as giant hogweed.
While poison hemlock does not cause the severe skin irritation of its relative, it is still toxic when ingested and care should be taken when handling the plant. Your fears of a giant hogweed invasion can rest at east. However, I still caution you to take care in identifying weeds and wear the proper protection when handling them.
Please review the additional resources listed below and contact your local Purdue Extension educator for any questions you may have about weed identification, dangers, or controls.