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

Graeme W Bourdôt,Britta Basse,Michael G Cripps

doi:10.1002/ece3.2090

Abstract

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.

Highlights

Mowing pastures infested by Cirsium arvense (L.) Scop. (Californian thistle, Canada thistle, creeping thistle, perennial thistle) (Fig. 1) has long been considered a potentially effective control method for this persistent and economically damaging perennial weed in both its native European and exotic ranges (Canada, USA, Australia, New Zealand)
From the population model that we have developed for C. arvense in permanent grassland, where the size of an ephemeral overwintering root bud population is a linear function of the photosynthetic opportunity attributable to the aerial shoots during the preceding growing season, two conclusions may be drawn concerning the influence of mowing
An annually repeated single mowing, regardless of the time when this is imposed on the shoots during each growing season, is unlikely to cause longterm population decline

Summary

Introduction

Mowing pastures infested by Cirsium arvense (L.) Scop. (Californian thistle, Canada thistle, creeping thistle, perennial thistle) (Fig. 1) has long been considered a potentially effective control method for this persistent and economically damaging perennial weed in both its native European and exotic ranges (Canada, USA, Australia, New Zealand). During the 168 years since this early synthesis, many field experiments have provided substantial evidence that mowing can be effective in reducing C. arvense shoot populations in pastures. They show that the frequency and timing of the defoliation within a growing season, and the number of consecutive years in which it is repeated, all influence the rate of population decline, but their optimal combination remains obscure. A single mowing to ground level in early- to mid-summer, when many of the shoots would have been flowering, caused population decline in C. arvense in pastures a 2016 The Authors.

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Conclusion