Davey Tree Flipbooks

38 POISON HEMLOCK (Conium maculatum) PLANT DESCRIPTION Poison hemlock is a biennial weed that can be seen from early spring to midsummer as a 3–8 foot tall, upright, single stemmed, branching plant with showy white flower heads. Poison hemlock can also be found in spring or fall as a low-growing seedling or rosette. Colonies are easily spotted in late spring to early summer with showy white flower heads. LEAF: Leaves are dark green, glossy, and deeply divided with pointed lobes similar to a fern leaf. STEM: Stems are slightly zigzag, hollow, smooth, and hairless with purple spots. FLOWER: Upward pointing white flowers emerge in early summer in a loose umbrella formation of several clusters. SEED: Seeds are yellowish green, small, and round with vertical ridges. The seeds fall near the parent plant in the fall. REPRODUCTION: The seeds function as the primary means of reproduction germinating in both fall and spring. Most seeds are dropped around the parent plant and can also be spread by animals, birds, or by water. WHY IT IS NOXIOUS: Use caution when in contact with this plant. Poison hemlock is highly toxic to humans if ingested. If sap contacts the skin, severe blistering can occur, especially when combined with sun exposure. SEASONAL IDENTIFICATION WHEN TO FIND: Late spring to midsummer is the easiest time of year to identify and locate poison hemlock in flower. In late summer, look for large colonies in flower or in seed production. Poison hemlock also persists into winter. SPRING IDENTIFICATION = MODERATE Seedlings and rosettes can be found covering the ground, often in colonies growing under dead mature plants. The fern-like leaves are large, broad, dark green, and glossy. SUMMER IDENTIFICATION = EASY Mature poison hemlock features include zigzag, and smooth hollow stems with purple blotches and white umbrella-shaped flower clusters at the ends of branches. FALL IDENTIFICATION = EASY TO MODERATE Mature poison hemlock plants have died off by this time leaving plant skeletons standing. Seedlings and rosettes can usually be found under dead mature plants by late fall. Seedlings and rosette patches are usually darker green than most other vegetation at this time. WINTER IDENTIFICATION = MODERATE Dead mature plants can persist into winter and can be identified by zigzag and hollow stems. Seedlings and rosettes stay green over winter but are dormant. SIMILAR-LOOKING SPECIES WILD CARROT (Daucus carota) young plants look most similar, but leaves are more deeply lobed and are not glossy. Hairy, solid stems are the main difference. Flower heads are white and flat topped. GIANT HOGWEED (Hercaleum mantegazzianum) has similar umbrella-like flower heads, but they are flat topped. The size of giant hogweed, especially the leaves, differentiate this plant from poison hemlock. Stems are hollow with purple splotches but are covered in hairs. All features of giant hogweed are generally much larger than those of poison hemlock. LOW HIGH ohio distribution roadside distribution growth seeds ability to dominate difficulty of control WHERE TO FIND: Poison hemlock is quite common in Ohio, usually found in large patches or colonies in unmowed areas along Ohio roadways. Look behind guardrails and on slopes along the road. Poison hemlock grows best on well-drained slopes with full sun, but can also tolerate wet soil and shaded areas along the edge of wooded environments. CONTROL METHODS: MECHANICAL: Mow or cut only from spring to early summer to maintain visibility or to reduce seed production. Hand pull with gloves. Use caution! Avoid sap contact as it can cause severe rashes. CHEMICAL: Make directed applications from spring to early summer with selective herbicide. Make applications before flowers bloom. Fall applications to young plants can also provide control. CULTURAL: Plant tall fescue in early fall. RECOMMENDATION SUMMARY: Poison hemlock is toxic, germinates in spring, lives for one full season, and overwinters as a rosette. In the second spring the stems bolt and produce flowers and seeds before dying. Accomplishing control should not be difficult with many opportunities to prevent seed production. For best control results make herbicide applications in spring to early summer. Fall applications to rosettes and seedlings can also be effective. Use directed applications because poison hemlock is usually found in dense patches. If it is sporadic in large areas, use broadcast applications with selective herbicide. Mow at flower emergence to reduce seed production. Plant sap is toxic! Use caution when hand pulling to control or cutting to reduce seed or plant height. Plant tall fescue in early fall and allow to grow tall in spring to compete for space and to shade out seedlings. Failure to control poison hemlock will allow this highly toxic, tall growing, and competitive weed to form dense patches, thereby crowding out more manageable vegetation. biennial x 2 RIVM LEVEL OF CONCERN

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