spotted knapweed
Centaurea stoebe micranthos
Description and biology 6
- Plant: herbaceous biennial or perennial plant.
- Leaves: a basal rosette of deeply lobed leaves is produced the first year; rosette leaves are deeply lobed, stalked and about 8 in. long; stem leaves are alternate and may be slightly lobed or linear; leaves become smaller and less lobed toward the apex.
- Flowers, fruits and seeds: flowering stems are 2/3- 4 ft. tall and branched; flowers are produced early summer after the first year and resemble tiny pineapples topped with a showy ring of pink to light purple, highly dissected petals; the bract tips of the base (“pineapple”) are dark, giving the spotted look for which the plant is named.
- Spreads: by wind-dispersed seed.
- Look-alikes: other knapweeds and thistles including Canada thistle (Cirsium arvense) which occurs in similar habitats in the mid-Atlantic region.
Ecological threat in the united states 7
Spotted knapweed infests a variety of natural and semi-natural habitats including barrens, fields, forests, prairies, meadows, pastures, and rangelands. It outcompetes native plant species, reduces native plant and animal biodiversity, and decreases forage production for livestock and wildlife. Spotted knapweed may degrade soil and water resources by increasing erosion, surface runoff, and stream sedimentation. It has increased at an estimated rate of 27% per year since 1920 and has the potential to invade about half of all the rangeland (35 million acres) in Montana alone.
Prevention and control 8
The most cost effective management strategy for spotted knapweed is to prevent its spread to non-infested areas. Spread by seed can be minimized by avoiding travel through infested areas by: 1) cleaning footwear, clothing, backpacks, and other items after hiking through infested areas; 2) not grazing livestock when ripe seeds are present in the flower heads; and 3) using certified weed-free hay. Individual plants can be pulled by hand when the soil is moist as long as the entire crown and taproot are removed, using a shovel or weed-popper type tool if necessary. Control of spotted knapweed infestations is very difficult and may require large investment of time, labor and materials to remove using manual and mechanical means or repeated applications of herbicides often at higher rates.
History in the united states 9
Spotted knapweed was introduced to North America from Eurasia as a contaminant in alfalfa and possibly clover seed, and through discarded soil used as ship ballast. It was first recorded in Victoria, British Columbia in 1883 and spread further in domestic alfalfa seeds and hay before it was recognized as a serious problem.
Sources and Credits
- (c) Richard Spellenberg, some rights reserved (CC BY-NC-SA), https://calphotos.berkeley.edu/imgs/512x768/0000_0000/1114/1781.jpeg
- (c) Richard Spellenberg, some rights reserved (CC BY-NC-SA), https://calphotos.berkeley.edu/imgs/512x768/0000_0000/1114/1782.jpeg
- (c) Dean Wm. Taylor, some rights reserved (CC BY-NC-SA), https://calphotos.berkeley.edu/imgs/512x768/0000_0000/0706/0668.jpeg
- (c) Dean Wm. Taylor, some rights reserved (CC BY-NC-SA), https://calphotos.berkeley.edu/imgs/512x768/0000_0000/0706/0669.jpeg
- (c) Zoya Akulova, some rights reserved (CC BY-NC), https://calphotos.berkeley.edu/imgs/512x768/0000_0000/1008/0995.jpeg
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733871
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/23204942
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/22733872
- (c) Unknown, some rights reserved (CC BY-NC-SA), http://eol.org/data_objects/23204943
More Info
Range Map
iNat Map
| Flower color | purple |
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