Spatiotemporal dynamics and modelling support the case for area-wide management of citrus greasy spot in a Brazilian smallholder farming region

Laranjeira, F. F.; Silva, S.X.B.; Murray-Watson, Rachel E; Soares, Ana Cristina Fermino; Santos-Filho, H.P; Cunniffe, Nik J.

doi:10.1101/839431

“…For example, we do not consider spatial effects (Shaw, 2000;Parnell et al, 2005Parnell et al, , 2006, which could explore how resistance might develop on a regional scale. Management decisions made by one grower affect the entire community due to dispersal of aerial inoculum (Laranjeira et al, 2020). Future work might address how decisions made by growers can adversely affect others, and what policy changes can be used to incentivise sustainable behaviour.…”

mentioning

confidence: 99%

Optimal Resistance Management for Mixtures of High-Risk Fungicides: Robustness to the Initial Frequency of Resistance and Pathogen Sexual Reproduction

Taylor

¹

,

Cunniffe

²

2023

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There is a strong consensus that selection for fungicide resistant pathogen strains can be most effectively limited by using applications of mixtures of fungicides designed to balance disease control against selection. However, how to do this in practice is not entirely characterised. Previous work indicates optimal mixtures of pairs of fungicides which are both at a high risk of resistance can be constructed using pairs of doses which select equally for both single resistant strains in the first year of application. What has not been addressed thus far is the important real-world case in which the initial levels of resistance to each fungicide differ, for example because the chemicals have been available for different lengths of time. We show how recommendations based on equal selection in the first year can be sub-optimal in this case. We introduce a simple alternative approach, based on equalising the frequencies of single resistant strains in the year that achieving acceptable levels of control is predicted to become impossible. We show that this strategy is robust to changes in parameters controlling pathogen epidemiology and fungicide efficacy. We develop our recommendation using a pre-existing, parameterised model of Zymoseptoria tritici (the pathogen causing Septoria leaf blotch on wheat), which exemplifies the range of plant pathogens which predominantly spread clonally, but for which sexual reproduction forms an important component of the life cycle. We show that pathogen sexual reproduction can influence the rate at which fungicide resistance develops, but does not qualitatively affect our optimal resistance management recommendation.

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“…This requires partitioning limited resources for disease management between the population of particular interest and the growing epidemic elsewhere, and determining whether this partitioning should vary with time and with the current state of the epidemic [64]. This must be done in a situation in which different sets of stakeholders have different objectives [65], but must nevertheless work together [66]. We used the outbreak of sudden oak death in Humboldt County, California, to motivate our work.…”

Section: Discussionmentioning

confidence: 99%

Optimal strategies to protect a sub-population at risk due to an established epidemic

Bussell

¹

,

Cunniffe

²

2022

J. R. Soc. Interface.

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Epidemics can particularly threaten certain sub-populations. For example, for severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), the elderly are often preferentially protected. For diseases of plants and animals, certain sub-populations can drive mitigation because they are intrinsically more valuable for ecological, economic, socio-cultural or political reasons. Here, we use optimal control theory to identify strategies to optimally protect a ‘high-value’ sub-population when there is a limited budget and epidemiological uncertainty. We use protection of the Redwood National Park in California in the face of the large ongoing state-wide epidemic of sudden oak death (caused by Phytophthora ramorum ) as a case study. We concentrate on whether control should be focused entirely within the National Park itself, or whether treatment of the growing epidemic in the surrounding ‘buffer region’ can instead be more profitable. We find that, depending on rates of infection and the size of the ongoing epidemic, focusing control on the high-value region is often optimal. However, priority should sometimes switch from the buffer region to the high-value region only as the local outbreak grows. We characterize how the timing of any switch depends on epidemiological and logistic parameters, and test robustness to systematic misspecification of these factors due to imperfect prior knowledge.

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“…There are various possible criticisms of the model used to generate these results, such as the lack of consideration of spatial effects (Shaw, 2000;Parnell et al, 2005Parnell et al, , 2006, which could explore how resistance might develop on a regional scale. Management decisions made by one grower affect the entire community due to dispersal of aerial inoculum (Laranjeira et al, 2020). A spatially explicit model would also allow reactive disease management to be optimised (Cunniffe et al, 2015b(Cunniffe et al, , 2016, which would correspond to levels of fungicide treatment depending on local disease intensity, or even the results of a decision support type system (Carisse, 2010;Jorgensen et al, 2017;Lázaro et al, 2021).…”

Section: Discussionmentioning

confidence: 99%

Optimal resistance management for mixtures of high-risk fungicides: robustness to the initial frequency of resistance and pathogen sexual reproduction

Taylor

¹

,

Cunniffe

²

2022

Preprint

2

0

View full text Add to dashboard Cite

There is a strong consensus that selection for fungicide resistant pathogen strains can be most effectively limited by using applications of mixtures of fungicides designed to balance disease control against selection. However, how to do this in practice is not entirely characterised. Previous work indicates optimal mixtures of pairs of fungicides which are both at a high risk of resistance can be constructed using pairs of doses which select equally for both single resistant strains in the first year of application. What has not been addressed thus far is the important real-world case in which the initial levels of resistance to each fungicide differ, for example because the chemicals have been available for different lengths of time. We show how recommendations based on equal selection in the first year can be sub-optimal in this case. We introduce a simple alternative approach, based on equalising the frequencies of single resistant strains in the year that achieving acceptable levels of control is predicted to become impossible. We show that this strategy is robust to changes in parameters controlling pathogen epidemiology and fungicide efficacy. We develop our recommendation using a pre-existing, parameterised model of Zymoseptoria tritici (the pathogen causing Septoria leaf blotch on wheat), which exemplifies the range of plant pathogens which predominantly spread clonally, but for which sexual reproduction forms an important component of the life cycle. We show that pathogen sexual reproduction can influence the rate at which fungicide resistance develops, but does not qualitatively affect our optimal resistance management recommendation.

show abstract

Spatiotemporal dynamics and modelling support the case for area-wide management of citrus greasy spot in a Brazilian smallholder farming region

Cited by 4 publications

References 32 publications

Optimal Resistance Management for Mixtures of High-Risk Fungicides: Robustness to the Initial Frequency of Resistance and Pathogen Sexual Reproduction

Optimal Resistance Management for Mixtures of High-Risk Fungicides: Robustness to the Initial Frequency of Resistance and Pathogen Sexual Reproduction

Optimal strategies to protect a sub-population at risk due to an established epidemic

Optimal resistance management for mixtures of high-risk fungicides: robustness to the initial frequency of resistance and pathogen sexual reproduction

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