Plant pathogens – the great thieves of vegetable value

Plant diseases are responsible for considerable losses in many crops. Most plant diseases cause a reduction in yield of the infected plants with diminished quantity and/or quality of harvested plant products, but the extent of damage and loss can vary greatly. To most vegetable growers, in crop or post-harvest disease invariably rates as the greatest impact on their profitability. Disease “steals” both quantity and quality from production, and necessitates additional cost and time inputs in disease mitigation. Estimation of these losses can be difficult, and in this paper I argue the full costs of disease are often underestimated. Measuring direct yield losses associated with plant disease is generally difficult to determine as disease symptoms may be obscure or difficult to distinguish from other diseases or abiotic factors; disease may be have a variable impact on plants depending upon its stage of development and crop maturity; disease may be aggregated within field requiring careful and intensive sampling strategies; there may be a lack of suitable populations of healthy and diseased populations to provide adequate comparisons; and there may be compensatory effects from healthy plants following removal of plants by disease. Loss estimates are invariably highly varied. The costs of disease are of course not restricted to the economic impact of reduced yields or diminished quality. Financial losses from increased production costs, additional costs associated with disease mitigation, and lost markets can be substantial. Furthermore, significant social and environmental costs can also result from plant disease. In this paper I examine holistically the range of “costs” associated with plant disease. Using select potato diseases as case studies I highlight some of the obvious and hidden costs of disease and suggest a more thorough examination of the impact of individual diseases is required in prioritising investment in disease management.