This section is from the book "A Manual Of Weeds", by Ada E. Georgia. Also available from Amazon: A Manual Of Weeds.
Introduced. Annual. Propagates by seeds.
Time of bloom: June to August.
Seed-time: July to September.
Range: Illinois, Kentucky, Tennessee, North Carolina, and New Jersey. Habitat: Hemp and tobacco fields; parasitic on tomatoes in New Jersey truck gardens.
Broom-rapes are parasites, or robber plants, living directly on their neighbors by attaching strong haustoria, or suckers, to their roots, penetrating the tissues, and absorbing the food materials gathered and assimilated by the host plants for their own development. This species was brought to this country in imported hemp and tobacco seed, and in like manner its range here is being extended.
A Broom-rape seedling appears like a mere light-colored, nearly transparent thread, without root or any green part, having power to push its way into the soil but not to draw any sustenance from it. If a suitable host is not found soon after germinating, it shrivels and dies; but if the downward-boring tip comes in contact with the host adapted to it, in this case a plant of tobacco or hemp, it develops a club-shaped attachment covered with little pegs, or suckers, which penetrate and seem to become a part of the host plant's root, from which thereafter its life is drawn. At the point of juncture a bud is formed and a stem arises, six to fifteen inches tall, rather fleshy at base, dividing into several slender branches, the whole plant brownish yellow in color, with a few scattered scales instead of leaves. The flowers are in spikes terminating the branches, sessile or on very short pedicels, subtended by three or fewer small, scale-like bracts; each blossom has a persistent, four-lobed calyx and an irregular, two-lipped corolla about a half-inch long, with yellow tube and pale bluish lips, the upper one two-cleft, the lower one more spreading and three-parted; four stamens, inserted on the tube and included; ovary one-celled, the style very long, with two-lipped stigma. Capsule bluntly ovoid, one-celled, two-valved, containing an immense number of the most minute seeds, which are widely sown by the winds and, though so small, are very long-lived, having been known to survive in the soil for as many as thirteen years.
If the infestation is new, it will pay to pull or grub out and destroy the stalks as fast as they attain to flowering size, in order to prevent any development and distribution of seed. Burn all stems of tobacco or hemp from infested fields and cultivate some other crops on that ground for several seasons.