Replacement of perennial grasses with non-native annual grasses in California’s Central Valley grasslands and foothills has increased deep soil water availability. Yellow starthistle (Centaurea solstitialis), a deep-rooted invasive thistle, can use this water to invade annual grasslands. Native perennial bunchgrasses, such as Purple needlegrass (Nassella pulchra), also use deep soil water, so t...

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Proving allelopathic chemical interference is a daunting endeavor, in that production and movement of a phytotoxin from a donor plant to a receiving plant must be demonstrated in the substrate in which the plants grow, which is usually a complex soil matrix. The soil levels or soil flux levels of the compound generated by the donor must be proven to be sufficient to adversely affect the receivi...

A Russian knapweed (Acroptilon repens) shoot culture system, initiated from shoot tip culture, was used to generate a source of host plant tissue for the rearing of the nematode Subanguina picridis, a biocontrol agent for Russian knapweed. Young shoots growing on solid B5G medium in petri dishes developed galls on leaves, petioles, and shoot tips 7 days after release of 50 nematodes onto the su...

BACKGROUND Agri-environment schemes play an increasingly important role for the conservation of rare plants in intensively managed agricultural landscapes. However, little is known about their effects on gene flow via pollen dispersal between populations of these species. METHODOLOGY/PRINCIPAL FINDINGS In a 2-year experiment, we observed effective pollen dispersal from source populations of C...

Polyploidy is often assumed to increase the spread and thus the success of alien plant species, but few empirical studies exist. We tested this hypothesis with Centaurea maculosa Lam., a species native to Europe and introduced into North America approximately 120 years ago where it became highly invasive. We analyzed the ploidy level of more than 2000 plants from 93 native and 48 invasive C. ma...

Russian knapweed (Rhaponticum repens) is a rangeland weed pest in the western United States. One candidate fungus for biological control of R. repens is Puccinia acroptili, which causes a rust disease. Understanding the life cycle of candidate rust fungi for weed biological control is an essential component in risk assessments and evaluations, and for P. acroptili such was unknown. For this rea...

The threat posed by exotic organisms to native systems has led to extensive research on exotic invaders, yet management of invasives has progressed relatively slowly. This is partly due to poor understanding of how exotic species management influences native organisms. To address this shortfall, we experimentally evaluated the efficacy of an invasives management tool for restoring native deer m...

Centaurea corymbosa (Asteraceae) is endemic to a small area (< or = 3 km2), and < 500 individuals reproduce in any given year. Nevertheless, enzyme polymorphism was found within and among the six local extant populations, the most distant at 2.3 km. Levels of gene flow among populations and seed and pollen dispersal data indicated very low dispersal capacity. Rarity of long distance dispersal e...