The Response of Yellow Starthistle (Centaurea solstitialis), Spotted Knapweed (Centaurea maculosa), and Meadow Hawkweed (Hieracium caespitosum) to Imazapic1

2003 ◽  
Vol 17 (1) ◽  
pp. 94-101 ◽  
Author(s):  
SANDRA L. SHINN ◽  
DONALD C. THILL
Keyword(s):  
Centaurea Maculosa ◽  
Centaurea Solstitialis ◽  
Spotted Knapweed ◽  
Yellow Starthistle ◽  
Meadow Hawkweed

scholarly journals Factors Affecting Infection of Yellow Starthistle (Centaurea solstitialis) by Synchytrium solstitiale, Causal Agent of False Rust Disease

Plant Disease ◽  
2006 ◽  
Vol 90 (4) ◽  
pp. 425-428 ◽  
Author(s):  
T. L. Widmer ◽  
F. Guermache
Keyword(s):  
United States ◽  
Classical Biological Control ◽  
The United States ◽  
Carthamus Tinctorius ◽  
Centaurea Solstitialis ◽  
Yellow Starthistle ◽  
Rust Disease ◽  
Invasive Weed ◽  
Factors Affecting ◽  
Centaurea Calcitrapa

Yellow starthistle (Centaurea solstitialis) is an annual invasive weed in the United States with Mediterranean origins. The expense of chemical control and the vast area of invasion make this weed an appropriate target for classical biological control. Observations of a field site in southern France revealed small orange galls on the leaves of yellow starthistle seedlings caused by the fungus Synchytrium solstitiale. Inoculation of yellow starthistle seedlings with a suspension of zoospores released from infected tissue resulted in infection. Ten days after inoculation, typical orange galls appeared on the exposed tissue. Preliminary host range testing showed up to 100% infection of C. solstitialis seedlings from both France and the United States and infection of Carthamus tinctorius, Centaurea americana, C. diffusa, C. rothrockii, C. squarrosa, and Helianthus annuus seedlings. No symptoms were observed on seedlings of Centaurea calcitrapa, C. maculosa, C. sulfurea, Cirsium californica, C. occidentale, Cynera cardunculus, and Taraxacum officinale. Zoospores were released in a pH range between 4.45 and 8.25 and optimally at temperatures between 5 and 15°C. Infection of yellow starthistle seedlings occurred after a minimum 1-h exposure to a zoospore suspension at 20°C.

Distribution of Urophora affinis and U. quadrifasciata, Two Flies Introduced for Biological Control of Spotted Knapweed (Centaurea maculosa) in Montana

Weed Science ◽  
1987 ◽  
Vol 35 (2) ◽  
pp. 145-148 ◽  
Author(s):  
Jim M. Story ◽  
Robert M. Nowierski ◽  
Keith W. Boggs
Keyword(s):  
United States ◽  
Biological Control ◽  
North America ◽  
Positive Relationship ◽  
The United States ◽  
Centaurea Maculosa ◽  
Spotted Knapweed ◽  
Seed Head ◽  
Strong Positive Relationship ◽  
Southeasterly Direction

A survey was conducted at 88 sites in Montana in 1984 and 1985 to determine the distribution of Urophora affinis Frauenfeld and U. quadrifasciata (Meigen), two seed head flies released on spotted knapweed (Centaurea maculosa Lam. # CENMA) in North America. U. affinis, released in Montana during 1973 to 1977, was found at 40 of the 88 sites. The fly was concentrated within a short radius (about 5 to 8 km) of release sites, even at sites having well-established populations. U. quadrifasciata, released in British Columbia in 1972, but not in the United States, was found at 84 sites. The data suggest that the fly entered the state in the northwest corner and dispersed in a southeasterly direction. There was a strong positive relationship between mean number of galls per seed head and percent infestation for both fly species.

Cnicin concentrations in Centaurea maculosa, spotted knapweed

1987 ◽  
Vol 15 (3) ◽  
pp. 313-320 ◽  
Author(s):  
Laura J. Locken ◽  
Rick G. Kelsey
Keyword(s):  
Centaurea Maculosa ◽  
Spotted Knapweed
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