BIOLOGY: Adults emerge from soil in late May and are present through August. They are hairy and brown with white stripes. Adults are 4-6mm long. Eggs are laid in early to mid-summer. Females bore a hole into the seed head and deposit eggs. Eggs hatch in 3 days. Larvae feed on the seed head until larval development is complete (appx. 16 days). Pupation occurs in the seed head and lasts 8-13 days.
DESTRUCTIVE STAGE: Larvae and adult (seed head feeding)
IMPACT TO HOST: Larvae destroy seed heads. Adults feed on mature buds. Larvae can reduce seed production as much as 90-100% and reduce an infestation of yellow starthistle in 5 years.
REDISTRIBUTION: Adults can be collected in late June and early July using sweep nets or by picking adults off of plants. A typical release is 250 adults. E. villosus can be released on any size infestation from several meters to several miles.
BACKGROUND: Yellow starthistle was introduced from Europe. It grows well on dry sites in rangeland, roadsides, and waste areas. It can cause “Chewing disease” in horses that consume it.
OTHER COMMON NAMES:
DESCRIPTION: Yellow starthistle is a 2 to 3 foot tall winter annual with blue-green coloration. Rosette leaves are deeply lobed and could be confused with dandelion. Stems are winged and sparsely leaved. Flowers are yellow. Cream-colored thorns, ¼ to ¾ inch long, protrude from the flowering heads. Bloom is in early summer.
CONTROL: Several biocontrol agents have been tested, but availability is limited. Select herbicides offer fair to good control when applied between rosette and bloom stages. Tillage is effective. Contact your state or county weed specialist for specific, updated information.