The frequency and extent of crop losses caused by plant diseases and pests is another gap in our knowledge and understanding of agrifood systems (see P. Sukhdev et al. Nature 540, 33–34; 2016). This information is crucial for developing sustainable strategies to manage crop health. Such losses can never be eliminated completely, and occur in many ecosystems. Declining crop health affects farmers, consumers and societies through higher input costs, lower outputs and damage to environmental and human health through the abuse and misuse of pesticides. To try to quantify the problem, the International Society for Plant Pathology's online global survey of experts in crop health (https://globalcrophealth.org) is determining the importance of crop pests and diseases in five staple crops: wheat, rice, maize (corn), soya bean and potato. So far, around 75% of responses report losses every season, with one-third experiencing yield reductions of 5–60% each year. The survey, which ends on 31 January, has revealed large geographical gaps in the available expert knowledge on crop losses. Such gaps must be addressed to improve access to crop-health information and to increase understanding of today's needs and priorities for future sustainable food systems.