Every year at the UConn Home & Garden Education there are a few topic of interest that we get a lot of calls about. Several years ago we fielded a lot of calls about the drought situation in Connecticut that occupied many people’s thoughts in 2016. In fact, that encompassed two years as we started to feel the effects of it in 2015. On the tail end of the drought, and perhaps in part because of it, many parts of the state were visited with an infestation of gypsy moth caterpillars. When we have a wet spring the fungus Entomophaga maimaiga, a natural control of the gypsy moth caterpillar, can flourish. The fungus overwinters as spores in leaf litter and in the soil. It then reactivates in the spring when there is sufficient rainfall. Although we were receiving an adequate amount of rain by 2017 it happened to occur a bit late for the fungus to be fully effective against the voraciously feeding caterpillars. So the summers of 2016 and 2017 were dedicated to answering many questions about the gypsy moth caterpillars and the damage that they wreaked.

As those two events have wound down a new concern arose for many of our clients. Thanks in part to press releases and an interview that aired on NBC CT in June the giant hogweed, Heracleum mantegazzianum, (below images) jumped to the front of the queue. The Connecticut Invasive Plant Working Group (CIPWG) issued a warning about this invasive species which was first spotted in Connecticut in 2001. Most of the populations of giant hogweed are under control and none of the reported sightings in 2018 were positive.

There are many look-a-like plants and it is those species that we are asked to identify. Starting in early-June calls and emails began to come in to identify large herbaceous perennials that were striking fear into Connecticut residents. This is in part due to the pretty noxious nature of the giant hogweed sap. Within 24-48 hours after skin has been in contact with the sap painful blisters may appear in individuals that are sensitive to it. Three things need to be present for the reaction known as phytophotodermatitis to occur. First, direct contact between the skin and the sap. Second, the skin must be moist as from perspiration, for example. Third, the contaminated area must be exposed to sunlight. If you are working in an area that contains giant hogweed it is easy to imagine that all of the criteria could be easily met.

Before attempting to remove giant hogweed from an area the first step should be positively identifying it. As I mentioned earlier, there have not been any confirmed sightings in Connecticut yet this year. It may be that the suspected plant is one of the following instead.

The first plant that is most commonly mistaken for giant hogweed is fellow member of the Heracleum genus: cow parsnip, Heracleum maximum, (images below). Unlike giant hogweed which was introduced to the United States 100 years ago from the Caucasus region of Central Asia, cow parsnip is native to North America. A tall herbaceous perennial that can reach up to 10 feet in the shade, nowhere near the 18 feet possible height of the giant hogweed, cow parsnip bears its flowers in in the flat-topped or rounded umbels that are characteristic of other members of the carrot family, Apiacea. Both species have compound deeply-lobed, toothed leaves but the cow parsnip lacks the red veining and leaf stalks common to giant hogweed. Cow parsnip also contains chemicals that cause phytophotodermatitis.

The next most common look-a-like is angelica, (below images). A first cousin once-removed, it shares its family, Apiaceae, with the giant hogweed and cow parsnip but is in the genus Angelica. Angelica grows 3-9 feet tall and also has large umbel flower heads. The compound leaves of angelica are what distinguish it from giant hogweed as they are bipinnate, meaning that they are compound leaves in which the leaflets are also compound (think honey locust leaves). Often used as a medicinal herb, angelica is the least toxic of the hogweed look-a-likes although it may still cause a skin reaction.

Queen Anne’s lace, Daucus carota, (below images) takes compound leaves one step further to tripinnate, having pinnately compound leaves that are bipinnate. The more levels of pinnation, the more delicate the overall effect. The airy-looking leaves of D. carota are what give it the ‘lace’ part of its name and are similar to its subspecies, the domestic carrot. Queen Anne’s lace has an umbellate flower head atop a much slimmer stem than giant hogweed, cow parsnip, or angelica. The sap from the leaves and stems can cause a phytophotodermatitis reaction although the flowers are used to make jelly similar to the yarrow jelly from our June 26th blog post.

The native Lactuca species includes wild lettuce (Lactuca Canadensis),

prickly lettuce (L. serriola), hairy lettuce (L. hirsute), and the blue lettuces (l. biennis, L. floridana, L. pulchella, L. villosa).

These tall plants start out from a basal rosette of leaves and can grow to 7 feet tall with large alternating broad leaves.  They have pale blue insignificant flowers compared to the dense clustered heads of the previous plants.

Finally, giant ragweed, Ambrosia trifida, has also made a plant identification appearance.  This 6-foot tall annual herb is a noxious weed that has become invasive in other parts of the world as it out competes native species in much the same way that the giant hogweed has here.

As plants and seeds have spread across the globe through human, animal, mechanical, or water means many species have landed in non-native locations and taken root there. If you are a fan of podcasts, check out the Infinite Monkey Cage’s Invasion episode where scientists and comedians take a look at the problems caused by alien (plant) invasions.

Susan Pelton, UConn Home & Garden Education Center

All images by CIPWG and UConn