Mowing strategies for controlling Cirsium arvense in a permanent pasture in New Zealand compared using a matrix model

• Published in: Ecology and evolution 2016-05, Vol.6 (9), p.2968-2977
• Main Authors: Bourdôt, Graeme W., Basse, Britta, Cripps, Michael G.
• Format: Article
• Language: English
• Subjects: Arvenses; Autumn; Californian thistle; Canada thistle; Cirsium arvense; creeping thistle; Defoliation; Experiments; Grasslands; management; mathematical model; Mowing; Optimization; Original Research; Overwintering; Pasture; perennial thistle; Photosynthesis; Population decline; Population density; Population dynamics; Population growth; Sheep; Spring (season); Summer; Weeds
• ISSN: 2045-7758; 2045-7758
• DOI: 10.1002/ece3.2090

Defoliation has frequently been proposed as a means of controlling Cirsium arvense (L.) Scop. (Californian thistle, Canada thistle, creeping thistle, perennial thistle), an economically damaging pastoral weed in temperate regions of the world, but its optimization has remained obscure. We developed a matrix model for the population dynamics of C. arvense in sheep‐grazed pasture in New Zealand that accounts for the effects of aerial shoot defoliation on a population's photosynthetic opportunity and consequential overwintered root biomass, enabling mowing regimes varying in the seasonal timing and frequency of defoliation to be compared. The model showed that the long‐term population dynamics of the weed is influenced by both the timing and frequency of mowing; a single‐yearly mowing, regardless of time of year, resulted in stasis or population growth, while in contrast, 14 of 21 possible twice‐yearly monthly mowing regimes, mainly those with mowing in late spring, summer, and early autumn, resulted in population decline. Population decline was greatest (with population density halving each year) with twice‐yearly mowing either in late spring and late summer, early summer and late summer, or early summer and early autumn. Our results indicate that mowing can be effective in reducing populations of C. arvense in pasture in the long term if conducted twice each year when the initial mowing is conducted in mid spring followed by a subsequent mowing from mid summer to early autumn. These mowing regimes reduce the photosynthetic opportunity of the C. arvense population and hence its ability to form the overwintering creeping roots upon which population growth depends. A matrix model for the population dynamics of the agricultural weed C. arvense (Californian thistle) in sheep‐grazed pasture in New Zealand was used to compare seasonal mowing regimes. Our results indicate that mowing can be effective in reducing populations of C. arvense in pasture in the long term if conducted twice each year in late spring and/or summer, a period in the year when the aerial shoots are flowering and new root mass is being formed. By contrast, mowing early in the spring when the aerial shoots have not yet begun to flower and the new roots that will overwinter the population are not yet forming, or in the autumn when the aerial shoots are senescing prior to the winter and the overwintering root mass has already been created, is not effective in causing population decline.