Potato Virus Y Spread Research Articles

Effects of Climate Change on the Spread and Severity of Potato Virus Y: An In-depth Examination

Potatoes are a cornerstone of global agriculture and a fundamental component of diets worldwide, with plant viruses accounting for nearly half of the emerging crop epidemics. Among these, Potato Virus Y (PVY) poses a formidable challenge to potato farming, leading to significant economic repercussions and threats to food security. Understanding the influence of climate on PVY is pivotal in tackling this viral menace. Climatic conditions, including temperature, precipitation, and humidity, play a key role in the behavior of aphids, the primary vectors of PVY, thereby impacting the disease's prevalence in potato fields. With climate change modifying these key weather variables, there's a looming risk of enhanced PVY spread and a shift in its geographical presence. Recognizing and adapting to these climate-induced changes is vital for formulating effective strategies and sustainable practices to counter PVY's effects, safeguarding potato crops from this major viral threat. This analysis delves into the complex dynamics between climate change and PVY, focusing on how changes in weather patterns influence the virus's behavior and impact, with the aim of enhancing our preparedness and response to this agricultural challenge.

MATHEMATICAL MODEL OF POTATO VIRUS Y DISEASE SPREAD WITH OPTIMAL CONTROL

Potato virus Y (PVY) is an aphid-borne plant virus that causes substantial yield losses in potato production. Control measures of the viral infection are both limited and expensive. A proper use of mixed-cropping strategy can reduce the spread of PVY. In this paper, we formulate and analyze a mathematical model of PVY spread in a mixed-cropping system. Then, we extend the model to an optimal control problem by considering use of mineral oil, insecticide and farmer’s level of field inspection for infected plants. The analytic results show that the basic reproduction number ℜ0, a threshold parameter that decides properties of the dynamics. The disease free equilibrium is stable if ℜ0 < 1 and unstable when ℜ0 > 1. It is found that ℜ0, and hence, the disease dynamics is highly sensitive to the representative parameters of density the non-host plant and its quality in attracting vectors. The model exhibits forward bifurcation at ℜ0 = 1. The study of optimal control problem suggests that mixed-cropping combined with either mineral oil or insecticide is the best to control the disease. Furthermore, simulation results show that mixed-cropping can be used as an alternative strategy and can reduce the need of mineral oil or insecticide.

Comparison of Mineral Oil, Insecticidal, and Biopesticide Spraying Regimes for Reducing Spread of Three Potato virus Y Strains in Potato Crops.

In-field management of Potato virus Y (PVY) faces challenges caused by the changing availability and environmental acceptability of chemical agents to control aphid vectors of the virus and by proliferation of PVY strains with different symptoms and rates of spread. From 2018 to 2020, foliar spray treatments were compared in field experiments in New Brunswick, Canada, to measure effectiveness at reducing spread of PVYO, PVYN:O, and PVYNTN strains. Mineral oil, insecticide, combined oil and insecticide spray, and a biopesticide (i.e., LifeGard WG) were compared. Insecticide-only and mineral oil-only treatments were not effective, but several combined oil and insecticide treatments and biopesticide treatments significantly reduced PVY spread. The biopesticide was proportionately more effective with recombinant PVYN:O and PVYNTN strains, possibly by exciting the plant's hypersensitive resistance response, caused naturally only in cultivar 'Goldrush' by PVYO. Pesticide residue analysis showed that mineral oil increased the retention of pyrethroid insecticide in the potato foliage longer than with insecticide applied alone, which may explain the beneficial synergistic effect of combined sprays for reducing PVY spread. Tuber yields were generally unchanged in chemical insecticide treatments but were slightly lower in biopesticide treatment. The cost per PVY treatment was competitive across all effective treatments, including biopesticide; however, there was some revenue loss from lower yield with the biopesticide. This biopesticide is certified organic, however, and thus a small premium on the price for organic production could offset this yield deficit.

A one-step reverse transcription recombinase polymerase amplification assay for lateral flow-based visual detection of PVY

Potato virus Y (PVY) is an abundant and damaging virus which reduces crop yield and marketability. Accurate detection of this economically important virus both in-field and in seed potatoes is considered essential in the control of PVY spread. Current detection methods are focused on immunodetection and PCR-based methods, however, identification of PVY through isothermal amplification is a promising avenue for developing accessible, on-site diagnostics with quick turnaround times. In this work, a rapid recombinase polymerase amplification assay was developed which could readily amplify PVY nucleic acids with good sensitivity and specificity. Additionally, this assay was shown to be capable of amplification directly from RNA in a one-step amplification process, without the need for prior reverse transcription. The assay was coupled with lateral flow technology to provide a rapid visual confirmation of amplification. This nucleic-acid lateral flow immunoassay could feasibly be employed in-field, or at any location where testing is required, to aid in the detection and control of PVY.

Simulation modelling of potato virus Y spread in relation to initial inoculum and vector activity

Potato virus Y (PVY) is a non-persistent virus that is transmitted by many aphid species and causes significant damage to potato production. We constructed a spatially-explicit model simulating PVY spread in a potato field and used it to investigate possible effects of transmission efficiency, initial inoculum levels, vector behavior, vector abundance, and timing of peak vector activity on PVY incidence at the end of a simulated growing season. Lower PVY incidence in planted seed resulted in lower virus infection at the end of the season. However, when populations of efficient PVY vectors were high, significant PVY spread occurred even when initial virus inoculum was low. Non-colonizing aphids were more important for PVY spread compared to colonizing aphids, particularly at high densities. An early-season peak in the numbers of noncolonizing aphids resulted in the highest number of infected plants in the end of the season, while mid- and late-season peaks caused relatively little virus spread. Our results highlight the importance of integrating different techniques to prevent the number of PVY-infected plants from exceeding economically acceptable levels instead of trying to control aphids within potato fields. Such management plans should be implemented very early in a growing season.

Evidence of Potato virus Y Spread through Post-Emergence Management Practices in Commercial Potato Fields

Potato virus Y (PVY) transmission was studied in six commercial potato fields in 2015 and 2016 in New Brunswick, Canada. Plants emerged from PVY-positive tubers, or PVY-free plants that were artificially inoculated with PVY shortly after emergence, were used as PVY inoculum plants in the study. In all trials, equal numbers of PVY inoculum plants from each of three strains common in the region, PVYO, PVYN:O and PVYNTN, were used. PVY inoculated into tractor-traffic rows showed 2 to 7 times as much PVY spread to previously virus-free plants by the end of the season (up to 48.5% in one tractor row, compared to a maximum of 16.3% in a distant control row unaffected by tractor traffic). Evidence supporting a hypothesis that tractor traffic enhances PVY transmission through aphid disturbance was observed by PVY spread in both directions along the rows, not biased in the direction of tractor travel, and that the ratio of spread of the three strains was nearly indentical in control and tractor rows. However, the lack of spread to immediately adjacent rows, and statistically significant spatial pattern matching the circumference of tractor wheels specific to each field support the hypothesis that direct mechanical transmission of wounded plant sap could also be a factor in the enhanced PVY transmission.

Differential Spread of Potato virus Y (PVY) Strains O, N:O and NTN in the Field: Implications for the Rise of Recombinant PVY Strains in New Brunswick, Canada

Potato virus Y (PVY) is a major cause of yield and quality loss in potato crops worldwide. Recently, populations of PVY strains have shifted dramatically toward recombinant strains such as PVYNTN and PVYN:O. A 2010 to 2016 survey of PVY strains in commercial fields of New Brunswick (NB), Canada, and five field trials tracking PVY spread in NB and Manitoba, were conducted to study the current status of PVY strains and their relative rates of spread. In NB, PVYO dropped from 82% of infections in 2010 to 14% in 2016, replaced mostly by PVYNTN (64%) and PVYN:O (22%).In field trials with Russet Burbank and Gold rush varieties, PVYNTN spread most effectively compared to PVYN:O and PVYO. Strain-specific PVY spread varied with the potato variety, possibly due to selective PVYO resistance in Goldrush, mostly expressed at the plant-to-plant transmission level with little difference in transduction to tubers in infected plants. Relevance of in-field differences in spread of strains to changes in regional PVY populations, and potential mechanisms responsible, are discussed.

Hop/Sti1 - A Two-Faced Cochaperone Involved in Pattern Recognition Receptor Maturation and Viral Infection.

Perception of pathogens by host pattern recognition receptors (PRRs) or R proteins is a prerequisite to promote successful immune responses. The Hsp70/Hsp90 organizing protein Hop/Sti1, a multifunctional cochaperone, has been implicated in the maturation of a receptor-like kinase (RLK) necessary for chitin sensing. However, it remains unknown whether Hop/Sti1 is generally participating in PRR genesis. Using RNA-interference (RNAi), we silenced Hop/Sti1 expression in Nicotiana tabacum to gain further insight into the role of the cochaperone in plant defense responses. As expected, transgenic plants do not respond to chitin treatment anymore. In contrast to this, trafficking and functionality of the flagellin PRR FLS2 were unaltered, suggesting a selective involvement of Hop/Sti1 during PRR maturation. Furthermore, Hop/Sti1 was identified as a cellular determinant of Potato virus Y (PVY) symptom development in tobacco, since PVY was able to accumulate to near wild-type level without provoking the usual veinal necrosis phenotype. In addition, typical antiviral host defense responses were suppressed in the transgenic plants. These data suggest that perception of PVY is dependent on Hop/Sti1-mediated receptor maturation, while viral symptoms represent a failing attempt to restrict PVY spread. In addition, Hop/Sti1 colocalized with virus-induced membrane aggregates in wild-type plants. The retention of Hop/Sti1 in potential viral replication complexes suggests a role during viral translation/replication, explaining why RNAi-lines do not exhibit increased susceptibility to PVY. This study provides evidence for a dual role of Hop/Sti1 in PRR maturation and pathogen perception as well as in promoting viral proliferation.

Control of potato virus Y (PVY) in seed potatoes by oil spraying, straw mulching and intercropping

Potato virus Y (PVY) is the potato virus with the highest economic impact on seed potato production. Insecticides are efficient in controlling aphids, which are the vectors of this virus, but rarely limit virus spread in the field. Straw mulching and mineral oil spraying are known as alternatives to insecticides to reduce PVY incidence, but important year‐to‐year variation in efficacy has been observed with both of these techniques. Preliminary studies revealed the efficacy of intercropping in controlling PVY spread, but more data are needed to validate this observation. A four‐year field trial was conducted in Switzerland to assess the potential synergistic effect of combining mineral oil spraying with straw mulching to increase the protection of seed potato crops against PVY spread. Furthermore, the efficacy of intercropping with oat and hairy vetch was examined as a novel way to control in‐field PVY spread. The present work demonstrates that the modes of action of mineral oil and straw mulching are complementary and reduce the year‐to‐year variation observed with oil and straw when used alone as PVY control agents. The results also demonstrate the efficacy of intercropping for the control of PVY, and the mode of action of this novel control method is discussed. Overall, this work shows that it is possible to increase the protection of potato fields against PVY spread by combining control strategies with different modes of action that complement each other, such as mulching, oil spraying and intercropping.

Effectiveness of Combined Use of Mineral Oil and Insecticide Spray in Reducing Potato Virus Y (PVY) Spread under Field Conditions in New Brunswick, Canada

In the 2014 and 2015 crop seasons, the efficacies of different types, rates and combinations of mineral oil and insecticide foliar sprays for reducing Potato virus Y (PVY) spread were tested in controlled field trials in New Brunswick (NB), Canada. Experimental plots were planted with certified PVY-free Goldrush, supplemented with known virus-infected seed to raise PVY inoculum to 2.3% and 3% at the beginning of the 2014 and 2015 seasons, respectively. Treatments consisted of mineral oil-only sprays at different application rates, insecticide-only sprays of differing numbers, and several combined mineral oil and insecticide spray regimes, all compared to a no-spray control treatment. PVY spread to 18% (2014) and 22% (2015) of initially virus-free plants in no-spray control plots, with significant reductions observed in PVY spread in several treatments. Greatest PVY reductions, as low as 4% (2014) and 12% (2015), were in combined mineral oil and insecticide spray treatments, followed by oil-only sprays; while insecticide-only sprays did not significantly reduce PVY spread. As well as measuring PVY spread to marked test plants and randomly collected post-harvest tuber sample from the plots, exhibited similar treatment pattern for PVY incidence. Multiple logistic regression modeling confirmed the relative efficacy of combined oil and insecticide sprays for reducing PVY spread, while accounting for variable inoculum and aphid factors. Modeling also highlighted the importance of planting low-PVY seed initially, and of early application of foliar sprays. Local best management practice recommendations for reduction of in-field PVY spread were discussed.

Crop Management Practices and Reduction of On-Farm Spread of Potato virus Y: a 5-Year Study in Commercial Potato Fields in New Brunswick, Canada

In this study, on-farm within-season spread of Potato virus Y (PVY) was measured in 56 seed, processing and tablestock potato fields in New Brunswick, Canada between 2010 and 2014. These represented 13 potato varieties, managed by 16 growers employing a wide range of PVY control techniques. Many aspects of management techniques were quantified, as well local aphid abundances and climatological data. PVY spread, measured in leaves and tubers (by ELISA and RT-PCR), was tracked through the season in individually marked plants. Over the five seasons under study, on-farm PVY spread overall has declined substantially. Across all 56 fields, however, it has varied widely, from 10 fields not showing any spread during the crop season, up to as high as 76 % spread in one 2012 field. Factors correlated with increased PVY spread included seed-borne PVY inoculum planted in the field, aphid abundance early in the season, and to a lesser degree temperatures in July and over the preceding winter. Factors correlated with decreased spread included numbers of foliar mineral oil and insecticide sprays (especially of the lambda-cyhalothrin and flonicamid types), later crop planting and earlier first spraying dates. A mid-season leaf test for PVY was shown to be strongly indicative of ultimate PVY spread at harvest, and may prove a useful test in advising growers. A set of locally-relevant best management practices based on these results is discussed.

The Use of Mineral Oil in Potato Protection: Dynamics in the Plant and Effect on Potato Virus Y Spread

The focus of this study was to evaluate two mineral oils (Superior 70 and Vazyl-Y) in reducing the seasonal spread of Potato Virus Y (PVY). Three concentrations of oil (0, 5, and 10 L ha−1 of Superior 70; 0, 7.5, and 15 L ha−1 of Vazyl-Y) and three spray regimes for both oils (every 3–4, 7, and 10–11 days) were tested. Two weeks after top-kill, two tubers from each of 49 plants free of virus at emergence were harvested from treatment plots, sprouted, and tested for PVY with enzyme-linked immunosorbent assay (ELISA). Results revealed that in the case of Superior 70, PVY spread in mineral oil treated plots ranged from 2.1 to 12.2 %, while in the control plots it ranged from 20.4 to 37.7 % across three cultivars. In the case of Vazyl-Y, PVY spread in mineral oil treated plots ranged from 2.1 to 26.5 %, while in the control plots it ranged from 49.9 to 85.7 % across three cultivars. These data show that there was a significant reduction in PVY due to spray of mineral oils. In addition, mineral oil was quantified in plants from the Superior 70 treated and the control plots to understand the dynamics of mineral oil during the season. While there was little to no oil measured in the leaves at the early stages of plant growth, a considerable amount of mineral oil was detected close to plant maturity. A basic model of the concentration of oil in the treated foliage was formulated to confirm our understanding of the factors at play. The model could explain from 50 to 90 % of the variation in oil content observed in the field. Plant growth and size are important factors affecting oil content in mineral oil treated foliage.

Effects of Crop Management Practices on Current-Season Spread of Potato virus Y.

The current-season spread of Potato virus Y (PVY) was monitored in 19 fields under various management practices in New Brunswick, Canada, through the 2011 and 2012 growing seasons. The focus of this study was to evaluate the role of seedborne PVY inoculum, aphid vector abundance, and the numbers, timing, and types of insecticide and mineral oil sprays, and to confirm the reliability and forecasting capacity of midseason PVY testing. In each field, 100 to 110 virus-free plants were identified shortly after emergence and were assessed four times from early July to early September (after top-kill) with enzyme-linked immunosorbent assay (ELISA) and reverse-transcription polymerase chain reaction (RT-PCR) to track PVY spread. In addition, tubers harvested during development in August and after top-kill were grown-out in the greenhouse for ELISA testing. PVY spread to selected virus-free plants varied widely, ranging from 0 to 76.2% across all studied fields. Of the 19 fields over two seasons, 10 fields were planted with no detectable seedborne PVY, and they showed 0 to 8.7% (mean 2.9%) PVY spread by harvest. The remaining nine study fields with 0.9 to 5.8% seedborne PVY showed 1 to 76.2% (mean 15.2%) PVY spread by harvest. PVY spread was detected in most fields during midseason testing with ELISA and RT-PCR; all tests correlated well with final PVY rates after top-kill, though RT-PCR detection in developing tubers was most sensitive and correlated. Logistic regression modeling was used to identify major factors in PVY spread, including seedborne PVY, early-season aphid abundance, and the numbers of insecticide and mineral oil sprays. The best-fitting model, constructed using these factors as well as a measurement of July PVY incidence (ELISAJuly), strongly explained PVY spread by harvest, with the most significant management factor being the number of mineral oil sprays supplemented with insecticide used during the growing season. A similar model fitted without the ELISAJuly did not adequately predict ultimate PVY spread. The analysis suggests that mineral oil alone was effective at lowering PVY spread, and more effective when combined with insecticide, particularly when used early in the season. No evidence was found for differences in PVY spread across the eight cultivars used or across the range of mineral oil application rates, whereas some evidence was found for differences in the effectiveness of different insecticide types.

Continuous and Emerging Challenges of Potato virus Y in Potato

Potato virus Y (PVY) is one of the oldest known plant viruses, and yet in the past 20 years it emerged in the United States as a relatively new and very serious problem in potato. The virus exists as a complex of strains that induce a wide variety of foliar and tuber symptoms in potato, leading to yield reduction and loss of tuber quality. PVY has displayed a distinct ability to evolve through accumulation of mutations and more rapidly through recombination between different strains, adapting to new potato cultivars across different environments. Factors behind PVY emergence as a serious potato threat are not clear at the moment, and here an attempt is made to analyze various properties of the virus and its interactions with potato resistance genes and with aphid vectors to explain this recent PVY spread in potato production areas. Recent advances in PVY resistance identification and mapping of corresponding genes are described. An updated classification is proposed for PVY strains that takes into account the most current information on virus molecular genetics, serology, and host reactivity.

Modulation of Aphid Vector Activity by Potato virus Y on In Vitro Potato Plants.

The effects of the infection of potato (Solanum tuberosum) plants by the nonpersistent Potato virus Y (PVY) were studied on the host plant colonization behavior of different colonizing (Myzus persicae) and noncolonizing (Aphis fabae, Brevicoryne brassicae, and Sitobion avenae) aphid species. The underlying questions of this study were to know how aphids respond when faced with PVY-infected plants and whether plant infection can modify the aphid behavior involved in PVY spread. Short-range orientation behavior was observed using a dual-choice set-up and aphid feeding behavior was monitored using the electrical penetration graph technique. None of the aphid species discriminated between healthy and PVY-infected plants. Nevertheless, most individuals of M. persicae landed on and probed only in one plant whereas noncolonizing aphid species exhibited interplant movements. Study of the aphid feeding behavior showed that PVY infection essentially modified phloem and xylem ingestion. M. persicae and S. avenae exhibited an increased duration of phloem phases on PVY-infected plants whereas A. fabae showed a decreased duration of phloem phases that benefited from an increased duration of xylem ingestion phases. None of these parameters were changed in B. brassicae. These data present evidence that aphids can respond to plants infected by nonpersistent viruses. Such behavioral modifications are discussed within the context of PVY spread in potato crops.

Planter Skips and Impaired Stand Favors Potato Virus Y Spread in Potato

High incidence of virus infection in potato crops can cause stand loss, reduced yields, and undersized tubers, leading to reduced quality and downgrading or rejection of potato seed lots. Initial colonization of potato fields by aphid vectors of potato viruses is predominately concentrated on field margins. In fields with poor stands, there are gaps in the crop canopy that can be attractive to alighting aphids. Thus, occurrence of stand gaps could render ineffective any pest management tactic that exploits the colonization behavior of aphids, such as barrier crops or reflective mulches. Field studies were undertaken to determine if the occurrence of localized stand gaps in potato fields would increase potato virus Y (PVY) infections and, if so, whether there was a relationship between gap size and PVY spread. PVY infection was 13% around stand gaps of ≤0.6 m2, while PVY infection was 29% around gaps ≥0.6 m2. Our results indicate that a stand gap equivalent to a loss of three or more consecutive plants within a row favored PVY spread. Trials were conducted to compare effects of roguing (physical removal of plants), seeding with oats to reduce potato canopy/soil contrast, and insecticide applications to gaps on PVY spread. Roguing, seeding gaps with oats and insecticides did not prevent PVY spread. This research indicates that suboptimal plant stands increase PVY incidence and may be contributing to the current PVY epidemic.

Solanum elaeagnifolium, a potential source of Potato virus Y (PVY) propagation*

In the context of an epidemiological study on Potato virus Y (PVY) in potato crops, Solanum elaeagnifolium Cav. was included in the weeds prospected. Surveys were carried out in four seed potato areas: Cap Bon, Manouba, Jendouba and Kairouan. S. elaeagnifolium was found in all areas, except Cap Bon. Virus‐like symptoms were observed on some S. elaeagnifolium plants in the field, i.e. leaf mottling and curling. Aphids were collected on these plants and were identified as Myzus persicae and Aphis fabae, both known to colonize potatoes and to transmit the standard PVYN isolate with transmission efficiencies of 95% and 43%, respectively. Forty‐seven plant samples were tested with ELISA for the presence of PVY. Positive reactions were obtained from 2/6, 5/18, 8/23 samples collected in Manouba, Jendouba and Kairouan, respectively. Virus transmission was carried out using M. persicae as vector from two samples of each region onto plantlets of Nicotiana tabacum cv Xanthi. All inoculated plantlets displayed typical symptoms of the PVYN strain group, confirmed by serological testing using specific antibodies. This is the first report of a PVY natural infection on S. elaeagnifolium in Tunisia. The abundance of this weed, its over‐wintering status and the high rate of PVY‐infected plants (31.9%) allow us to deduce that S. elaeagnifolium must be considered a reservoir species of PVY under natural conditions in Tunisia and probably in other Mediterranean countries. The presence of efficient aphid vectors of PVY on this weed in crops is additional evidence that S. elaeagnifolium may become a problem by acting as a source plant for PVY spread in potato crops.

Low-level jet streams associated with spring aphid migration and current season spread of potato viruses in the U.S. northern Great Plains

Green peach aphid, Myzus persicae (Sulzer), is the principal and possibly sole vector of Potato leafroll virus (PLRV) and a key vector of Potato virus Y (PVY) in the U.S. northern Great Plains. Current season spread of PLRV and PVY in seed potato depends primarily on flight activity of winged aphids and the availability of virus inoculum. M. persicae does not overwinter outdoors in the northern Great Plains, populations are reestablished each year by spring immigrants from the south. The objective of this research was to relate spring low-level jet (LLJ) streams to intensity of M. persicae flight activity and current season spread of PLRV and PVY. Synoptic weather maps were used to identify LLJ events that could have brought aphids into the northern Great Plains and to record the timing and duration of each event from 1 May to 30 June. HYSPLIT (Hybrid Single-particle Lagrangian Integrated Trajectory), a trajectory analysis model developed by the National Oceanic and Atmospheric Administration and Australian Bureau of Meteorology, was used to track pathways of air particles to their source. Captures of M. persicae and other potential vector species by a regional aphid trapping network ( Aphid Alert) from 1992 to 1994 and 1998 to 2003 were used as measures of aphid flight activity. Results from winter grow-outs of the Minnesota Seed Potato Certification Program were used as measures of available PLRV and PVY inoculum. As a possible surrogate for aphid flight activity we used data on spring wind events to predict current season seed lot rejections due to PLRV and PVY. Statistical models were developed relating frequency and duration of spring wind events to subsequent M. persicae abundance and severity of PLRV and PVY spread in the northern Great Plains. Results showed that the cumulative LLJ duration fit best with cumulative M. persicae capture through the first week of August ( R 2 ranging from 0.597 to 0.883), and the current season spread of PLRV fit best with inoculum and cumulative M. persicae capture through the first week of August ( R 2 = 0.75, P = 0.015). LLJ duration did not reliably predict seasonal abundance of PVY vectors other than M. persicae. The model for prediction of PVY using LLJ duration and PVY inoculum was considerably less reliable ( R 2 = 0.30, P = 0.34) although using both M. persicae capture through the first week of August and PVY inoculum fit better ( R 2 = 0.39, P = 0.231).

Seasonal Abundance of Aphid Vectors of Potato Virus Y in the Red River Valley of Minnesota and North Dakota

An epidemic of aphid-transmitted potato virus Y (PVY) in seed potato grown in the Red River Valley of Minnesota and North Dakota was the reason we began a study to determine which aphid species were found in traps placed near potato fields. Knowledge of which aphid species are present and which of these are known vectors of PVY is needed to develop management strategies that minimize virus spread. The spread of PVY to healthy indicator plants and captures of alate aphids in tile traps were monitored weekly for 3 yr consecutively (1992-1994) throughout the Red River Valley. Thirty-four aphid species were identified from green and yellow tile traps in 1992, 25 in 1993, and 26 in 1994. Yellow tile traps caught significantly more aphids overall than green tile traps and were significantly preferred by Aphis helianthi Monell, Capitophorus elaeagni (del Guercio), and Rhopalosiphummaidis (Fitch). Intervals of greatest aphid capture in green traps were generally between mid-July and mid-August at all sites in all 3 yr. Aphid captures at all sites were 3-25 times greater in 1992 and 1994 than in 1993. PVY infection of indicator plants exposed at the trapping sites also was greater in 1992 (25 plants) and 1994 (18 plants) than in 1993 (2 plants). Eighty-nine percent of PVY spread to indicator plants occurred between 8 July and 19 August. Eight species comprised 89.9% of the aphids collected in green traps during intervals of PVY transmission to indicator plants: Acyrthosiphon pisum (Harris), pea aphid; A. helianthi; C. elaeagni; Lipaphis erysimi (Kaltenbach), turnip aphid; R. maidis, com leaf aphid; R. padi (L.), bird cherry-oat aphid; Schizaphis graminum (Rondani), greenbug; and Sitobion avenae (F.), English grain aphid. Seven of these species were previously known PVY vectors. We found that A. helianthi transmitted PVY with low efficiency under greenhouse conditions. The 8 most common aphid species were associated with crops and weeds common in the Red River Valley. Our data suggest that although the relative importance of individual PVY vectors varies from year to year and location by location, total aphid captures may be the best indicator of the risk of PVY spread.

Control of aphid-borne potato virus Y in potatoes with oil emulsions

Tests were made at Presque Isle, Maine, from 1963 through 1965 to measure the effect of oil sprays on the spread of potato virus Y (PVY) in Green Mountain potatoes. In 1963, 4 weekly applications of a 1% mineral oil emulsion at 1.25 gal oil/acre(4.71/.41 ha) did notaffect significantly (P = 0.05) the spread of PVY. In 1964, the 64% control of PVY spread from 5 weekly applications of mineral oil emulsion at 1.25 gal/acre was not significantly different at that level from the 55% control from 5 weekly applications of the oil emulsion at 2.5 gal/acre (9.5 1/.41 ha). Three or 5 weekly applications of an alkylated naphthalene (Velsicol AR-60®) spray at 1.25 gal/acre significantly increased spread of PVY compared to that from 5 applications of the oil at 1.25 or at 2.5 gal/acre. In 1965, from 69 to 75% control of PVY spread resulted from 6 weekly applications of a paraffin oil emulsion at 2.5 gal/acre. The percent spread from the 6 weekly applications was smaller, but not significantly so (P = 0.05), than from 3 weekly applications made during the first half of the same 6-week period. In these tests, relatively light spread of PVY occurred, and control of spread was rather variable but the results indicate that oil emulsion sprays offer promise for protecting potato plants from PVY infection.