This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Native. Biennial. Propagates by seeds.
Time of bloom: July to October.
Seed-time: August to November.
Range: Newfoundland to Manitoba, southward to the Carolinas, Tennessee, and Iowa. Habitat: Meadows, pastures, roadsides, and waste places.
A conspicuous weed, its stem three to twelve feet tall, full of bitter milky juice, stout, round, smooth, very leafy up to the large, rather dense, compound panicle. Leaves six inches to a foot long, two to six inches wide, deeply and irregularly lobed, sharply toothed, smooth above but sometimes slightly hairy on the veins beneath, those on the stem sessile, clasping, and auriculate, the lower ones narrowed to winged petioles. Heads very small, about a quarter-inch broad, the rays usually pale blue but sometimes cream-colored. Achenes slightly flattened, very short-beaked, the pappus tawny brown.
Means of control the same as for the preceding species.