Management strategies for an invasive weed: A dynamic programming approach for Californian thistle in New Zealand

Abstract

Invasive plants can cause significant problems in natural and agricultural ecosystems. Although research has already been conducted on the economics of a single-control option for some invasive weeds, we extended the analysis by developing a dynamic optimisation model that evaluates the net benefits of a range of possible control options simultaneously in order to identify the optimal strategy (mix of control options). This paper focuses on Californian thistle (Cirsium arvense) in pasture in New Zealand. The net benefit is maximised by considering the costs and efficacy of control options, and the monetary value of animal production. Trajectories of shoot density are developed and the optimal strategies are found. Our results suggest that the introduction of a biological control agent (Apion onopordi), in combination with one or more control options, is the optimal strategy when the initial density of the thistle population exceeds 1.0 shoot m -2 . Results show that in the setting of the model excluding MCPA, MCPB and a Sclerotinia sclerotiorum-based mycoherbicide reduces the net present value (NPV) by less than 2%.

Minimizing environmental impacts of grassland weed management: can Cirsium arvense be controlled without herbicides?

“…, 2008). This apparent contradiction with our study arises because Chalak‐Haghighi et al. (2008) assumed that grazing would damage the thistle directly, but did not consider grazing effects on competing species.…”

“…, 2004). A modelling study of C. arvense control in New Zealand suggested high infestations could best be controlled by a combination of herbicides and intensive grazing (Chalak‐Haghighi et al. , 2008).…”

Optimal Integrated Strategies to Control an Invasive Weed

“…The expected efficacy multiplier, E(), for those strategies that include only a single treatment option (strategies 2–8 and 25) are obtained from the literature, as presented in Table . The expected efficacy multipliers of the strategies that are a combination of more than one control option are calculated from the following formula (from Chalak‐Haghighi et al ) where is the expected efficacy multiplier of control strategy, s = {1, …, S } are control options included in the strategy, and is the efficacy multiplier of control option s (i.e., the proportion of weeds removed).…”

“…These studies have generally examined only a small number of discrete control strategies, often only one. IWM approaches that emphasize the use of several control measures (Buckley et al ; Pannell et al ; Chalak‐Haghighi et al ) are often suggested to be the preferred way of controlling invasive weeds, relative to chemical‐only strategies (e.g., Pardo et al ). This study tests this hypothesis, which has rarely been done for environmental weeds.…”

“…Although there have been a number of studies evaluating management strategies for weeds and other pests (e.g., Vere et al 2004;Eiswerth and van Kooten 2007;Llewellyn et al 2007;Fried et al 2012), there has not been an economic analysis of control strategies to deal with blackberry in the natural environment. Dynamically optimal weed control decision rules have been derived in a number of studies, including Wu (2001), Taylor and Burt (1984), Kennedy (1987), McConnachie et al (2003), Chalak-Haghighi et al (2008), and Chalak et al (2009). These studies have focused on weed control for agricultural benefits.…”