Giant hogweed is a monocarpic perennial plant in the family of carrots called Apiaceae. It is also known as cartwheel flower, giant cow parsley, giant cow parsnip or hogsbane. Its scientific name is Heracleum mantegazzianum. This plant is a known invasive, and in this article we will talk about how to get rid of giant hogweed in your yard.
Its origin is the Caucasus region of Eurasia. Giant hogweed was introduced to other regions as an ornamental plant around the 19th century. It is now common in Britain, Canada, the U.S., and Western Europe. It is family to Persian hogweed and Sosnowsky’s hogweed which have also invaded most parts of Europe.
How to Identify giant hogweed
Giant hogweed typically grows to a height of around 2 to 5 meters (6 ft 7 in to 16 ft 5 in). The leaves are huge and a mature plant can produce leaves which are 1 to 1.5 meters wide (3 ft 3 in–4 ft 11 in). It has a bright green stem that is stout and has dark reddish-purple spots. The plant also has coarse white hairs which are usually dominant at the base of the leaf stalk.
Giant hogweed has hollow ridged stems which can grow up to a diameter of 10 centimeters (3.9 in). The dark red spots each surround a single hair. The plant can also form an umbrella-like top of a diameter about 100 centimeters (39 in). The flowers are symmetrical or bilaterally symmetrical.
The fruit produces seeds that are dry and flat. The seeds are usually one centimeter (0.39 in) in length and tan in color. Seeds are rounded around the top and in the ridges. A single plant can produce up to 20,000 seeds in a single season and they can easily fall ten meters from the parent plant. Other agents of dispersion include water and wind. These have the potential to transport the seeds even further. This makes it difficult to get rid of giant hogweed completely.
Giant hogweed leaves
The life cycle of giant hogweed
The life cycle of giant hogweed consists of four major phases. These are the pre-flowering phase, flowering phase, seeds phase, and dead stems phase.
The pre-flowering phase occurs during the formative stages of the plant. This phase always takes place in the first year of the plant. This is the time that the leaves sprout from the seed. It can also take place during the subsequent years but it is usually predominant in the first year. The flowering phase takes place after the initial phase. Giant hogweed flowers after several years of growth and development.
The flowers predominantly sprout during the mid-summer period. The next phase is the seeding phase. At this stage, the plant produces up to 20,000 seeds. The last phase is the dead stem phase where the plant dies leaving the seeds and dried stems standing.
Giant hogweed always takes 3 to 5 Years to grow a flower stalk in ideal conditions. The period may increase to 8 years if the conditions are not favorable to the plant. Giant hogweed flowers around June and July. In August, the plant starts producing seeds.
The seeds are usually dispersed by wind. They can also be dispersed over long distances by animals, water and even people. Giant hogweed seeds can stay viable for up to 5 years. The germination rate of the seeds is usually high, up to 90%. The other seeds are usually left dormant till the next germination period.
A single isolated seed can grow and give rise to a colony of the weed in an area.
Hogweed seeds
Natural habitat
Giant hogweed is mostly found in fields and forests. It likes plenty of sunlight and well-drained and moist soils. It grows in the area where there is plenty of rain and especially areas that receive rainfall of between 500mm to 2000 mm per annum. Giant hogweed is also rampant in rangelands, partially shaded areas and arable fields. The plant is also common in forests. In Germany and the Czech Republic, it has been found to mainly grow in abandoned grasslands and those that are not intensively taken care of.
Reports of giant hogweed in the US
Uses of giant hogweed
Long ago giant hogweed was initially used as a medicine to treat sores. The seeds were usually extracted and then boiled in oil to produce a concoction that would be applied to running sores and rashes. The seeds are also used to treat running ears.
The weed can also be used as food. Although, caution should be taken because other plants of this family are usually poisonous. They are similar in appearance and therefore someone can wrongfully choose a different plant which might have fatal consequences. The plant is believed to have a high content of vitamin C. it is usually eaten when it is still young. The young shoots are cut and boiled in salt water for about 15 minutes. The water is then drained and it is served with butter.
Destructive effects, and why giant hogweed is invasive
Giant hogweed contains a sap that is phototoxic. When skin comes into contact with the plant, it releases the sap which causes phytophotodermatitis. This is a condition where the skin cannot protect itself from the sunlight. This causes serious skin inflammations, blisters, and scars on the skin. When you come into contact with the plant, it is advised to stay out of sunlight for at least 48 hours.
The photosensitivity starts after 15 minutes and peaks after half an hour. This effect may last days. Authorities usually advise that people, especially children, should stay away from the weed. Protective gear is also recommended if one has to handle the plant. This also includes the eye. The parts of the body that come into contact with the plant sap must be washed thoroughly with soap and water to neutralize the effect of the sap.
Gardeners are especially wary of the plant because many have been severely affected by the plant. There have been cases where the plant has induced third-degree burns on unsuspecting gardeners who walked into it and they were harmed in a big way. The plant is also not easy on the eye since it can even lead to permanent blindness if the sap comes into contact with the eye.
Giant hogweed also destabilizes the ecological balance of the ecosystem by suppressing the growth of other native plants. This affects humans, livestock and wildlife. The size of the plant means that it seeps most of the nutrients in the soil, leaving the other plants around it without the essential nutrients and therefore they die off. This is an important reason to get rid of giant hogweed.
How to get rid of giant hogweed?
There are various control methods that have been found to be effective in the control of invasive giant hogweed. There are multiple methods to get rid of giant hogweed;
Mechanical control
These are the physical methods that are used to control and eliminate giant hogweed. These include root cutting, cutting the plant, mowing, covering the soil and even removing the seeds and flowers of the plant.
Root cutting
This is the physical uprooting or cutting of the roots of giant hogweed. The method is labor-intensive and requires many people to manage the work. It is effective for small area infestations in early spring. A spade with a sharp blade is used to cut the root of the plant around 15 centimeters (6 inch) below the ground level. Caution should be taken to avoid being in contact with the sap of the plant. The cut part is to be left out to decompose. One should come back after around two weeks to cut the missed weeds.
Hand pull
This is recommended when the plant is still young and the taproot is not well developed. One should wear protective gloves when touching the plant. It should be pulled gently because excessive force might break the plant and lead to partial removal of the roots.
Seed and flower removal
Using a pruner, one can easily cut the flowers of the plant. Avoid this method when the seeds are mature because the seeds will scatter and therefore give rise to other plants in the area. This method is usually effective if accompanied by other methods such as root cutting.
Plowing
The plant can also be controlled by plowing. Deep plowing especially ensures that the plant seeds do not germinate because the upper crust of the soil will be buried too deep. The plants which are cut during the plowing should be moved to other places to avoid regrowth of the plant. This method should be repeated for several seasons to achieve significant success in getting rid of giant hogweed.
Mowing
This method is effective in eradicating small hogweed plants. It is also advisable to mow several times in a season so as to completely destroy the plant. You should not mow plants with flowers or seeds because this will disperse the seeds. The mowing machine should be cleaned on-site so as to avoid spreading the hogweed seeds to other areas.
Herbicide control
The herbicides usually used to control giant hogweed are glyphosate and triclopyr. They can be used to control a single plant or a large area. These herbicides are usually absorbed by the leaves and travel down to the root system which inhibits the growth of the weed. Triclopyr only acts on broadleaf plants and therefore won’t harm the grass around it. On the other hand, glyphosate is a non-selective herbicide that destroys plants that it comes into contact with. Application of triclopyr in an area helps the grass to recolonize the area and therefore suppress the growth of the giant hogweed seedlings.
The herbicides should be used as per the manufacturer’s manual to get the intended result. The method should be applied severally during the season, to completely get rid of giant hogweed.
Grazing
Livestock, especially sheep, can be introduced to young giant hogweed plants. This can be done after mowing the plants. It allows regeneration of other plants in the area so that the livestock can have a mixed diet. Sheep are highly recommended because their bodies are covered with fur. The fur is resistant to the sap that the plant produces.
Conclusion
Giant hogweed is a noxious weed that is a threat to other living organisms. Its ability to cause serious skin inflammation poses a public health risk to people. Once it invades an ecosystem, it competes and eventually suppresses the other native plants in that ecosystem. Fortunately there are several methods to get rid of giant hogweed for good.
References
- https://www.cabi.org/isc/datasheet/26911
- https://www.mpi.govt.nz/dmsdocument/3664-national-pest-plant-accord-2012-manual
- https://www.dec.ny.gov/docs/lands_forests_pdf/ghcontrol.pdf
- https://www.sleloinvasives.org/about-invasives/target-species/giant-hogweed/
- https://www.nytimes.com/2018/07/02/us/giant-hogweed-nyt.html
