Economic Thresholds and the Case for Longer Term Approaches to Population Management of Weeds¹

Abstract

The economic threshold is a concept strongly embedded within the weed management literature. There are some theoretical concerns with applying a static approach such as the economic threshold to weed management decision making. An improvement is to adopt a population management approach where the intertemporal effects of decisions are taken into account. The focus should be on managing weed populations through time rather than minimizing the yield effect of weeds in a single season or year. Rather than viewing weeds as an annual production problem, the weed seed bank can be considered a renewable resource stock, and the management goal is to deplete this resource stock through time. The principles of natural resource economics illustrate that including the intertemporal effects of weed control will, for a given size of a seed bank, result in a greater level of weed control and a higher economic benefit than if control decisions were based solely on the current period effects. A dynamic economic model was developed of an extensive Australian spring wheat (Triticum aestivum) cropping system to test these principles using wild oat (Avena fatua and A. ludoviciana) as an example. The model was solved for a 20-yr time horizon for a population management approach and the traditional static economic threshold. The economic benefits from a population management approach were significantly greater than those generated by the economic threshold, and the final seed bank was considerably lower. This result suggests that a paradigm shift from thresholds to longer term population management is warranted.

Nível de dano econômico como critério para tomada de decisão no controle de guanxuma em soja

“…Não controlar uma população de plantas daninhas que se situe próximo do nível de dano pode definir ou não se será excedido um nível de dano em anos subseqüentes (Bauer & Mortensen, 1992;Jones & Medd, 2000). Por isso, o impacto de populações de ervas, mesmo abaixo do nível de dano, sobre o banco de sementes no solo tem sido objeto de muita preocupação.…”

Weed species richness, density and relative abundance on farms in the subtropical grain region of Australia

“…Many species have staggered recruitment patterns and this in conjunction with short life cycles increases the chances of weeds surviving to maturity and producing seeds. Limiting seed production of weed escapes is now recognised as a key goal of weed management programs (Jones and Medd 2000;Medd 1997), and adds emphasis to the planning of weed management programs and the timing of operations.…”

A Cost-Benefit Framework for the Assessment of Non-Tariff Measures in Agro-Food Trade

“…Eisworth and van Kooten, 2002;Taylor and Burt, 1984;Jones and Medd, 2000; see also references in Pimentel et al, 2005). For example, Eiswerth and van Kooten (2002) analyze the supply impact of weed infestation on yield loss and cost of production on hay pastures for a non-indigenous weed, the yellow starthistle, and considering five management alternatives.…”