By Matt Reese
While helping her father cut back the spent leaves of the daffodils growing along the creek this spring, a little girl was sent to the house to seek out Mommy regarding some significant blisters on her hand.
“It looked like her hand had been attacked by bees. Immediately she had blisters on her hand. It was turning red and she said it was stinging,” said Amy Laine, who lives in Franklin County. “My husband said there were no bees out there and that she must have touched something. It looked like she had seven or eight bee stings on her tiny little hand and it happened so fast.”
Some ice, Benadryl and a shower seemed to help sooth the blisters, but the mystery remained: what caused them? A couple of weeks later, Laine was watching the news and a story about giant hogweed growing in Virginia caught her attention. The large, toxic plant made national headlines after horticulturists from Virginia Tech officially identified the first known hogweeds growing wild in Virginia in June. The finding was interesting, but it is the toxicity of the plant that generated the headlines.
“Giant hogweed’s greatest danger is the effect its sap has on humans. Furocoumarins in the sap can cause a skin reaction known as phyto-photodermatitis. This causes the skin to be highly sensitive to ultraviolet light,” wrote David L. Marrison and David J. Goerig in an Ohio State University Extension Fact Sheet on giant hogweed in 2016. “Swelling and blistering of the skin occurs and may lead to permanent scarring. Contact with the eyes can cause temporary and sometimes permanent blindness.”
“I wouldn’t have known except I saw the news story about it. Unfortunately we do have this unwanted weed. I thought it might be Queen Anne’s Lace but unfortunately when we took a closer look it definitely has the appearance of giant hogweed. It is growing right by a culvert and a stream and this weed is right at the side of the creek by the roadside. It is about five feet in height and the stalk of it is pretty thick with some purple striations and it has some pretty wild leaves. At the top is that white umbrella flower,” she said. “We had the start of this foliage last year but it never flowered. It just flowered in the last week [late June]. I am sitting on my porch and I can see it. I called the Franklin County Extension office and they sent a couple of documents, including a Fact Sheet. This weed is definitely not something I am going to touching or removing myself.”
According to the Extension Fact Sheet, “Giant hogweed is an herbaceous dicotyledonous plant that is classified as having a biennial life cycle. It is a member of the Apiaceae (Umbelliferae) family of plants, commonly known as the Carrot or Parsley family. It can live for several years but once it flowers and bears fruit it dies. Giant hogweed is hardy to zone 3 and prefers full sun and moist, well-drained soil. Giant hogweed can be identified by its large compound umbel of white flowers, large, deeply incised leaves, and prominent white hairs and purple blotches on its stems.”
Marrison and Goerig point out that “giant hogweed (Heracleum mantegazzianum) is on the federal and Ohio noxious weed lists making it unlawful to propagate, sell or transport. It has been included on these lists because of its ability to crowd out native plants and because of its potential human health hazard.”
The plant can produce 20,000 seeds and spreads quickly when not managed. It was originally used in ornamental gardens but now can be found growing in ditches, stream banks and fence lines. Removing and controlling the weed should be done with caution, wearing protective clothing and eyewear, Marrison and Goerig advise.
“Control of giant hogweed usually includes such practices as digging, mowing, cutting, removal of umbels, grazing, and herbicide application. The control strategy, or strategies, selected will be dependent on the area covered by the population, accessibility, and plant density. Because giant hogweed is a moderate seed producer, continuous management to prevent seed production is extremely beneficial. Most research indicates that five years of intensive management is required to attempt to eradicate it. The goal of mechanical or cultural control is to deplete the energy reserves of the plant’s root system and eliminate seed production. Chemical control is the most common control strategy utilized. Research trials have demonstrated giant hogweed can be effectively controlled using herbicides; however, multiple applications are usually necessary,” they wrote. “Triclopyr and glyphosate (Roundup and many other products) have both been shown to be effective due to their systemic activity. The minimum glyphosate rate should be 0.75 pounds of acid equivalent per acre, but the exact rate still needs to be determined through research trials. Other products such as 2,4-D, TBA, MCPA, and dicamba may control the aboveground portion of the plant but are relatively ineffective at killing the root stock.”
For much more on giant hogweed, see the Extension fact sheet at https://ohioline.osu.edu/factsheet/anr-35.