Emerging pests and diseases of South‐east Asian cassava: a comprehensive evaluation of geographic priorities, management options and research needs

Abstract

Cassava is a major staple, bio-energy and industrial crop in many parts of the developing world. In Southeast Asia, cassava is grown on >4 million ha by nearly 8 million (small-scale) farming households, under (climatic, biophysical) conditions that often prove unsuitable for many other crops. While SE Asian cassava has been virtually free of phytosanitary constraints for most of its history, a complex of invasive arthropod pests and plant diseases has recently come to affect local crops. We describe results from a region-wide monitoring effort in the 2014 dry season, covering 429 fields across five countries. We present geographic distribution and field-level incidence of the most prominent pest and disease invaders, introduce readily-available management options and research needs. Monitoring work reveals that several exotic mealybug and (red) mite species have effectively colonised SE Asia's main cassava-growing areas, occurring in respectively 70% and 54% of fields, at average field-level incidence of 27 ± 2% and 16 ± 2%. Cassava witches broom (CWB), a systemic phytoplasma disease, was reported from 64% of plots, at incidence levels of 32 ± 2%. Although all main pests and diseases are non-natives, we hypothesise that accelerating intensification of cropping systems, increased climate change and variability, and deficient crop husbandry are aggravating both organism activity and crop susceptibility. Future efforts need to consolidate local capacity to tackle current (and future) pest invaders, boost detection capacity, devise locally-appropriate integrated pest management (IPM) tactics, and transfer key concepts and technologies to SE Asia's cassava growers. Urgent action is needed to mobilise regional as well as international scientific support, to effectively tackle this phytosanitary emergency and thus safeguard the sustainability and profitability of one of Asia's key agricultural commodities. © 2016 Society of Chemical Industry.

Peer Review #1 of "Continental-scale suppression of an invasive pest by a host-specific parasitoid underlines both environmental and economic benefits of arthropod biological control (v0.2)"

“…Manuscript to be reviewed wide release (Neuenschwander, 2001). Following its devastating passage through Africa's cassava belt in the 1970s and 80s, P. manihoti was inadvertently introduced into Thailand in 2008, spread through mainland Southeast Asia, and made its appearance in Indonesia by 2010 (Graziosi et al, 2016). As cassava is grown on >4 million ha by an estimated 8 million farming families throughout tropical Asia, this pest had potential to cause massive socio-economic impacts.…”

Modeling Epidemics in Seed Systems to Guide Management Strategies: The Case of Sweetpotato in Northern Uganda

“…The problem of seed-transmitted viral introduction was illustrated in 2014 when Sri Lankan cassava mosaic virus (causing cassava mosaic disease) was first detected in Southeast Asia, presumably being introduced through infected seed material. Efforts are still ongoing to mitigate spread and deploy resistance before this yield-robbing disease takes hold (Graziosi et al 2016; Wang et al 2016). Another dramatic example occurred in 2011 when maize lethal necrosis (MLN) was first reported in Kenya (Wangai et al 2012) and soon was detected in several other Sub-Saharan African countries.…”

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“…As phytosanitary pressures on cassava increase (Graziosi et al, 2016), formal 'clean seed' initiatives 764…”

“…Vietnam and Cambodia's cassava boom has coincided with the emergence and spread of a host of 63 pests and diseases, including the cassava mealybug and cassava witches broom disease (CWB) 64 (Alvarez et al, 2013;Graziosi et al, 2016). The most recent arrival is a member of the cassava 65 mosaic virus family of geminiviruses, the Sri Lanka Cassava Mosaic Virus (SLCMV) (Wang et al, 66 2016).…”

“…Endemic to India and Sri Lanka, SLCMV is disseminated both by Bemisia tabaci whitefly, 67 and through the movement of infected planting materials (Legg, 2010). The appearance of SLCMV is 68 part of a larger pattern of pest and disease invasion in Southeast Asian cassava (Graziosi et al, 2016), 69 including interacting co-infections by several pest species (Wyckhuys et al, 2017). These threats to 70 the multi-billion dollar regional industry, all transmissible by the movement of contaminated planting 71 material, call for an increased understanding of existing cassava seed systems.…”