Barley Yellow Dwarf Luteovirus Research Articles

Diversity and Composition of Viral Communities: Coinfection of Barley and Cereal Yellow Dwarf Viruses in California Grasslands

Most species host multiple pathogens, yet field studies rarely examine the processes determining pathogen diversity within a single host or the effects of coinfection on pathogen dynamics in natural systems. Coinfection can affect pathogen transmission and virulence. In turn, coinfection can be regulated within hosts by interactions such as cross-protective immunity or at broader spatial scales via vector distributions. Using a general model, we demonstrate that coinfection by a group of vectored pathogens is highest with abundant generalist vectors and weak cross-protection and coinfection-induced mortality. Using these predictions, we investigate the distribution of five coexisting aphid-vectored, viral pathogens (barley and cereal yellow dwarf luteoviruses and poleroviruses) in a native perennial grass (Elymus glaucus) in both space (700 km) and time (4 years). Observed coinfection rates were much higher than expected at random, suggesting that within-host processes exerted weak effects on within-host pathogen diversity. Covariance among viruses in space and time was highest for viral species sharing a vector. Temporal correlation arose from the synchronous invasion of two viruses transmitted by a shared aphid species. On the basis of our modeling and empirical results, we expect that factors external to individual hosts may affect the coinfection dynamics in other communities hosting vectored pathogens.

Variation in Barley Yellow Dwarf Virus Transmission Efficiency by Rhopalosiphum padi (Homoptera: Aphididae) after Acquisition from Transgenic and Nontransformed Wheat Genotypes

The effects of different acquisition access periods (AAPs) and inoculation access periods (IAPs) on the transmission efficiency of barley yellow dwarf luteovirus (BYDV) by Rhopalosiphum padi (L.) (Homoptera: Aphididae) after feeding on transgenic or nontransformed wheat, Triticum aestivum L., genotypes were studied. Three wheat genotypes were tested as virus sources: virus-susceptible 'Lambert' and 'Lambert'-derived transgenic lines 103.1J and 126.02, which express the BYDV-PAV coat protein gene. Lower virus titers were measured in BYDV-infected transgenic plants compared with Lambert. No significant differences in transmission efficiency were detected for R. padi after varying IAPs, regardless of genotype. Transmission efficiency increased with an increase in AAP in all genotypes tested. However, AAPs ranging from 6 to 48 h on Lambert resulted in significantly greater transmission efficiency than similar periods on transgenic 103.1J. Maximum transmission efficiency (70%) was observed after a 48-h AAP on Lambert, whereas the same AAP on 103.1J and 126.02 resulted in a significantly lower transmission efficiency (57%). Contrasts were used to compare the rates of transmission and the theoretical maximum transmission percentage among the different wheat genotypes serving as virus sources. Both parameters were significantly different among genotypes, indicating that viral acquisition from each genotype resulted in a unique pattern of virus transmission by R. padi. The lowest rate of virus transmission after an AAP was observed on 103.1J compared with 126.02 or Lambert. This is likely associated with a lower virus titer in 103.1J. This is the first report of transgenic virus resistance in wheat affecting the transmission efficiency of a virus vector.

Volatile Cues Influence the Response ofRhopalosiphum padi(Homoptera: Aphididae) to Barley Yellow Dwarf Virus–Infected Transgenic and Untransformed Wheat

The attractiveness of Barley yellow dwarf luteovirus (BYDV)–infected wheat plants to Rhopalosiphum padi L. was evaluated under laboratory conditions. Two untransformed wheat varieties, virus-susceptible Lambert and virus-tolerant Caldwell, and one transgenic wheat genotype (103.1J) derived from Lambert and expressing the BYDV coat protein gene, were tested in three bioassays. First, R. padi responses to BYDV-infected or noninfected Lambert and Caldwell were evaluated. Significantly more aphids settled onto virus-infected than noninfected plants when aphids were able to contact the leaves. Second, aphid responses to headspace from virus-infected or noninfected Lambert and Caldwell were tested. Significantly more aphids congregated on screens above headspace of BYDV-infected plants than above headspace of noninfected plants of both varieties. Third, aphid responses to headspace from virus-infected or noninfected and sham-inoculated (exposed to nonviruliferous aphids) Lambert and 103.1J plants were examined. Significantly more aphids congregated on screens above BYDV-infected than above noninfected or sham-inoculated Lambert. No significant differences in R. padi preferences for headspace above BYDV-infected compared with noninfected or sham-inoculated 103.1J plants were observed. The concentration of volatiles extractable from whole plant headspace was greater on BYDV-infected Lambert than on BYDV-infected 103.1J, noninfected, or sham-inoculated plants of either genotype. This is the first report of volatile cues associated with BYDV infection in wheat plants influencing the behavior of the vector R. padi. Additionally, these findings show for the first time that transgenic virus resistance in wheat can indirectly influence the production of volatiles making virus-infected plants less attractive or arrestant to aphids than are infected untransformed plants.

Occurrence of cereal viruses on wheat in Tekirdag, Turkey

A survey for detection of barley yellow dwarf luteoviruses (BYDV-PAV and BYDV-MAV), cereal yellow dwarf polerovirus (CYDV-RPV), barley stripe mosaic hordeivirus (BSMV), wheat dwarf monogeminivirus (WDV) and brom mosaic bromovirus (BMV) was carried out during May 2003 covering seven cereal-growing counties of Tekirdag, Turkey. Two hundred sixty (260) wheat samples with yellowing, stunting, or striping were collected from 26 wheat fields. These samples were tested for the presence of six viruses by ELISA using polyclonal antisera. Serological tests showed that six tested viruses were present in Tekirdag, Turkey. Among the tested viruses, BYDV-MAV was the most commonly detected (25% of the 260 wheat samples), followed by BYDV-PAV (22.3%), WDV (16.5%), CYDV-RPV (8.5%), BMV (3.1%) and BSMV (1.5%). This study revealed the presence of six viruses in wheat fields in Tekirdag and reported for the first time BSMV and BMV on wheat in Turkey.

Use of remote sensing to detect virus infected wheat plants in the field

Applicability of remote sensing to detect virus infection of wheat was studied under field conditions. The experiments were carried in a wheat variety experimental field in Szeged, Hungary, continuously exposed to natural infection by viruses from sowing to harvest. Plants were evaluated for virus infections by visual inspection and aerial photography, and viral contents were quantitated by DAS-ELISA of randomly taken samples. Analysis of the results showed a direct relationship between the extent of yellowing of the leaves and the rate of Wheat dwarf bigemovirus (WDV) and Barley yellow dwarf luteovirus (BYDV) infection, but not with that of other wheat pathogenic viruses, such as Wheat streak mosaic tritimovirus (WSMV), Brome mosaic bromovirus (BMV), and Barley stripe mosaic hordeivirus (BSMV).

Multiple virus infection of wheat in South Hungary

Incidences of multiple virus infections of wheat genotypes were studied in South Hungary over a five-year period (1994-1999). The viruses detected serologically were: Barley yellow dwarf luteovirus (BYDV), Barley stripe mosaic hordeivirus (BSMV), Brome mosaic bromovirus (BMV), Wheat dwarf bigemovirus (WDV) and Wheat streak mosaic tritimovirus (WSMV). Surprisingly BYDV was found less frequently in comparison to BRSMV, BSMV and WDV. It suggests that in this area BYDV is economically less important than other viruses infecting cereals. In many individual plants 2-5 different viruses were identified. The abundant multiple infections of several virus species suggest that the estimation of natural viral infection cannot be based only on the analysis of a single virus species. On the other hand the development of multiple resistance in wheat seems to be essential to defend the plants against the most important viruses in a given area.

VIRAL DISEASES ON CEREALS IN CENTRAL HUNGARY

In recent years viral diseases have become more frequent on cereals in Hungary. In the breeding nursery of the Martonvásár Institute, which contains stocks with very diverse genetic backgrounds, wheat suffered major attacks by viruses in 1972, 1976, 1980, 1981, 1982, 1986, 1990, 1996 and 1998. The winter barley plots incurred great damage in 1989 and 1990, while a large proportion of the durum wheat was destroyed in 1996. In 1982 barley yellow dwarf virus caused an epidemic in Fejér County and on many farms the damage was so great that the fields had to be ploughed up. The following nine viruses, which impose a threat to cereals, have been identified in Hungary to date: 1966: barley yellow dwarf luteovirus (BYDV), 1984: barley stripe mosaic hordeivirus (BSMV), 1985: wheat streak mosaic tritimovirus (WSMV), 1986: brome mosaic bromovirus (BMV), cocksfoot mottle sobemovirus (CfMV), 1988: wheat dwarf mastrevirus (WDV), 1989: barley yellow mosaic bymovirus (BYMV), 1990: agropyron mosaic rymovirus (AgMV) and ryegrass mosaic rymovirus (RyMV). The most frequent and widespread of these are BYDV and WDV, which are thus able to cause the greatest quantitative and qualitative damage. On the basis of six years’ data (1994–2000), neither BYDV nor WDV could be isolated from 35.7% of 1163 samples exhibiting leaf yellowing and dwarfness. This indicates that other viruses pathogenic to cereals can induce similar symptoms. Among the plants showing symptoms of virus infection, 47.3% were attacked by WDV alone, in proportions ranging from 28.8% in barley to 69.7% in triticale. The degree of infection changed from year to year: WDV was isolated from 0.0% of symptom-exhibiting plants in 1999, from 48.5% in 1997 and from 94.0% in 2000. Barley yellow dwarf virus was only isolated alone from 9.5% of the samples, while it was isolated together with wheat dwarf virus from 7.5% of the samples. Considerable differences were observed between the cereal species: only 5.6% of the durum wheat samples were infected with BYDV, while this figure was 28.1% for oats. There was also a significant year effect. In 1996 triticale was not infected, while in 2000 5.0% of the plants exhibited symptoms and in 1994 45.5% of the plants were hosts to the BYD virus. Under Hungarian conditions all five known serotypes can be found, though in different proportions depending on the cereal species and the year. The most frequent is RPV (27.4%), followed by PAV (26.9%), SGV (15.6%), MAV (15.3%) and RMV (14.8%). In samples collected from oats only the PAV serotype was found. The MAV serotype has never been isolated from triticale. The dominant serotype was RPV (60.7%) in wheat samples, SGV (36.0%) in durum wheat and RMV (29.1%) in barley.

Field reaction of cassava genotypes to anthracnose, bacterial blight, cassava mosaic disease and their effects on yield

Barley yellow dwarf luteovirus (BYDV) serotypes PAV and RPV were identified from irrigated wheat (Triticum aestivum L.) samples from three provinces of Zambia by double antibody sandwich enzyme-linked immunosorbent assay using polyclonal and monoclonal antisera. Nine wheat cultivars were surveyed in 11 wheat fields. The virus caused stunting of the infected plants and leaf yellowing. The BYDV-PAV and BYDV-RPV serotypes were identified from 9 and 10 of the 11 surveyed fields, respectively, with the two serotypes co-infecting some plants. Of the nine wheat cultivars surveyed, four were infected with PAV, one with RPV and four with both serotypes. Disease incidence caused by BYDV in the surveyed fields ranged from 5 to 25%. This is the first report on the occurrence of BYDV in wheat in Zambia. Key Words: Barley yellow dwarf Luteovirus, detection, serology, serotypes, symptoms (African Crop Science Journal: 2000 8(2): 179-186)

Two barley yellow dwarf luteovirus serotypes associated with stunting of irrigated wheat in Zambia

Barley yellow dwarf luteovirus (BYDV) serotypes PAV and RPV were identified from irrigated wheat (Triticum aestivum L.) samples from three provinces of Zambia by double antibody sandwich enzyme-linked immunosorbent assay using polyclonal and monoclonal antisera. Nine wheat cultivars were surveyed in 11 wheat fields. The virus caused stunting of the infected plants and leaf yellowing. The BYDV-PAV and BYDV-RPV serotypes were identified from 9 and 10 of the 11 surveyed fields, respectively, with the two serotypes co-infecting some plants. Of the nine wheat cultivars surveyed, four were infected with PAV, one with RPV and four with both serotypes. Disease incidence caused by BYDV in the surveyed fields ranged from 5 to 25%. This is the first report on the occurrence of BYDV in wheat in Zambia. Key Words: Barley yellow dwarf Luteovirus, detection, serology, serotypes, symptoms (African Crop Science Journal: 2000, 8(2): 187-194)

Transmission, Characterization, and Serology of a Luteovirus Associated with Yellow Leaf Syndrome of Sugarcane

ABSTRACT A previously uncharacterized luteovirus was associated with one form of yellow leaf syndrome (YLS), a widespread disease of sugarcane (Saccharum sp.). The virus was named Sugarcane yellow leaf luteovirus (ScYLV), and was identified in major sugarcane-producing areas of the world. Typical disease symptoms were reproduced when ScYLV was transmitted by Melanaphis sacchari or Rhopalosiphum maidis from infected to healthy sugarcane, suggesting that this virus may be the causal agent of one form of YLS. The only known hosts of ScYLV are Saccharum and Erianthus spp. Virions of ScYLV were 24 to 29 nm in diameter in sodium phosphotungstate at pH 5.0, had a buoyant density of 1.30 g/cm(3) in Cs(2)SO(4), and contained a 5.8-kb genomic ssRNA. The capsid protein had an estimated relative molecular mass of 27 kDa and was not glycosylated. A polyclonal rabbit antiserum raised against ScYLV did not detect any of eight other luteoviruses by enzyme-linked immunosorbent assay or immunosorbent electron microscopy, but in immunoblot assays, antibodies to ScYLV detected the RPV serotype of Barley yellow dwarf luteovirus. It is concluded that ScYLV is a previously undescribed luteovirus that is biologically and serologically distinct from other members of the group and may be the causal agent of one form of YLS of sugarcane.

Barley Yellow Dwarf Virus RNA Requires a Cap-Independent Translation Sequence because It Lacks a 5′ Cap

A 3′ translation enhancer (3′TE) sequence that facilitates cap-independent translation is located near the 3′ end of barley yellow dwarf luteovirus RNA. Here, we show that the 3′TE is required for translation of the viral genome and thus for viral replication. Antisense inhibition showed that the 3′TE has significant secondary structure and is required for translation of virion RNA from infected plants and uncapped genomic transcripts but not for translation of capped transcripts. Direct end-labeling of RNAs verified the absence of a 5′ modification on virion RNA. Thus barley yellow dwarf virus differs from related viruses by having neither a genome-linked protein nor a 5′ cap.

Barley Yellow Dwarf Luteoviruses and Their Predominant Aphid Vectors in Winter Wheat Grown in South Carolina.

Barley yellow dwarf is recognized as an important disease problem in winter wheat production in the southeastern United States, but there is relatively little known about the ecology and epidemiology of barley yellow dwarf virus (BYDV) in this region. From 1991 to 1993, and in 1996 and 1997, winter wheat was sampled for BYDV throughout the principal wheat production areas in South Carolina. In addition, in 1997, a small number of samples were collected from fields in North Carolina and Kentucky. Plant samples were assayed to determine the BYDV serotype and, subsequently, coat protein sequences of isolates within the same serotype were compared using restriction fragment length polymorphisms. Representative BYDV isolates from South Carolina and type isolates from New York were compared in aphid transmission experiments using aphid species collected from South Carolina and laboratory colonies maintained in New York. The predominant BYDV serotype in South Carolina (in all years) was PAV, accounting for 94% of the total BYDV-infected samples analyzed. The RPV serotypes were more abundant in samples collected from western North Carolina and Kentucky. PAV isolates from all regions were identical to the New York BYDV-PAV in terms of serology and restriction fragment patterns. Furthermore, the aphid transmission phenotypes were similar for South Carolina and New York BYDV isolates. The predominant aphids colonizing winter wheat in South Carolina included Schizaphis graminum, Rhopalosiphum rufiabdominalis, R. padi, and Sitobion avenea. The South Carolina clones of R. padi and S. avenae were similar to the New York laboratory clones in their abilities to transmit various BYDV isolates from New York and South Carolina. In contrast to the New York clone of Schizaphis graminum that can vector SGV, PAV, and RPV, the S. graminum clone from South Carolina was not a vector of any BYDV serotype tested. R. rufiabdominalis was found to be an efficient vector of PAV, RPV, and RMV isolates, but did not transmit MAV or SGV.

Development of YLM, a codominant PCR marker closely linked to the Yd2 gene for resistance to barley yellow dwarf disease

The Yd2 gene in barley provides protection against barley yellow dwarf luteovirus (BYDV), the most economically devastating virus of cereals worldwide. Because resistance assays to identify Yd2-containing individuals from breeding populations are often difficult, we have developed a closely linked, codominant PCR-based marker for Yd2 using AFLP marker technology. The marker, designated YLM, can be amplified from barley genomic DNA prepared using a rapid and simple extraction procedure and, in a survey of more than 100 barley genotypes, was found to be polymorphic between most Yd2 and non-Yd2 lines. The YLM therefore shows excellent potential as a tool for selecting Yd2-carrying segregants in barley breeding programmes.

Plant virus and parasitoid interactions in a shared insect vector/host

AbstractInteractions between barley yellow dwarf luteovirus (BYDV) and the aphid parasitoid, Aphidius ervi Haliday (Hymenoptera: Aphidiidae), were investigated while sharing the vector/host, Sitobion avenae (F.) (Homoptera: Aphididae). Aphids, which were parasitized during their second larval stadium, had access to virus‐infected plants before, immediately after, or several days after parasitoid attack. The larval development of A. ervi in S. avenae was significantly delayed when virus acquisition took place before or shortly after the parasitoid had hatched, but not when the parasitoid was at the second larval stage during virus acquisition. Similarly, the presence of BYDV led to a significantly higher aphid mortality when they acquired virus up to and including the time that A. ervi was at the first larval stage. Adult female parasitoids deposited fewer eggs in viruliferous aphids. Virus transmission was not reduced by parasitization, and in some experiments aphids which were subjected to parasitoid attack transmitted BYDV more efficiently than unattacked insects.

Viruses and their significance in agricultural and horticultural crops in Finland

This paper reviews the plant viruses and virus vectors that have been detected in agricultural and horticultural crop plants and some weeds in Finland. The historical and current importance of virus diseases and the methods used for controlling them in cereals, potato, berry plants, fruit trees, ornamental plants and vegetables are discussed. Plant viruses have been intensely studied in Finland over 40 years. Up to date, 44 plant virus species have been detected, and many tentatively identified viruses are also reported. Control of many virus diseases has been significantly improved. This has been achieved mainly through changes in cropping systems, production of healthy seed potatoes and healthy stocks of berry plants, fruit trees and ornamental plants in the institutes set up for such production, and improved hygiene. At the present, barley yellow dwarf luteovirus, potato Y potyvirus and potato mop-top furovirus are considred to be economically the most harmful plant viruses in Finland.

Vectoring ability of aphid clones of Rhopalosiphum padi (L.) and Sitobion avenae (Fabr.) and their capacity to retain barley yellow dwarf virus

SummaryVectoring ability of four aphid clones, Rp‐M and Rp‐R26 of Rhopalosiphum padi and Sa‐R1 and Sa‐V of Sitobion avenae, to transmit barley yellow dwarf (PAV, MAV and RPV) luteoviruses (BYDV) was compared in controlled conditions. Significant differences between highly efficient vectors (HEV), Rp‐M and Sa‐Rl, and poorly efficient vectors (PEV), Rp‐R26 and Sa‐V, were found in transmission of their specific viruses with acquisition and inoculation access periods (AAP, IAP) of 5 days. BYD‐RPV was occasionally transmitted by both clones of S. avenae. None of 150 tested apterous adults of the Rp‐R26 transmitted BYD‐MAV, while 10% of transmission was observed from those of the Rp‐M in a parallel test. An improved ELISA and immuno‐PCR were adapted to test for viruses in aphids. The results obtained by the improved ELISA indicated there was a good correlation between virus detection in single aphids of HEV clones after a 5 day AAP and virus transmission by them. In contrast, the percentages of virus‐carrying aphids of PEV clones were generally higher than those of their transmission rates. BYD‐MAV and BYD‐RPV were also detected by the improved ELISA in single aphids of their PEV clones, with the exception of BYD‐RPV in those of Sa‐V. However, after a 2‐day IAP, the improved ELISA in most cases failed to detect these viruses in single aphids of PEV clones.Detection by immuno‐PCR demonstrated that all three viruses could be acquired and retained by the aphids of both HEV and PEV clones. But, as visualised from electrophoretic bands, after the 2‐day IAP the amplified products from aphid extracts of PEV clones were reduced. The detection in a batch of nine aphids by the improved ELISA revealed that virus content in PEV clones decreased more rapidly than that in HEV clones during transmission. Thus, the difference in transmission efficiency of the aphid clones within species was not caused by an inability to acquire virus, but was determined by variation in vectoring ability between them. This was due to differences in ability to prevent the passage of virions from haemocoel to salivary duct and/or different capacities for the retention of BYDV.

Two distinct mechanisms regulate luteovirus transmission efficiency and specificity at the aphid salivary gland.

Barley yellow dwarf luteovirus (BYDV) particles are transmitted by aphids in a species-specific manner. Transmission to plants requires that the virus particles be transported across the basal lamina and plasmalemma of the accessory salivary gland (ASG). To characterize the role of the ASG basal lamina in regulating BYDV transmission, five aphid species were microinjected with purified New York isolates BYDV-PAV or -RPV. Both viruses associated specifically only with the ASG basal lamina. The ability of virions to penetrate the basal lamina was separate from the ability to penetrate the plasmalemma. When the salivary glands of vector, Sitobion avenae, or non-vector, Rhopalosiphum maidis, aphids were incubated in vitro with New York isolate BYDV-MAV, virions only attached to the ASG basal lamina of S. avenae. When anionic and cationic ferritin were microinjected into aphids, only cationic ferritin aggregated on the surface of the ASG basal lamina and at openings of plasmalemma invaginations into the cytoplasm, suggesting that these sites had a net negative charge. In vitro studies of anionic and cationic gold penetration of ASG basal laminae indicated a macromolecular size exclusion limit of approximately 20 nm that depended on charge. Anionic gold particles did not accumulate in the basal lamina as densely as the 25 nm BYDV particles, suggesting that the virus particles have a greater affinity for the ASG basal lamina. These results indicate that both the ASG basal lamina and plasmalemma contain specific components independently involved in the recognition and transmission of luteoviruses.

Diversity among the coat proteins of luteoviruses associated with chickpea stunt disease in India†

Summary.Chickpea stunt is an important virus disease of chickpea in the Indian subcontinent which is thought to be caused by infection with a luteovirus. Samples of diseased chickpea plants were collected from different chickpea growing regions of India and analysed with a panel of monoclonal antibodies to potato leafroll, beet western yellows and barley yellow dwarf (RPV strain) luteoviruses. The results suggested that more than one luteovirus was present in chickpea crops near ICRISAT Asia Center, Hyderabad. Aphid transmission tests resulted in the separation of two distinct isolates from these samples. One of them (isolate L) was more efficiently transmitted by Myzus persicae than the other (isolate IC). Nucleotide sequence analysis of DNA obtained by reverse transcription‐polymerase chain reaction (RT/PCR) amplification revealed that the amino acid sequence of the coat protein of isolate L was 94% identical to that of beet western yellows virus, whereas the coat protein sequence of isolate IC was 82% identical to that of isolate L and 80% identical or less to those of the coat protein of other luteoviruses. Using newly designed “universal luteovirus primers”, a minor sequence variant of isolate IC, which was 96% identical to it in part of the coat protein gene, was detected in the same location during the next season. Only isolate IC could be detected in samples from other locations by either serological or nucleotide sequence analysis.

New Punctuation for the Genetic Code: Luteovirus Gene Expression

The luteovirus genome consists of a single RNA from which genes are expressed via subgenomic mRNAs and a variety of noncanonical translation events. We propose mechanisms of subgenomic RNA synthesis that accommodate the frequent recombination that has occurred at the termini of genomic and subgenomic RNAs. Luteoviral genes are translated by cap-independent translation, leaky scanning, ribosomal frameshifting, and stop-codon readthrough. Using the PAV barley yellow dwarf luteovirus as a model, we find that most of these translation events are controlled by sequences located hundreds to thousands of bases downstream in the viral genome. These signals are unprecedented in nature. A model is proposed in which a 3′ translational enhancer regulates viral RNA translation throughout the infection cycle.

Control of aphids and barley yellow dwarf virus in spring-sown cereals

The effects of sowing date and the timing of insecticidal applications on the colonization of cereal crops by aphids and incidence of barley yellow dwarf luteovirus were investigated. For three years (1990–1992) spring barley was sown in mid-March and mid-April, and one to three sprays of pirimicarb were applied prior to stem elongation. In 1990, yield declined with increased virus incidence; spray treatments just prior to stem elongation were most effective in aphid control but the benefit was short-lived. In 1991 and 1992, aphid migrations were relatively late, virus incidence was low and the sprays had no significant effect on aphid or virus abundance. Yields from early-sown plots were significantly greater than from plots sown late in all 3 years. Results suggest that spray regimes aimed at controlling aphids carrying BYDV into spring-sown crops are of little benefit and should be discouraged. In cases where some form of control is needed, appropriate timing of insecticide sprays depends upon the timing of aphid migrations relative to crop development and the infectivity of aphids migrating in the spring.