Dalmatian toadflax is a member of the snapdragon family and thus easily recognizable by the bright yellow flowers, which have swollen corolla tubes that flare into two “lips” and long spur. The flowers are 1 to 1.5 inches long with many flowers on a raceme. The plants have an extensive creeping rhizomatous root system that spreads like leafy spurge. Dalmatian toadflax has broad, heart-shaped leaves that clasp a woody stem.
The plants begin regrowth from the roots as soon as the soil warms in early spring. Toadflax flowers from late June through August in North Dakota and single plants may produce more than 500,000 seeds that are dispersed by wind, rain, wildlife, and movement of forage and livestock. The seed is disk-shaped, 0.08 inch in diameter and dark brown to black, and often have irregular papery wings. Seed dispersal begins a few weeks after flowering and continues into winter. The roots of a single plant can extend 10 feet and give rise to daughter plants every few inches.
The stem-boring weevil Mecinus janthiniformis has been the most successful and can reduce Dalmatian toadflax stands relatively quickly. M. janthiniformis larvae mine in Dalmatian toadflax stems, which slowly causes the plants to wilt and die.
From Lym and Travnicek, 2015, NDSU Circ. W-1411.
For full description, growth habits, and other control options: Identification and Control of Noxious and Troublesome Weeds in North Dakota