Invertebrate pests and diseases of sweetpotato (Ipomoea batatas): A review and identification of research priorities for smallholder production

Sweetpotato has been the subject of little research worldwide compared with other major crop staples, and this is especially so for less developed countries where sweetpotato is critical for food security. This review synthesises information on plant protection issues that affect smallholder sweetpotato farmers in less developed countries to identify major issues and suggest research priorities. Though the pests and diseases of sweetpotato in less developed countries are largely common to industrialised systems, their relative importance differs and losses tend to be more severe as a result of differing agronomic practices and relative unavailability of management options and technical support that are important in developed countries. Smallholders are heavily reliant on cultural practices such as traditional forms of biological control using ants and livestock, fallowing and composting (sometimes with plant materials having biocidal properties). Crop protection methods that have been developed for use in sweetpotato production in developed countries, such as pathogen-tested planting material, early maturing varieties, pheromone trapping and pesticides are less accessible to, and relevant for, smallholders. Smallholders also typically harvest a given crop progressively which extends the period over which storage roots are potentially vulnerable to attack but reduces the risk of post-harvest losses. Human population growth in developing countries is leading to an increase in cropping intensity with shorter fallow periods and more years of continuous crops. This has the dual effect of depleting soil nutrients and increasing the potential for pest and pathogen build-up. Associated with this, the adoption of strategies to manage crop nutrition, such as not burning crop residues, promote carryover of pests and pathogen inocula. As a consequence of these factors, sweetpotato yield losses from diseases, especially viruses, and pests, particularly weevils, can be high. Climate change is likely to result in more frequent drought and this will increase losses caused by sweetpotato weevils that are favoured by dry conditions. This review of sweetpotato pests and their management options concludes with suggestions for some future research priorities including the combination of traditional practices that have pest management outcomes with relevant practices from industrial production that are able to be transferred or modified for use in smallholder production. Increased technical support for decision making and diagnostics, including molecular approaches that have scope for field use, will be important in reducing the burden imposed by biotic threats to this important global crop.