Weed management in organic farming

Abstract

Cultivation remains the foundation of weed management in organic farming. Low and variable efficacy, increasingly unpredictable weather, cost, and perceived harm to soil quality inspire organic farmers, to varying degrees, to learn and implement ecologically based management practices. Crop rotation and cover cropping are system-level practices frequently cited as weed management tools; however, unless their implementation is guided by knowledge of weed biology and targeting sensitive life history stages, these practices may have minimal benefit, or even increase weed populations. To reduce cultivation events or improve the outcome of existing events, reduction in the weed seedbank is required, a management goal increasingly adopted by organic farmers. In diversified systems, short-season cash or cover crops can be grown in sequence to completely preempt weed seed rain. Because many weed seeds have relatively short half-lives in the soil, a single season without replenishment by seed rain will have a large effect on their seedbank. In addition to preventing such "credits" to the weed seedbank, organic growers often employ management practices to "debit" the seedbank. Knowledge of weed emergence periodicity and the importance of germination as a mechanism to deplete the seedbank, for example, have contributed to refinements in the use of fallow periods, sometimes varying between early and late season, to avoid proliferation of particular weed species. Innovations in cultivation tools promise improved efficacy, greater working rates, and better control of intrarow weeds. Supporting these tools with ecologically based management practices guided by weed biology knowledge and focused on reducing the seedbank, enhancing crop-weed interference, and managing dispersal will provide durable weed management recommendations for organic farming.