Troublesome weeds along the roadside

Readers have asked what the tall, yellow-flowering plants are growing along the roadside in the same vicinity as poison hemlock. Though there are many yellow-flowering plants this time of year, the two most visible from the windshield would be yellow sweetclover and wild parsnip. A yellow-colored flower, biennial life cycle, and height of the flower stalk are the only things these two plant species have in common. Sweetclover is a member of the legume/bean family, and wild parsnip is a member of the carrot/parsley family. Sweetclover, Melilotus officinali (L.) Pall, is not even in the same genus as the true clovers (Trifolium ssp.) Its architecture and leaves are more like alfalfa. The sweet part of its name comes from the smell of the forage caused by the chemical coumarin, which can convert to a toxic anticoagulant, dicoumarin. Sweetclover is a nonnative plant brought in by early settlers from Europe as a hay and green manure crop. It is known as an excellent nectar source for honeybees. Plants complete their life cycle in two years. Flowers are produced the second year on the upper part of 3- to 5-foot-tall stems. Single flowers are formed along a central stalk that contain four petals (called a banner, keel, and two wings) that have a unique shape associated with plant flowers of the legume family. There is also a white-flowered type of sweetclover. Both types are on the Ohio Invasive Plants Council's invasive plant list because one sweetclover plant can produce over 100,000 seeds, which can remain viable for 30 years. In addition, during the second year of growth, sweetclover plants may out-compete native plants for sun, water and nutrients. Livestock producers who grow hay that contains sweetclover must make sure plants are properly dried and cured to prevent the production of dicoumarin. The toxin is produced when cut sweetclover plants become moldy and are then baled for hay, which may cause bleeding disease in animals. The other plant that may be found with a yellow flower along field edges and roadways at this time is wild parsnip, Pastinaca sativa L. Plant and leaf shape will be similar to poison hemlock, except that wild parsnip is generally somewhat shorter and the leaves have a more green-yellow coloration. The flowers are yellow, not white. Like other members of the carrot family, plants generally live for two years, growing as a rosette the first year and producing a 3- to 5-foot stem with flowers the second year. Clusters of flowers (called umbels) are arranged in a way that resembles small umbrellas. Individual flowers are small and have five petals. Wild parsnips are the same plants as those grown in gardens, except they have escaped the cultivated area. The edible tap root in the garden develops during the first year of growth. However, an individual should avoid harvesting these wild roots since they may confuse the plant with poison hemlock, which are toxic and may cause death. Parsnips also produce a toxin that may irritate the skin but not cause death. The sap or plant juices contain a chemical compound called furanocoumarin. This compound reacts to sunlight on the skin and may cause a chemical burn similar to sunburn called photodermatitis. The level of burn depends on the amount of the chemical on the skin. It may range from redness of skin to painful blisters (similar to a first- or second-degree sunburn). The burning effects may occur from a relatively short exposure to sunlight. The skin will become discolored (dark brown) and remain that way for over a year in some cases. People may inadvertently come in contact with parsnip sap as a result from walking among plants along the roadway, hunting for a lost golf ball or chasing an escaped pet. Other cases occur while mowing or using weed trimmers. The key to protection is not exposing bare skin to the sap. Thus, when working in areas of wild parsnips (or any parsnip): • Keep arms and legs covered with long sleeves and pants. • Work with the plant on cloudy days and wash your skin immediately if contact has been made with plant sap. • Wear eye/face protection along with a long-sleeved shirt, long pants and gloves when mowing or using a weed trimmer. • Be careful not to touch your face or bare skin, since hands may have come in contact with contaminated clothing. • Wash skin immediately if skin comes in contact with plant sap. • Protect from sunlight skin that may have been in contact with plant juices for 48 hours. Animals and livestock fur or hide will protect them, but they are also susceptible if the plant juices come in contact with bare skin. Individuals may also come in contact with the sap if animals have been running through a parsnip area and get sap or juices on their fur. Lentz is Extension educator for agriculture and natural resources for Ohio State University Extension-Hancock County.