MSU Extension Bulletin E-2935 June 2012 Giant Hogweed Please destroy previous editions

An attractive but dangerous federal noxious weed. Have you seen this plant in Michigan?

Hogweed is hazardous Wash immediately with soap and water if skin exposure occurs. If pos- Giant hogweed is a majestic plant sible, keep the contacted area cov- that can grow over 15 feet. Although ered with clothing for several days to attractive, giant hogweed is a public reduce light exposure. Giant hogweed health hazard because it can cause se- (Heracleum mantegazzianum) is a vere skin irritation in susceptible people. federal noxious weed, so it is unlaw- The plant exudes a clear, watery sap that ful to propagate, sell or transport this causes photodermatitis, a severe skin plant in the United States. The U.S. reaction. Skin contact followed by ex- Department of Agriculture (USDA) posure to sunlight may result in painful, has been surveying for this weed since burning blisters and red blotches that 1998 and several infestations have later develop into purplish or blackened been identified in Michigan. For more

USDA APHIS PPQ Archive, USDA APHIS PPQ, Bugwood.org Archive, USDA APHIS PPQ USDA scars. The reaction can happen within information about giant hogweed, visit It’s a tall majestic plant, 24 to 48 hours after contact with sap, the Michigan Department of Agricul- and scars may persist for several years. ture and Rural Development at www. but DON’T TOUCH IT! Contact with the eyes can lead to tempo- michigan.gov/exoticpests. rary or permanent blindness.

Use common sense around giant hogweed Don’t touch or handle plants using Don’t transplant or give away your bare hands. giant hogweed plants or seeds. These

USDA APHIS PPQ, Bugwood.org USDA Don’t allow children to play in actions are illegal. giant hogweed. They may sometimes Do wash immediately with soap Arm burn from giant hogweed. use the long, hollow stems for tele- and water if giant hogweed sap gets on scopes or peashooters. your skin.

How to recognize giant hogweed Giant hogweed is a biennial or base. Coarse, white hairs are espe- perennial herb capable of reaching 6 to cially prominent circling the stem 12 feet in height in Michigan. The best at the bases of the petioles. time to identify giant hogweed is dur- ing flowering. Plants sprout in early spring from seed or tuberous root- stocks. Plants can quickly form a solid canopy and displace native vegetation. • Stems are 2 to 4 inches in diam- eter, hollow, stout and ridged with purple blotches and coarse, white hairs. Stems may approach 12 feet in height in Michigan. • Leaf petioles (leaf stems) are hol- low, purple-blotched and some- Wearing gloves, a technician holds a

Terry English, USDA APHIS PPQ, Bugwood.org English, USDA Terry times nearly solid purple near the giant hogweed stem. (1) • Leaves are very large on the underside are — up to 5 feet across. stiff, stubby and approxi- Lower leaves are com- mately 0.25 mm long, pound with three large, and they may not be deeply cut leaflets. Each visible to the naked eye. leaflet has deep, irregular The leaf underside looks lobes and coarse, sharp smooth and scaly. teeth on the margins. • Flowers are white, This giant hogweed leaf is 3 feet long. At right, a flower. APHIS PPQ, Bugwood.org English, USDA Terry Upper leaves are similar clustered into a large, in shape, smaller, often compound umbel with be 2.5 feet wide. The not divided but simply a flat bottom and gently plant flowers from June deeply three-lobed. Hairs rounded top. Umbels can to August in Michigan.

Growth stages 1) Dead stems. After 2) Fruit. Mature fruit 3) Seedlings. Seeds 4) Rosette of leaves. producing seeds in late sum- consist of two sections. germinate from early spring Leaf clusters sprout from mer, the plants die and leave Each section is oval in throughout the growing overwintering roots each stems standing into winter. outline, 7 to 13 mm long, season. Seedlings form a year for two to five years At this point seeds have 6 to 10 mm wide, flattened vegetative rosette pattern of until the plant flowers. been dispersed to germinate and tan-colored with usually growth the first season. the following spring or in four prominent dark lines future years. (oil tubes).

5) Flowering stems (see picture at top right of page). Plants bolt and flower in midsummer after rosette plants accu- mulate enough energy reserves. This may take from two to five years.

Look-a-likes: Similar plants commonly mistaken for giant hogweed Cow Parsnip often hairy throughout and circle the stem at the node. but these are flat-topped and [Heracleum maximum (aka no greater than 2 inches Although present on both smaller at 6 to 10 inches H. lanatum)] is a native in diameter. Hairs on cow leaf surfaces, the soft hairs across. Cow parsnip gen- plant very similar to giant parsnip are fine – soft and are primarily confined to erally flowers from early hogweed. Cow parsnip is fuzzy – rather than coarse as the lower leaf surface and June through early July in smaller, reaching a maxi- on giant hogweed. Leaves have a velvety appearance. Michigan, typically several mum height of 6 to 8 feet are compound, up to 2.5 feet These lower leaf hairs are weeks before giant hog- in Michigan. Unlike giant across, and contain three about 1 mm long and are weed. Mature fruits have hogweed, the stem may large, broad leaflets. Leaf- often the best distinguish- two eggshaped sections. be entirely green or have lets are deeply lobed with ing characteristic from giant Each section is 7 to14 mm only a slight purplish cast. coarsely toothed margins. hogweed. Cow parsnip has long and tan to pale tawny Stems are deeply ridged, Stem leaves are smaller white flower clusters similar in color with four vertical often hairy below the nodes, and their leaf stalks almost to those of giant hogweed, purple lines (oil tubes).

(2) Angelica (Angelica atropurpurea) can be easily distinguished from giant hogweed by several features. Stems are uniformly waxy green to purple, smooth, hollow and up to 2 inches in diameter. Mature leaves are feet in width. The globular, Angelica seldom reaches gan. Mature fruit have two double or triple compound softball-sized clusters of 8 feet in height and typi- oblong-oval sections that with numerous leaflets and greenish white flowers are cally flowers from mid-May are ribbed, 4 to 6.5 mm long are capable of reaching 2 up to 12 inches in diameter. through mid-June in Michi- and usually flattened.

Poison hemlock (Conium maculatum) is a multibranched, non-native biennial plant ranging from 4 to 9 feet tall. The waxy stem has purple blotches and the entire plant is Eric Coombs, OR Dpt Ag, Bugwood.org Eric Coombs, OR Dpt smooth. The fernlike leaves are bright green and may Leaves and flowers resem- ingested. It generally flow- side, and yellowish to gray- appear glossy. Small, white ble those of wild carrot. Poi- ers in late May through late brown. Each fruit section is flowers are arranged in son hemlock has a disagree- June in Michigan. Mature 2 to 3.5 mm in length with numerous, small, flat-topped able “mousy” odor, and the fruit have two sections that prominent, wavy, somewhat clusters on all the branches. entire plant is poisonous if are oval, flattened on one knotty lengthwise ribs.

Wild carrot (Daucus carota), also known as Queen Anne’s lace, is a common biennial weed in Michigan that forms a basal rosette of leaves the first year followed by an erect, 3- to 4-foot flowering stalk the following year. Stems identical to those of culti- cluster, often with a single, shaped sections. Each sec- are erect, branched, hollow, vated carrot. Lower leaves purple flower in the cluster tion is flattened on one side, rather thin and covered with are considerably larger center. Wild carrot flowers yellowish to grayish brown, short, coarse hairs. Leaves than the upper stem leaves. from July to September. 2 to 4 mm in length and are very finely dissected, White to sometimes pinkish Mature fruits have two egg- ridged with barbed spines. lacy to fernlike and virtually flowers form a flat-topped

Wild parsnip (Pasti- naca sativa) is a non-native species easily distinguished from the above species by its yellow flowers. Wild parsnip may cause photo- dermatitis similar to that caused by giant hogweed. (3) Identify Report it! Accurate identification is the first step toward eradicating this invasive, hazardous weed. Review the “Look-a-likes” section of this bulletin, and if you If you receive confirmation believe you have a giant hogweed plant, e-mail photographs of the plant, leaves, from MSU Diagnostic Services that flower head and stem where the leaf joins the stem, to Michigan State University your plant is giant hogweed, you Diagnostic Services at [email protected] for confirmation. You will receive a can report the plant’s location to the response letting you know whether the plant is giant hogweed. Midwest Invasive Species Infor- mation Network (MISIN) at: www.misin.msu.edu. Control The MISIN web site lets you mark on a map the location of an If you want to remove giant hogweed, be sure to take appropriate precau- invasive species such as giant hog- tions to prevent exposure to giant hogweed’s sap by wearing protective cover- weed so that collectively, commu- alls, rubber gloves, eye protection and sturdy shoes. Place plant parts in heavy nities can identify and address these duty garbage bags. Do not mow, cut or weed-whack to try to control the plant concerns. mechanically. Its large perennial root system will soon send up new growth. Also, these tactics are risky because they increase the opportunities for you to come in contact with the plant’s sap. Small seedlings can be controlled with a labeled herbicide containing www.msue.msu.edu glyphosate, but most references state that a mature giant hogweed plant will not succumb to a single application. Controlling with a herbicide will require close attention, reapplication to basal sprouts and a keen eye for germinating seedlings, which can germinate for several seasons. Anyone using a herbicide to control giant hogweed must do so according to pesticide label directions.

Prevent www.michigan.gov/mdard Giant hogweed is spread naturally by seeds, which can be wind-blown MSU Integrated Pest Management and scattered several feet from the parental plant or may be carried by water to Program. www.ipm.msu.edu invade new areas. People are usually responsible for spreading giant hogweed This bulletin is based on a 2005 version by over long distances. Seeds or young plants from a friend’s garden, planted in Steven A. Gower and Robert J. Richardson. new locations, help spread this weed quickly over distances much greater than the plant would spread naturally. The dried fruit clusters are sometimes used in This material is based upon works supported by the Cooperative State Research, Education and decorative arrangements and, when discarded outdoors, can start a new infesta- Extension Service, U.S. Department of Agricul- tion. ture, under agreement number 2001-41530- 01102. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the authors and do not necessarily About giant hogweed – Where did it come from? reflect the view of the U.S. Department of Agri- culture. This information is for educational pur- Giant hogweed, native to the Caucasus region of Eurasia, is a member of the poses only. Reference to commercial products carrot or parsley family (Apiaceae) that was introduced into Europe and North or trade names does not imply endorsement or bias against those not mentioned. Reprinting America in the early 1900s. Its massive, majestic size and imposing appearance cannot be used to endorse or advertise a com- made it desirable for arboretums and gardens. Because of its persistent and in- mercial product or company. vasive habit, giant hogweed soon escaped cultivation and became established in MSU is an affirmative-action, equal-opportunity rich, moist soils along roadside ditches and stream banks, and in waste ground, employer. MSU Extension programs and ma- tree lines and open wooded areas. The plant’s name, Heracleum mantegazzia- terials are open to all without regard to race, color, national origin, gender identity, religion, num, comes from Hercules, of ancient mythological fame, and giant hogweed is age, disability, political beliefs, sexual orien- aptly described as robust. tation, marital status, family status, height, weight or veteran status. Issued in furtherance of Extension work in agriculture and home economics, acts of May 8 and June 20, 1914, in Additional resources cooperation with the U.S. Dept. of Agriculture. Thomas G. Coon, Extension director, Michigan • ohioline.osu.edu/anr-fact/hogweed.html State University, E. Lansing, MI 48824. • www.dec.ny.gov/docs/lands_forests_pdf/ghcontrol.pdf © Michigan State University • www.maine.gov/agriculture/pi/pestsurvey/pestinfo/documents/ghcontrolbrochure.pdf (4)