Horse thistle - Onopordum acaulon
EEffective: May 13, 2015
Taxonomic Position:
Asterales : Asteraceae
Pest Type:
Plants
Pest Code (NAPIS):
PBFCNDA
No manual – See Host Matrix |
These Approved Methods are appropriate for:
2024, 2023, 2022, 2021, 2020, 2019, 2018, 2017, 2016, 2015
Pest is vectored by:
This pest is is not known to be a vector and it is not vectored by any organism.
Survey
Approved Method(s):
Method |
Instructions |
NAPIS Survey Method |
Visual |
Collect suspect plants. |
3031 - General Visual Observation
|
Signs:
Found in pastures, roadsides, disturbed areas, irrigated vegetable crops, and cultivated land.
Plants develop a large rosette that may spread to cover an area up to 24 in or more in diameter. The numerous whitish-green leaves are densely covered in woolly hairs. They are deeply divided with numerous spiny, waxy lobes.
The flowers are borne in spherical flower heads 1.6 to 2.4 inches in diameter. Each head contains white or purple florets and is surrounded by sharp spines.
Seeds are gray or brown in color and about 0.16 in long. They are four-sided with a ridged seed coat and ~1 inch long pappus (parachute) of pale barbed hairs.