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GRAPE GRO WING Managing Weeds Without Herbicides Six options for commercial organic grapegrowers By Toby Bekkers chemical weed control is seen as somewhat of a holy grail among organic grapegrow- ers. In the absence of herbicides, expecta- tions of vineyard appearance, management intensity and cost require adjustment. However, a number of potential benefits balance the equation and make these tech- niques a tangible option for organic and conventional growers alike. W Context The vineyard we recognize today—par- ticularly the country club look of a single-species cover crop and ruler-sharp under-vine herbicide strip—is a relatively modern development. Only a generation ago, herbicide was a new innovation. One can understand the rapid shift from labor-intensive, under-vine cultivation to a simpler, more cost-effective alternative at that time. However, this transition may not be without negative consequences, and the world in which we operate and its toler- ance to some practices has changed for a number of reasons. The motivators for adoption of nonchemical weed control are varied and include the following: Organic certification Certified-organic production precludes the use of herbicide in order to service a seg- ment of the market that wishes to consume products manufactured without the use of chemical inputs. Generally, certified-or- ganic growers pursue the goals of healthy soils and farms, which they believe are best achieved in the absence of chemical inputs. Operator safety, waste disposal Issues such as operator safety and waste disposal are much better understood and, consequently, are more heavily regulated than at any time in the past. For many businesses these factors contribute to the decision to move to alternative practices. eed control is almost uni- versally cited as the most difficult management challenge for organic farms, and finding cost- effective alternatives to Soil health in the under-vine strip therefore fruit quality. Given the importance of microbial activity in making nutrients available to plants in organic systems, this theory probably has some merit. By observa- tion, I would suggest that the effects on soil structure are likely to be equally important when it comes to limiting vine potential. M Physical soil attributes under long-term herbicide regimes appear to me to be negatively affected due largely to the absence of the aerating and soil carbon benefits of plant (i.e., weed or pasture) root activity. Herbicide strips often appear compacted and 'capped' with a layer of hard topsoil. The capacity of these soils to accept water and air must, therefore, be reduced, as likely would happen to microbial activity in the absence of plant-produced substrates for growth. The belief that healthy soils optimize plant performance and wine quality has become widespread among leading producers. In visiting 30 top-tier vineyards in Europe during the past two years, some were organic, some Biodynamic, some conventionally managed in every other way, but not one was using herbicide in the vineyard. T.B. Weed resistance and persistence Weed problems in vineyards can gener- ally be narrowed down to a small number of the most persistent weed species that remain after consistent chemical weed control. The easily killed species become hard to find, the under-vine population becomes less diverse and consists of a handful of the hardest-to-kill species. In addition, there is the possibility of herbicide resistance, with the increasing incidence of annual ryegrass resistance to glyphosate a notable example. Alternative techniques leverage the benefits of physi- cal weed removal and enhanced popula- tion diversity whereby persistent/resistant species become a smaller percentage of the weed population. Community and consumer expectations Farming practices are under more scru- tiny than ever from both customers and the wider community. Whether right or wrong, these expectations change the business environment and motivate many to consider a change in practice. Those that choose organic certification have no choice but to eliminate herbicide, but many others are beginning to make a voluntary shift in anticipation of buyer or community expectations becoming even more rigid. Organic weed-control options What, then, are the options available in the absence of herbicide, and what are the benefits and pitfalls of each? From my perspective the following six options offer a suite of techniques that have potential for use in commercial vineyards. Mechanical weeding Mechanical under-vine weeding is the most widespread organic weed-control technique. Traditionally, under-vine WINES & VINES SEPTEMBER 2012 61 any people believe that prolonged herbicide use affects soil biotic activity. The result of this, it is believed, is a reduction in the grapevine's ability to interact naturally with its soil and environment, with effects on plant resilience and