Keeping this species in check at this time will prevent the spread of the species. The banks of t... more Keeping this species in check at this time will prevent the spread of the species. The banks of the Stanislaus River are prime habitat for this species and may be a focal point for control. Carduus pycnocephalus (Italian Thistle) Cal-IPC List B. Carduus pycnocephalus is an annual thistle, introduced from the Mediterranean with reports of its occurrence as early as 1912 (Bossard et al. 2000). It is widespread in the grasslands and oak woodlands within the study area. It is considered less invasive than some other species of thistle but once established it can come to dominate a site. It is the most abundant of the exotic thistles within the study area. It was found in 30 associations, ranging in absolute cover from <1% to as high as 40%. Control may center on identifying those areas of heaviest infestation. Research of the literature seems to indicate that mechanical control and grazing are the most effective methods. Treatment, however, requires being persistent over a period of several years. Centaurea melitensis (Maltese Star-thistle) Cal-IPC List B Centaurea melitensis is an annual thistle, first introduced to California during the Spanish mission period. Dense infestations can displace native plants and animals (Bossard et al. 2000). Though placed on Cal-IPC List B, it is noted that this species may be more widespread than realized. It is often mistaken for C. solstitialis. The plant can be toxic to horses if ingested over long periods. Little work has focused on the control of C. melitensis with more focus given to C. solstitialis. With similar life-forms and habit, control methods used for C. solstitialis may be effective on C. melitensis (Bossard et al. 2000). Control may center on identifying those areas of heaviest infestation. It is the second most abundant of the exotic thistle species. It occurs in 24 associations ranging in absolute cover from <1% to as high as 20%. Centaurea solstitialis (Yellow Star-thistle) Cal-IPC-List A-2 Centaurea solstitialis is considered one of the most noxious weeds in the state. It can form dense impenetrable stands diminishing the quality of rangelands and displacing other vegetation. It has spread rapidly since the mid-1900s and has come to infest 15-20 million acres throughout California. It is believed to have begun invading the Sierra foothills in the 1930s and 1940s (The Nature Conservancy 2004). Like C. melitensis, the plant is toxic to horses. 5000-Deciduous Shrubland 5400-Winter Rain Drought Deciduous Shrubland 5401-Poison Oak Alliance 5500-Seasonally Flooded Deciduous Shrubland 5501-Mixed Riparian Shrub Mapping Unit (including Salix spp., Calycanthus occidentalis, Rhamnus tomentella, etc) 6000-Perennial Herbaceous (Graminoid-Forbs) 6100-Bunch Forming Grasses 6101-Serpentine Native Wet Perennial Grassland (Hordeum brachyantherum, Carex spp., Juncus spp.
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