Demography of meadow and spotted Knapweed populations in New York

Authors: Milbrath, Lindsey; Biazzo, Jeromy

Submitted to: Northeastern Naturalist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/28/2020
Publication Date: 7/27/2020
Citation: Milbrath, L.R., Biazzo, J. 2020. Demography of meadow and spotted Knapweed populations in New York. Northeastern Naturalist. 27(3):485-501. https://doi.org/10.1656/045.027.0309.
DOI: https://doi.org/10.1656/045.027.0309

Interpretive Summary: Spotted and meadow knapweed are emerging invasive weeds of pastures and grasslands in northeastern North America. Gaps remain in our knowledge of how populations of these plants change over time and thus how we might best control them using biological control or other management tools. As a first step, we studied the survival, growth, and reproduction of different life stages of spotted and meadow knapweed over three years. Both knapweeds showed moderate to high seed germination, low survival of dormant seeds and early vegetative stages, and moderate to high survival of older vegetative and flowering plants. Spotted knapweed matured to a flowering state more quickly, but also died sooner, than meadow knapweed. Meadow knapweed has the potential to grow to a large size at some locations. This information will be incorporated into plant models for evaluating the potential effectiveness of different control tactics.

Technical Abstract: Centaurea stoebe subsp. micranthos (Spotted Knapweed) and the hybrid C. x moncktonii (Meadow Knapweed) are perennial forbs introduced from Europe, or in the latter case likely also originating in North America. They are invasive in grasslands and pastures in different regions, including increasingly the Northeast. We collected data from four life stages on 11 different demographic rates involving germination, survival, growth, and fecundity. Four populations of Meadow Knapweed and three populations of Spotted Knapweed were monitored over 3 years in New York State by marking and tracking individual plants. Both Knapweeds showed moderate to high rates of seed germination, very low survival of dormant seeds, and low survival of early vegetative stages with some site-specific exceptions. Survival of older vegetative and flowering plants was generally moderate to high. The main life history differences between Knapweed taxa involved more rapid maturation to and higher mortality of the flowering stage of Spotted Knapweed, a greater tendency for Spotted Knapweed to alternate between a flowering and vegetative state, and the potential for Meadow Knapweed to grow much larger in size. Spotted Knapweed matured more slowly compared to more western populations. Also, flower head-infesting flies (Urophora quadrifasciata) and weevils (Larinus spp.) were present at all study sites. These data add to the knowledge of Knapweed demography and can offer insights into the continued expansion and control of these invasive plants.