bullweed n [Prob in all senses alluding to the large size of the plant. Connection with OED2 bull-weed “the knapweed (Centaurea nigra)” is unlikely; there is no evidence that this term has ever had any currency in the US except as an occasional book-name.]
1 = giant ragweed n. chiefly S Midl, esp TN Cf bullweed worm n, horseweed n 3, richweed n 5, wild hemp n 1
1828 Amer. Farmer 10.266 KY, There is a very large weed found in the corners of fences, and in other rich, untrodden spots, common among us, called the rich or bull weed, which all stock, but especially horses, are very fond of. 1868 S. Planter & Farmer 2.74 seVA, This growth consisted of iron weed or stick weed, of bull weed or wild hemp, and, below this, a rank growth of devil’s bit. 1890 Macon Republican (MO) 2 Oct [2]/3, Fences are hid with weeds and bushes, . . the low and the richest land covered with coarse weeds, black willow and bull weeds from twelve to fourteen feet high. 1915 Tulsa Democrat (OK) 15 Sept 14/2, Some of the fellows say Clarence White has on exhibition everything that grows in his community except bullweeds, cockelburs and sandburs. 1917 Hopkinsville Kentuckian (KY) 1 Sept 5/2, A huge weed of the richland or bull weed variety, grown on a branch of Saline creek, in Stewart county, Tenn, was brought to the Kentuckian office Wednesday. [It was] nearly three inches at the base and 12 feet high. 1932 Knoxville Jrl. (TN) 19 Dec 2/6, Cockleburs, Giant ragweed (bull weed), Jimson weeds, etc. denote good soils. 1940 Chattanooga Daily Times (TN) 13 Oct mag sec 6/3, Question—What is the correct name of the giant bullweed that grows profusely along the creek banks, and which in a green state is highly prized as food by horses and mules? . . Answer—This is great ragweed (Ambrosia trifida). 1940 in 1968 Haun Hawk’s Done Gone 15 eTN, But old bull weeds covered with ice don’t look any more like soldiers to me than sweet williams look like men. 1959 Decatur Daily (AL) 16 Aug sec A 11/3, Ever hear of bullweed worms? These are grubs that burrow in the pith of giant ragweeds, called bullweeds locally. 1967 DARE (Qu. S21, . . Weeds . . that are a trouble in gardens and fields) Inf TN6, Bullweed. 1979 Atlanta Jrl.–Constitution (GA) 15 Apr sec C 18/2, Perhaps the greatest bluegill bait that White ever put on his hook is the weed worm. The little critter makes its home in a knot on the stem of a drag [sic] weed, also known as a bull weed. 2012 in 2020 DARE File—Internet TN, I dont know if yall have bullweeds up younder, but we have lots of them and theirs a worm that lives inside of them.
2 An unidentified aquatic plant.
1915 WI Geol. & Nat. Hist. Surv. Bull. 45.109, At the water’s edge are found various kinds of aquatic plants, among them wild celery, white and yellow pond lilies, bull weeds and pickerel weeds. 1916 Elmira Star–Gaz. (NY) 28 July 3/2, I dug a large cake of ice out of the ice house . . , tied a big rock to it, and dropped the whole in between some of those lonely ‘bull weeds’ in that rocky cove north of Fish Point. 1949 McDavid Coll. swNY, Bull weeds ‘bulrushes.’ 1972 Palm Beach Post (W. Palm Beach FL) 30 Jan sec E 7/2, The weed-wing is also a surface spoon, which can be pulled through bullweeds, cattails, flooded needle grass and pepper grass. [2014 in 2020 DARE File—Internet Ontario Canada, Across the lake where the bull weeds are is where you can get muskie and perch and fishing for bass along the shorelines.] 2018 Ibid cnIA, I fish Clear Lake, Iowa quite a bit, my best crappie spots are in the middle of the bull weeds.
3 = horse nettle n 1. Cf bull nettle n 2
1904 St. Nicholas 32.77 cIL, At her feet, in company with the “tickle-grass,” the bull-nettle and nightshade grow side by side. To the Little Girl the berries of the latter two are the most beautiful of all the weeds. . . [T]he green-golden berries of the bullweed furnish oranges daily for the dolly‘s table.