POWDERY MILDEW RISK AND FORECASTING IN WINE GRAPES: DO GROWERS CHANGE RISK MANAGEMENT STRATEGIES IN RESPONSE TO DISEASE FORECASTS?

How and how well growers manage the risks inherent in agriculture has direct welfareimplications for producers and consumers at both local and societal levels. While better weather,pest and disease forecast information are rapidly disseminating among producers and are oftentouted as promising inputs to production and risk management, little is known about how thisnew information actually shapes producer behavior in practice. We argue that better forecastinformation can benefit growers and improve their capacity to manage disease and pestseffectively, but that we must jointly consider the various margins of adjustment available togrowers in order to properly understand their response to this improved information. Using thecase of California wine grape growers and high resolution panel data that includes plot-levelpowdery mildew treatments, we characterize growers’ response to a popular powdery mildewrisk model that generates forecast in the form of a daily risk index (PMI). Our analysis suggeststhat growers using the PMI primarily adjust their choice of product in response to the PMI byswitching to higher potency synthetic fungicides when the risk is high. Since these products havelonger minimum intervals, this implies that – if anything – PMI users have longer intervals as thePMI increases. Our preliminary results also suggest that the net environmental impact of thisdocumented multi-dimensional response to the PMI may actually be negative, although weemphasize that these are preliminary results. Futhermore, it is important to note that themagnitude of this effect is small compared to the general improvements in wine grape growers’environmental impact over the past several years.