Yellow starthistle (Centaurea solstitialis)
Keys to ID:
- Winged stems
- Flowers have yellow rays and disk with stiff spines at flower base
- Leaves are blue-green
Identification:
- Lifecycle: Winter annual
- Growth form: Forb
- Flowers: yellow flower heads located singly at the ends of branches. Flower heads are distinguished by sharp, straw-colored thorns, which are up to 0.75 inches (2 cm) long. Yellow starthistle bolts in late spring, and flowers June through August.
- Seeds/Fruit: two types of seed: plumed and plumeless.
- Leaves: Basal leaves are deeply lobed while the upper leaves are entire and sharply pointed.
- Stems: Mature plants are 2 to 3 feet (0.75 to 1 m) tall and have rigid, branching, winged stems that are covered with cottony hairs.
- Roots: Taproot
- Propagation: Seedlings usually emerge in the fall, form rosettes, and begin growing a taproot. Root growth continues throughout the winter. It reproduces entirely by seeds that may remain viable for several years. Plumed seeds are dispersed by wind shortly after maturity. Plumeless seeds remain in the seedhead until it disintegrates in the fall or winter.
Control:
Mech: Hand pull, making certain to pull all the roots. Remove all parts of plant including dry skeletons. Timing of mowing is critical; early season mowing can increase starthistle density. It is best to mow when plants had just started to bloom to reduce flower head density and mow again to remove re-growth.
Cautions:
Be careful of spines, as they are very sharp and can get imbedded under your skin. Make sure you do not spread seeds from this plant after entering infested areas.