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

Abstract

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.

Screening barrier plants to reduce crop attack by sweet potato weevil (Cylas formicarius)

“…1,2 The amount of edible energy that can be produced per hectare is matched by few other crops and in some parts of the world, sweet potato is relied on to provide food when other crops fail. 3,4 The high yield potential of sweet potato is often not realized in smallholder farming where poor knowledge of pests and a low availability of management options mean that little is done to manage pest attack. 5,6 The sweet potato weevil, Cylas formicarius (Fabricius) is considered the most problematic pest of sweet potato as even light infestations can render roots unfit for human consumption.…”

“…5,6 The sweet potato weevil, Cylas formicarius (Fabricius) is considered the most problematic pest of sweet potato as even light infestations can render roots unfit for human consumption. 4,7,8 This pest is effectively controlled by a combination of sanitation, insecticides and pheromone trapping in industrial agricultural parts of the world. These methods are less available and appropriate in developing countries, presenting the need for other, 'low-tech' and affordable methods that can be used by smallholder farmers.…”

“…These methods are less available and appropriate in developing countries, presenting the need for other, 'low-tech' and affordable methods that can be used by smallholder farmers. 4,6 Smallholder agriculture is usually limited by space and intercropping is common, providing opportunities for pest management through cultural and habitat management techniques to establish pest-free crops and minimize pest build-up. [9][10][11] Weevil damage is reduced by intercropping sweet potato with onion (Allium cepa L.), 12 rice (Oryza sativa L.), cowpea (Vigna unguiculata (L.) Walp.…”

Pests, diseases and crop protection practices in the smallholder sweetpotato production system of the highlands of Papua New Guinea

“…In developed country production systems, losses are prevented by the availability of infrastructure such as cool storage facilities and rapid transportation systems. In subsistence production systems, however, post-harvest losses are avoided only by progressive harvest on-demand for immediate use (Okonya et al, 2014), with the general lack of infrastructure otherwise leading to high levels of damage (Johnson & Gurr, 2016). This slows the development of commercial production and the livelihood benefits that value chains and processing potentially offer to impoverished rural communities.…”

“…Sweetpotato is attacked by around 300 species of arthropods (Talekar, 1991) that can cause severe to complete crop loss, as well as at least 30 diseases (Clark et al, 2013; Johnson & Gurr, 2016) provide a recent, comprehensive review of those most common in smallholder production. The fact that sweetpotato is vegetatively propagated, either by storage root fragments (slips) or by stem cuttings means that there is high scope for transfer of pest and pathogen inoculum from old to new crops.…”