Introduction

Darin Gibson, Gaia Consulting

Biology and Areawide Management of Beet Leafhopper

Rodney Cooper, USDA ARS

                Beet leafhopper is a vector of “Candidatus Phytoplasma trifolii” (also known as beet leafhopper transmitted viresence agent, BLTVA), the pathogen that causes potato purple top disease and disorders in other vegetable crops.  This insect also transmits beet curly top virus (BCTV), which causes disease symptoms in carrot, coriander, beet, and other vegetable and seed crops.  Beet leafhoppers migrate from weedy mustards in the spring to kochia and Russian thistle during summer.  It is during these migrations between spring and summer hosts that beet leafhopper transmits Phytoplasma to potato.  The timing of beet leafhopper movement generally occurs as mustards and other spring hosts dry down, allowing growers to potentially predict when leafhoppers are likely to arrive in potato.  Understanding these landscape-level factors that regulate beet leafhopper populations and dispersals can be used to predict the risk of purple top disease and to time management strategies when leafhoppers are most likely present.  For example, we maintain a network of traps in ~50 potato fields in the Columbia Basin of Washington to track beet leafhoppers.  A subsample of captured beet leafhoppers are tested for BLTVA and BCTV using high-throughput diagnostic PCR.  Weekly results are shown on the Potato Decision Aid System (potatoes.decisionaid.systems) using contour and pathogen prevalence maps to show leafhopper density, distribution, as well as BLTVA and BCTV infection rates.  We are also identifying the community of natural enemies that potentially help manage leafhopper populations in non-crop habitats before they arrive in potato.  Research showed that several parasitoids, a diversity of spiders, and whirligig mites, are important predators of beet leafhopper in these non-crop habitats.              

Kylie Swisher-Grim, USDA-ARS
Christopher Gorman, Washington State University
Jillian Foutz, USDA-ARS
Bonnie Ohler, Washington State University
Tim Waters, Washington State University
Carrie Wohleb, Washington State University
Davide Crowder, Washington State University

              
First principles of Potato virus Y disease management are critical elements for sustainable control

Russell L. Groves, Univ. of Wisconsin-Madison

               Potato virus Y (PVY) is an aphid-transmitted virus that causes disease in numerous solanaceous crops including tomato, pepper, tobacco, and potato. In potato, PVY can be a yield and quality-limiting pathogen that can cause as much as 50 to 80 percent yield loss in heavily infected commercial lots. Select strains of the virus may also cause post-harvest losses due to tuber necrosis and reduced storage quality. PVY has been successfully managed for decades, but in recent years the virus has re-emerged as a potentially serious disease problem. The emergence of new genetic recombinant strains of PVY that cause mild foliar disease symptoms, the emergence and establishment of new aphid vectors, together with the widespread adoption of potato varieties that express mild symptoms of PVY infection are all thought to contribute to the re-emergence of PVY. For many years seed potato certification programs have succeeded in maintaining PVY levels at low and acceptable levels. However, as described above, the occurrence of new PVY strains, the widespread planting of symptomless varieties, and the increased abundance of late-season colonizing aphid vectors require an adherence to sustainable management strategies that rely upon first principles of disease control. To successfully manage this viral pathogen long into the future, management practices focus on preventing the disease by planting uninfected seed, reducing the proximity of seed crops to commercial acreage, and reducing the likelihood that viruliferous aphids will feed on the crop through early vine killing. Application of insecticide will seldom achieve any practical or permanent control of PVY. The systemic neonicotinoid insecticides have proven invaluable in controlling many of the potato colonizing aphid species (e.g., green peach and potato aphid), but because many of the aphids responsible for PVY spread are transient (non-colonizing), insecticides do not play a large part in the recommended PVY management program.     

Insect Vector Behavior in Potatoes: Interrupting Transmission.

Gina Angellela, USDA ARS

Understanding insect vector behavior is critical for the effective management of insect-vectored plant pathogens. This is especially important regarding pathogens with differing modes of transmission such as observed among aphid-vectored viruses (i.e. nonpersistent, semi-persistent, or persistent). This talk will focus on the behavior of persistent aphid-vectored virus transmission. Efforts are currently underway to screen various insecticides for behavioral effects on aphids and their interactions with potato plants, relative to the transmission of potato leafroll virus (PLRV). Our goal is to identify additional chemical management options for the prevention or reduction of PLRV infection in potato production.

Economic Management of Insects that Vector Diseases of Potato

Tim Waters, Washington State Univ.    

               Potato producers are under pressure to deliver potatoes to customers that are free of internal defects including discoloration that can result from viruliferous insects feeding upon potato plants. As such, growers have come to rely on timely application of insecticides to reduce the likelihood of such damage occurring to their crop. Regulation and customer demands have resulted in changes to the class of insecticides that growers are able to utilize to mitigate damage from viruliferous insects. Newer classes of insecticides tend to be slower acting, narrower in spectrum, more expensive, and shorter in residual than their predecessors. Therefore, growers must be better able to identify insect threats accurately and quickly in their fields to manage them effectively with these newer classes of insecticides. We have developed strategies to utilize the new classes of insecticides for management of insects that vector diseases of potato. Implementation of these strategies will be discussed in detail including consideration of future use patterns of insecticides to avoid economic losses by insect vector disease in potatoes.           Tim Waters, Madeline Spets, and Ashely Spralding, Washington State University Extension

A Tricky Trio: PMTV, S. subterranea, and Potato Powdery Scab Disease

Vamsi Nalam, Colorado State Univ.     

               Potato powdery scab, a disease caused by the soil-borne fungus Spongospora subterranea f. sp. subterranea (S. subterranea), is a major threat to potato quality worldwide. However, limited knowledge exists regarding the potato mop-top virus (PMTV), a single-stranded RNA virus transmitted by S. subterranea, its interaction with the vector, and their combined virulence in the U.S. This study addresses this knowledge gap by investigating PMTV genetic diversity and S. subterranea population structure. Despite limitations in PMTV detection methods, we sequenced seven isolates and identified a single isolate with a unique mutation potentially linked to reduced virulence. Additionally, our work suggests variations within S. subterranea populations across the U.S. Surprisingly, low genetic diversity in PMTV itself did not impact virulence in controlled settings. Instead, the origin of S. subterranea inoculum played a more significant role. Furthermore, we developed new diagnostic primers for each RNA segment of the tripartite PMTV genome. Interestingly, the TGB segment was found in the highest abundance. Finally, our research revealed a lack of correlation between PMTV and S. subterranea levels in soil samples. However, a clear relationship was observed in plant bioassays, suggesting the influence of environmental factors and potato cultivar on disease development. These findings contribute valuable insights into PMTV diversity and S. subterranea virulence in the context of U.S. potato powdery scab, paving the way for future management strategies.       

Jennifer Rushton, Vamsi J Nalam, Colorado State University