Multiple Stresses and the Case for Ecologically Based Weed Management.

In contemporary cropping systems, weed management remains a euphemism for “which herbicide(s)?” Herbicides are a simple, cost-effective solution to a pervasive problem, and there are few, if any, disincentives related to the external costs of their use. Herbicides and the focus on controlling weed seedlings, however, provide an ephemeral solution, reducing loss of crop yield and quality in the short-term, but without long-term benefits, or improvements in weed management. Cultivation is likewise a simple solution to the weed problem, but comparatively is less effective, more variable in efficacy, highly dependent on weather, and much slower. And, surviving weeds produce abundant seed rain ensuring future weed problems. GPS- and camera-based guidance systems offer greater precision and higher working rates, but the fundamental problems related to crop-weed selectivity and efficacy remain. Fully autonomous robotic weeders could address these issues. For example, low and variable efficacy would not be a concern as a robot could make as many passes as required to achieve a desired outcome. Despite this promising future, long-term progress in weed management requires a broader view of weed ecology, considering seeds and propagules, dispersal, predation, germination ecology, seedling mortality, competition and seed rain. It requires more thoughtful management of cropping system components and exploitation of a greater diversity of stresses targeting opportunities in key weed life-history stages. While weed seedlings remain a focal point, as important are strategies that reduce the seed (propagule) bank in the soil. High level ecological weed managers are generally found in the organic farming community, where diversity, soil quality, reduced reliance on off-farm inputs, and environmental stewardship are foundational principles guiding production. A greater diversity of crops and disturbances provides the multiple stresses required to manage weeds without, or with reduced reliance on herbicides.