Developing and disseminating potato virus management strategies for northeastern growers
There are economic and environmental imperatives for the development of biological disease control strategies for Potato Virus Y (PVY). PVY is an economically important crop disease that reduces yield and, in the worst cases, causes crop failure in many solanaceous crops, including potatoes, tomatoes, tobacco, peppers, and eggplants. PVY presents a daunting management challenge, because it is transmitted rapidly by a vast array of aphid species and infected plants can be difficult to identify in the field. Current strategies, such as pesticide applications and removal of infected plants from the field, are not effective, needlessly increasing chemical inputs at both an economic and environmental cost.
The goal of this project was to develop and disseminate a biological disease control strategy for potato growers that minimizes PVY spread by enhancing naturally occurring aphid natural enemy populations. To begin this work, a total of twenty-two farms were surveyed for aphids, aphid natural enemies, and PVY over two growing seasons (2012 and 2013), and the landscape composition of the area surrounding the farm was analyzed using ArcGIS software. In both 2012 and 2013, there was a significant positive relationship between the amount of agricultural land surrounding a farm and the end of season PVY prevalence on farms with infection; the more agriculture in the area, the more PVY there was, given an introduction of the virus in the potato seed tubers. The insect community across the region is extremely diverse, including at least 54 species of aphids, and the aphid natural enemy assemblage includes seven species of ladybugs, as well as lacewings, and pirate bugs. This diversity had an inconsistent effect on the final PVY prevalence; in 2012, there was a significant positive relationship between aphid abundance and PVY prevalence, but a significant negative relationship in 2013. In 2013, PVY prevalence was also negatively associated with aphid species richness. In 2012, PVY prevalence was negatively associated with lady bug species richness; there was no effect in 2013.
1) Survey the main aphid vector species, common natural enemies of aphids, and the distribution and spread of PVY on small farms across several counties in New York State: I conducted this survey for two field seasons (2012 and 2013) and have completed this aspect of the project. The results of this work have been presented to growers in fact sheets, and will be published as two scientific papers.
2) Evaluate the influence of landscape-level effects: Using GIS software, I analyzed the landscape composition of the area surrounding the potato fields at three scales: within radiuses of 0.5km, 1km, 1.5km. Land use was quantified as %agricultrual, %forested, %developed, etc. There was a significant positive relationship between final virus prevalence and amount of agricultural land within 500m and 1000m in 2012, and at all three scales in 2013; the most predictive scale was 1000m in 2012 and 500m in 2013. The amount of natural habitat (forested land and grassland) within the same scales had the opposite effect on final PVY prevalence; percent natural habitat a significant negative effect on PVY prevalence at 500m and 1000m in 2012 and all three scales in 2013. The most predictive scale was 1000m in both 2012 and 2013.
While the percent agriculture had no effect on the ladybug community in either year, it had a significant negative effect on aphid species richness in both years. Further analysis of the relationship between landscape composition, within-season variation (measured as sampling week), and the aphid community is still underway, but the preliminary results indicate that landscape composition (measured as percent cropland) and seasonal variation interactively affect aphid abundance, species richness, and functional community composition (the percentage of aphids collected that were PVY vectors).
3) Evaluate the influence of aphid community composition on PVY prevalence and spread: In field and greenhouse experiments conducted in the summer and fall of 2014, I examined the impact of aphid density and species diversity and on aphid movement and PVY prevalence. Analysis on these projects is ongoing, but preliminary results indicate that the movement of a colonizing aphid species (one that settles and reproduces on potatoes) is more affected by the abundance of their conspecifics than the abundance of other species, and that different non-colonizing species affect their movement differently. This project also demonstrates that aphid community composition has a significant effect on PVY transmission. This effect is species-specific, and does not depend on species richness.
4) Evaluate the effect of natural enemy community composition on PVY prevalence and spread: Field populations of aphid natural enemies did not have an effect on the aphid community in the landscape level project. In fact, it appears that the aphid community drives natural enemy abundance and species richness, not vice versa.
5) Disseminating disease control management strategies: Cumulatively, the data from the landscape project suggests that more natural habitat and less agricultural land surrounding an infected farm will help minimize end-of-season PVY prevalence. This data emphasizes the importance of prevention; purchasing disease-free seed tubers and not saving seed remain the best means of avoiding a PVY outbreak. This information, as well as data for each individual farm, was presented in fact sheets that were distributed to each participating grower.
Over the past year, we carried out a field experiment designed to: 1) explore vegetation management strategies for PVY control; and 2) to further unravel the role of particular aphid species in PVY spread. Our experimental design included three treatments (monoculture potato, potato/oat polyculture, and potatoes with an oat border) factorially crossed with three levels of initial inoculum (0%, 5%, and 10% infected plants). We sampled plants for virus infection three times over the season and tracked aphid abundance and species richness using pan traps. Although data analysis is currently in progress, preliminary analysis suggests that oat borders decreased the prevalence of PVY in comparison to potato monocultures, particularly at higher levels of initial infection. Aphid samples are still being sorted and identified, so no results on vectors are available at this time.
In addition, I have completed the analysis of the field and greenhouse experiments conducted in 2014, and further analyzed the landscape-level project data, exploring the spatio-temporal dynamics of the aphid community across the Finger Lakes region. Manuscripts based on these datasets are in preparation and will be submitted in early 2016.
My project has proceeded largely as expected and I have learned a great deal over the course of the last three years. I have gained project management and mentorship experience and learned several new research techniques, which will be essential as I progress in my career.
Impacts and Contributions/Outcomes
The data I have collected has provided useful information about the most common PVY aphid vectors and aphid natural enemy species, as well as the prevalence of PVY on small-scale farms across the Finger Lakes region of NY State. It has also demonstrated the impact of landscape composition on disease spread. This will allow for more effective estimation of the risk of in-season disease spread.
Over the last year, I submitted a manuscript on this project for publication (currently in revision), continued my work on a blog about the intersection of disease and society, directed at a general audience (Direct Transmission, www.directtransmission.org), and disseminated my project results through various outlets. In addition, two more manuscripts are in preparation.
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