What are those yellow flowered plants in ditches and wetlands?
It's probably perennial sowthistle, says Darrell Deneke, SDSU Extension integrated pest management coordinator.
There has been a lot more sowthistle this year than normal. But it's not a new weed. Sowthistle has been on South Dakota statewide noxious list since 1956. It was considered one of the major noxious problems and would be number one or two on the most acres in the state through the late 1950s and into the 1960s, he says.
Perennial sowthistle is a native of western Asia and Europe. It is common in cultivated areas, rights-of-way, meadows, and lowland grasslands. Perennial sowthistle can grow anywhere from 4 to 6 feet tall, reproducing by seeds and horizontal roots. Rhizomes and horizontal underground roots measure about half an inch in diameter, usually 2 to 5 inches below the soil surface, and can grow 4 feet or more in a single growing season.
Perennial sowthistle can survive very cold winter temperatures due to the fact that the roots can overwinter and survive temperatures to 0 degrees Fahrenheit. The roots are white and brittle, widely spreading, penetrating five to ten feet into the soil profile. This weed can produce new plants from small root pieces.
When broken, both the leaves and stem exude bitter, milky latex like juice. The leaves are alternate, and lower leaves are deeply lobed, while the upper leaves clasp the stem. The leaves are similar to dandelion leaves except with teeth ending in small weak prickles. Flowers are bright yellow up to 2 inches wide and are dandelion or daisy-like in appearance, blooming from June through August. Seeds are tufted and can be dispersed by the wind.
There are other species of sow thistle in the state. They are annuals or winter annuals and it can be difficult to make a distinction between the perennial and annual sow thistles. This is because all three versions are tall weeds with yellow, dandelion-like flowers with leaves and stems that produce a milky sap. Seedlings and mature plants of all the species are practically indistinguishable, and may be difficult to tell apart without examining the root system. The more common of these species include annual sow thistle and spiny sow thistle. The annual sowthistles are not on the state noxious weed list.
Control options for perennial sowthistle include herbicides, mowing or tillage.
Source: SDSU Extension