Demography of Meadow and Spotted Knapweed Populations in New York

Lindsey R. Milbrath^1,* and Jeromy Biazzo¹

¹USDA-ARS Robert W. Holley Center for Agriculture and Health, 538 Tower Road, Ithaca, NY 14853. *Corresponding author.

Northeastern Naturalist, Volume 27, Issue 3 (2020): 485–501

Abstract
Centaurea stoebe subsp. micranthos (Spotted Knapweed) and the hybrid C. x moncktonii (Meadow Knapweed) are perennial forbs introduced from Europe; the latter also originated from hybridization in North America of 2 other introduced knapweed species. They are invasive in grasslands and pastures in various regions of North America, including increasingly in the Northeast. We collected data from 4 life stages on 11 different demographic rates involving germination, survival, growth, and fecundity. We monitored 4 populations of Meadow Knapweed and 3 populations of Spotted Knapweed 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 in New York than in more western populations. Also, the flower head-infesting fly 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.

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