The giant hogweed plant (Heracleum mantegazzianum) is an Apiaceae (carrot) family herb. There are 148 species in the Heracleum genus, but the giant hogweed plant is one of the two most common in North America. The cow parsnip, which is frequently confused with the giant hogweed, is another common species.
The sap of the giant hogweed is phytotoxic, and contact with the skin causes phytophotodermatitis. Phytophotodermatitis is a skin condition in which the skin is unable to protect itself from the sun’s rays. The skin loses its defenses and can sustain third-degree sunburns, blisters, infection, and scarring.
Not to mention that the giant hogweed can reach heights of 15 feet.
It goes without saying that having this plant anywhere near your perfectly manicured lawn is a bad, bad thing. So, let’s look at how to recognize this toxic plant and what you can do to control and prevent it from appearing on your lawn.
Giant hogweed is also known by a few other names – cartwheel flower, giant cow parsley, giant cow parsnip, and hogsbane
It typically stands between 6 and 15 feet tall. Some specimens discovered growing in ideal conditions were nearly 18 feet tall.
When mature, the hogsbane’s massive leaves can grow up to 5 feet wide. The leaves are deeply lobed and have irregular, sharp cuts. Each leaf has three lobes, and each stem has multiple leaves. Each leaf’s pronounced ribs are covered in fine hairs.
The green leaves are darker in color than the stems. The lower surface of the leaves is hairless but a little rough to the touch.
The hollow stems are strong and bright green. They have purplish-red spots that surround each single coarse white hair. The ridged stems are typically 1 to 3 inches in diameter.
Under ideal growing conditions, stems as large as 5 inches across can be produced. If the conditions are favorable and the primary stem is large enough to support them, the stems can grow to be as tall as 15 feet.
The flat top of the umbrella-shaped inflorescence can grow to be 4 feet across. The white to greenish-white flowers grow in clusters and resemble Queen Anne’s lace in size (Dacus carota). Flowers can be radially or laterally symmetrical.
Schizocarps are the fruits produced by the giant hogweed. Each schizocarp contains flattened and dried-out seeds. Tan seeds are oblong and grow to be about 0.5 inches long.
Hogsbane was foolishly introduced to North America as an ornamental plant. It is now classified as an invasive and noxious weed.
Giant hogweed is somewhat tolerant of partial shade but thrives in full sun. This herbaceous perennial flowering plant prefers moist conditions. As a result, it is frequently found alongside streams and drainage ditches. It is also found in and around woodlands, roadside ditches, blighted lots, and your healthy lawn.
Giant Hogweed Control Methods
Let’s look at some of the different control methods for hogsbane infestations.
Manual and Mechanical Methods
Root cutting is the only manual method that will get rid of this noxious after just one round of treatment. Only use root cutting for single giant hogweed plants or small infestations.
To complete this task successfully, you must cut the taproot at least 6 inches below the soil’s surface. Cut the taproot with a spade or a garden hoe.
To prevent the taproot from returning in larger specimens, cut it as deep as 12 inches. Root cutting is an extremely effective control method, but it is also extremely time-consuming.
Mowing and Trimming
Mowing and trimming can be effective if done consistently over time. With each new mowing or trimming session, you weaken the rootstalk by depleting its nutrient stores in order for it to regrow. However, the giant hogweed will continue to be a problem for some time.
Regardless of whether you use a manual or mechanical method, you should take care of the problem before it spreads.
Cultural and Biological Control Methods
Grazing animals on your property is not a practical option for most homeowners. If you are the type of landowner who can put animals out to pasture, grazing sheep and rooting pigs are effective methods of cultural control. Cows find it less appealing than sheep and goats.
Unfortunately, no known biocontrol insects exist to control the giant hogweed plant.
Chemical Control Methods
Glyphosate is the most commonly used chemical herbicide to control it. Glyphosate is a highly effective post-emergent chemical treatment that should be used during the summer. The giant hogweed is still in its bud stage during this time and is growing quickly, healthily, and robustly.
When spraying the giant hogweed, make sure to cover the entire surface area of the leaves with water until they are wet but not dripping. If the leaves are still green after 2 weeks, another round of herbicide is required.
Whatever you do, avoid cutting or digging up the giant hogweed until the top cover has died off. Always wear personal protective equipment over any exposed skin when working with this toxic plant.