Rats in rice: linking crop and pest models to explore management strategies Peter R. Brown A,E , Nguyen Thi My Phung A,B,C and Donald S. Gaydon D A CSIRO Ecosystem Sciences and CSIRO Sustainable Agriculture Flagship, GPO Box 1700, Canberra, ACT 2601, Australia. B An Giang Plant Protection Department, Long Xuyen, An Giang, Vietnam. C School of Animal Studies, University of Queensland, Gatton Campus, Qld, Australia. D CSIRO Ecosystem Sciences, Dutton Park, Brisbane, Qld 4102, Australia. E Corresponding author. Email: peter.brown@csiro.au Abstract Context. Rodents cause yield losses of 10–15% in irrigated lowland rice crops in Vietnam, with farmers spending a lot of time and money trying to control them. Despite this, there is little understanding about the optimal timing of rodent control and the level of reduction required to maximise rice crop yields. This is compounded by the ability of rice crops to compensate for damage, and farmers applying control at the wrong time. Aims. We explored the optimal timing and intensity of rodent control required to increase yields of irrigated lowland rice crops in the Mekong Delta, Vietnam. Methods. We developed a system analysis framework using the rice model APSIM-Oryza validated against a hand- clipped field experiment, linked with a rodent population model and field data on rodent damage rates in rice crops. A range of intensities of reduced feeding rates and timing were explored in simulated scenarios. The responses were examined over three rice crop seasons in An Giang province, Mekong Delta, Vietnam. Key results. The rice crop model was benchmarked, validated and shown to adequately compensate for rodent damage. Highest yield losses occurred in the third rice crop (16% yield loss). A one-off rodent control action at the booting stage of the rice crop with 50% control effectiveness achieved a 5% yield increase. The community trap barrier system (CTBS) with 30% control effectiveness achieved a 5% yield increase. Conclusions. The modelling demonstrated the importance of rodent management timing and that control should be applied before the onset of the rodent breeding season, which normally starts at maximum tillering or booting stages. Implications. We conclude that modelling can improve pest management decisions by optimising timing and level of effectiveness to achieve yield increases. Additional keywords: APSIM-Oryza, compensation, damage, irrigated lowland rice, ricefield rats, Vietnam. Received 22 October 2010, accepted 5 May 2011, published online 30 November 2011 Introduction Rodents cause significant damage to a wide range of agricultural crops throughout the world (Singleton et al. 1999, 2010a; Stenseth et al. 2003). There is a strong desire to effectively reduce the damage that rodents cause to agricultural crops to improve farmers’ yields and income, but also to improve food security (Meerburg et al. 2009; Singleton et al. 2010b). This is particularly relevant in Vietnam, where the production of rice is one of the most important industries and engages a large proportion of the population (Huan et al. 2010). In Vietnam, farmers can grow 2–3 rice crops per year in the irrigated lowland rice cropping system, which is critically important for food security and export (Huan et al. 2010). Rodents have been described as one of the top three pests of rice in Vietnam (Huynh 1987) and the most important pest species to control (Tuan et al. 2003). Yield losses are normally 10–15%, but can reach up to 100% in some circumstances (Brown et al. 2006; Brown and My Phung 2010; Huan et al. 2010). For this reason, the management and control of pests such as rodents is important to Vietnam’s long-term agricultural productivity. In agricultural cropping systems in Vietnam, and indeed in cropping systems throughout the world, the management of rodent pests is largely guided by field experience, which is often scant or based on a small number of field experiments that may not be applicable to other situations or at different times. Furthermore, there is little understanding about the optimum timing of control and the potential benefits flowing from these control measures (Yokomizo et al. 2009). It is often not known whether rodent control actually leads to a reduction in levels of damage or increased crop yields (sensu Hone 2007), and CSIRO PUBLISHING Wildlife Research, 2011, 38, 560–567 http://dx.doi.org/10.1071/WR10194 Journal compilation Ó CSIRO 2011 www.publish.csiro.au/journals/wr