Giant Hogweed

 

Heracleum mantegazzianum, common name Giant Hogweed is a dangerous, noxious weed which has been found at many locations in Gogebic County Michigan and Iron County, Wisconsin.

A survey was conducted in order to mount a plan of action. Officials from the Michigan and Wisconsin Departments of Agriculture, in cooperation with the Michigan State University Extension, the Ottawa National Forest, will get together and develop a plan for eradication along with  USDA - (Animal and Plant Health Inspection Service which deals a lot with any of the  exotics or invasives)

Giant Hogweed Dangers

According to the U.S. Department of Agriculture, giant hogweed is both a public health and environmental hazard. It is a very harmful plant to people as well as dogs and other animals.

It's the clear, watery sap the plants exude which does its damage. . The Furocoumarins in giant hogweed sap, sensitizes the skin to ultraviolet radiation in sunlight. This causes a skin reaction known as phytophotodermatitis.

This can result in severe burns, long-lasting swelling, blisters and eruptions and painful dermatitis to the affected areas. The blisters can develop into purplish or blackened scars. 

The hyper-pigmentation in the affected area may remain for a year or more.

In the 1970s, many cases of poisoning were seen in Great Britain, where children played with the hollow stems of the plants as pea-shooters or telescopes. Parents should note that contact with the eyes can lead to temporary or permanent blindness. 
Click photos for larger image

Click for more pictures on burns  

from the King County, Washington website

Dealing With Hogweed 
Don't touch of handle plants using your bare hands! 
Don't allow children to play in hogweed. They may sometimes use the long hollow stems for  telescopes or peashooters. 
Don't transplant Giant Hogweed, plant its seeds or give away plants or seeds. 
Wash immediately with soap and water if hogweed sap contacts your skin. 
Report locations of and Giant Hogweed plants 

General Information
Giant Hogweed, a member of the parsley family,  Its tall, majestic appearance was probably responsible for its use in landscape settings, both in North America and Europe. 

The plant has escaped cultivation and has become established in rich, moist soils along roadsides, stream banks and waste ground. 

In Europe it is found in   England, Scotland, Scandinavia and Germany. In North America it grows in Ontario, British Columbia, Maine, Maryland, Connecticut, New York, Ohio, Pennsylvania, Michigan, Wisconsin, Iowa, Oregon and Washington.

Description

"How to Recognize Giant Hogweed "

Giant hogweed (Heracleum mantegazzianum)  is perennial or biennial herb. It is a member of the parsley or carrot family, Apiaceae (Umbelliferae). As its name indicates it is characterized by its size and may grow to 15  feet in height. Except for size, it closely resembles cow parsnip, Heracleum lanatum. 
Height Giant Hogweed grows to an imposing 15 feet in height
Stems and Leaf Stalks  2-4 inches in diameter, hollow and ridged, (raised bumps), with dark purple blotches and coarse, bristly, white hairs. The hairs are especially prominent at the base of the leaf stalk. In winter, dead stems may remain upright, providing an easy means of recognition. 
Leaves

Huge, sharp and unevenly lobed compound leaves (each leaf divided up into more than one leaflet)  approaching 5 feet long.  Each leaflet is deeply incised.
Fruit The fruit (containing the seed) is dry, flattened, oval,  about 3/8 inch long, and tan with brown lines 
Flowers The flowers resemble huge umbels of Queen Anne's Lace. Flowering occurs from mid-June to mid-July 
Each inflorescence may attain a diameter of 2-1/2 feet. The flowerets produce large elliptic dry fruits marked with brown swollen resin canals up to 1 mm in diameter.
Root Forked or branched tuberous taproot

Habitat

This weed can also form a dense canopy of leaves that displaces native plants. And because of its shallow roots it may increase the risk of soil erosion along waterways such as ponds, streams and irrigation ditches.
Giant hogweed is adaptable and may colonize a wide variety of habitats but is most common along roadsides, other rights-of-way, vacant lots, home landscapes, streams and rivers. 

Growth Stages

"Plants often do not flower until several years after germination"

Giant hogweed is a perennial which takes several years from germination to produce the first flowering stalk. It is believed to be monocarpic, dying after first flowering and seed set. Individual plants however, may produce additional crowns which continue to flower and set seed. Seed longevity is known to be greater than seven years. Reproduction is through seed and perennating buds formed on the crown and tuberous root stalk. Abundant seed production, a persistent root stalk, and vegetative reproduction from perennating buds are cited as reasons for its capability to colonize rapidly and expand populations.
Hogweed Seedling Seeds germinate from early spring throughout the growing season, after exposure to winder temperatures. Seedlings initiate the vegetative rosette pattern of growth the first season
Rosette of Leaves Leaf clusters sprout from over-wintering roots each year for 2-5 years until the plant flowers.
Flowering Stems


Plants bolt and flower in mid-summer after rosette plants accumulate enough energy reserves (from 2-5 years). 
Dead Stems
 After producing seeds in late summer, the plants die, leaving stems standing into winter. At this point seeds have been shed to germinate the following spring or in future years. 

Control Methods
Response to Herbicides 2,4-D, TBA, MCPA and dicamba will kill above ground parts but are reportedly not particularly effective on persistent rootstalks. 

Glyphosate (Roundup) is considered the most effective 
herbicide and should be used cautiously around desirable species since it is nonselective.

 Application during bud stage and while the plant is actively growing is recommended. 

 In wet areas" RodeoĆ" is possible but you should check with the state EPA to find which 
herbicides permitted.
Response to Cultural Methods Plants may be dug-out, but care should be taken to remove much of the root stalk. This can be difficult and unpleasant.
. 
Always wear protective clothing and avoid getting the sap on your skin. 

Mowing serves only to stimulate budding on the perennating root stalk, but might be successful if done consistently and persistently enough to starve the rootstalk.
Biocontrol Methods Cattle and pigs are cited as possible biocontrol agents. Both eat giant hogweed without apparent harm.

Whether any formal investigation for hytophagous insects in giant hogweed's native range has been 
conducted is unknown. 

What and What Not To Do

1. Contact someone from the your county extension office to report the location of the giant hogweed plants.   A professional will visit to the site to record information about the infestation and  advise you  how best to deal with the hogweed.

2. Avoid skin and eye contact with the sap of giant hogweed. Wear waterproof gloves, long sleeves and eye protection (glasses or goggles) if you plan to cut down or handle the plants.

3. Do not use a use a lawn mower,  "weed-whacker" or brush-cutter blade to cut giant hogweed,. Because the plant has a large perennial root system will send up new growth. Also, its sap could be splattered on you as stems are cut.

4. Do not burn as smoke air-born  irritants will burn your eyes and damage mucus membranes.

5. A long, sharp serrated knife is the best tool for cutting hogweed stalks or leaves.

6. Have several large plastic trash bags ready in preparation for disposing of hogweed flowers and seeds. Clear trash bags are best if you plan to “solarize” the contents (explained below), but dark bags are suitable as well. Double or triple bag the plant parts to prevent ripping of bags by cut stems.

7. Carefully cut off all inflorescences (flower heads) and place in trash bags. If seeds have formed, be especially careful to avoid shedding of seeds onto ground during the cutting and bagging process. It is best to do this prior to seed formation, because more mature seeds tend to shed easily. If seeds are shedding, contain them within as small an area as possible.

8. Seal trash bags tightly. If possible, place bags in a secure location where they will be exposed to direct sunlight to give flowers and seeds a heat treatment (solarization) for 1 week or more. This should help destroy seed viability. Then dispose of trash bags in the garbage.

9. You will also need to prevent giant hogweed plants from flowering again and to eliminate hogweed seedlings from developing further. This can be accomplished by carefully digging out the roots and allowing plants to thoroughly dry before disposal. However, digging up well-established hogweed plants or numerous seedlings is not an easy process.

10. If you only have a few plants in a small area, cut them down to ground level and cover the soil with black plastic. This will keep the plants from re-growing and prevent new giant hogweed seedlings from emerging. Keep an eye on the site next year to make sure that seedlings don't poke through the black plastic.

11. Another option for destroying the plants is to spray the leaves with a herbicide containing glyphosate as the active ingredient (“Roundup” or similar product). Glyphosate is a systemic herbicide that is absorbed by leaves and will move into the root to prevent regrowth the following year. Either apply a ready-to-use spray, or dilute a concentrated glyphosate product according to the label directions. Follow all the safety precautions on the label, and avoid contacting any desirable plants with the spray. Cover leaf surfaces thoroughly with spray droplets, but do not spray to the point at which liquid is dripping off the leaves. The best time to apply glyphosate is during the summer months when hogweed leaves are green and actively growing. Be patient: glyphosate is a slow-acting herbicide, so it may take up to 1 week before symptoms begin to appear as the plant eventually dies. Do not cut or dig up the plant until the top growth has died back. If the leaves remain green 2 weeks after initial treatment, spray them with glyphosate again.

12. Check the site and surrounding areas for the next several years for emergence of any hogweed seedlings or regrowth from previous year's plants. Reports suggest that giant hogweed seeds can remain viable in the soil for 7 years, so long-term monitoring is important.

The information provided is for educational purposes. The herbacide user is responsible for reading and following label directions. The label is the law. The user of this information assumes all risks for personal injury and property damage. Any references to commercial products, trade or brand names are for informational purposes only. No endorsement or approval of commercially available products in intended.

 

History
Giant hogweed is native to the Caucasus mountains (a region of Asia between the Black and Caspian seas, ) and  southwestern Asia. It has been introduced to the European continent, the United Kingdom, and Canada . Hogweed came to North America as early as 1917  as a garden curiosity.  Because of its size (8 to 15 feet in height) and imposing appearance, it was once used in arboretums and gardens. Because of its tenacious and invasive nature it soon becomes a pest within the ornamental garden and readily escapes. It has  naturalized in many of the places where it was first  introduced.

In 2004 local infestation was found and verified at five sites in Ironwood, including downtown near the intersection of McLeod Avenue and Lowell Street, and in the Norrie Location. Also, sites were discovered in Iron Belt, and Hurley, Wisconsin.

State officials are seeking cooperation in a process to eradicate a dangerous/non-native plant here on the Gogebic and Iron Ranges. To report a suspected infestation contact Joyce Price of Michigan State University Extension She may be reached at  906-932-1420.