Incidence Of Barley Yellow Dwarf Virus Research Articles

Survey of Barley yellow dwarf virus incidence in winter cereal crops, and assessment of wheat and barley resistance to the virus

A survey of Barley yellow dwarf virus (BYDV) incidence in cereal crops in the Czech Republic over 4 years showed, on average, 13.3% BYDV-positive, randomly tested wheat and barley samples. The cultivated wheat and barley cultivars had different levels of susceptibility to BYDV infection. Field trials were performed with different barley and wheat breeding lines and cultivars, and resistance traits were evaluated after artificial inculcation by the viruliferous aphid vector Rhopalosiphum padi L. with BYDV-PAV. Our results showed high variability of visual symptom score (VSS) and reduction in grain weight per spike (GWS-R) in trials within the tested lines and cultivars. The barley line (WBON 96-123) and cultivars (Wysor, Travira) that contained RYd2 differed significantly from other cultivars in VSS. Line WBON 96-123 and cvv. Wysor and Yatzi showed the lowest GWS-R. Wheat line PSR 3628 and cvv. Altigo, Elan, Sparta, Aladin and Hewit showed significant difference from other cultivars in VSS. PSR 3628, Sparta, and Elan showed the lowest GWS-R. Similar results were obtained from BYDV titre analysis by RT-qPCR corresponding to the VSS and GWS-R traits. A low virus titre corresponded to low VSS and GWS-R. Hence, our results suggest that laborious and time-consuming GWS-R analysis could be replaced in some cases by qPCR-based BYDV titre analysis and, together with VSS evaluation, could enhance the efficiency of resistance assessment.

A comparative study of the Barley yellow dwarf virus species PAV and PAS: distribution, accumulation and host resistance

This study investigated the distribution and characteristics of the Barley yellow dwarf virus (BYDV) species BYDV‐PAS, which was recently separated from BYDV‐PAV, the most commonly studied BYDV species. Throughout 3 years of experimental monitoring of BYDV incidence, PAS was the most frequently occurring species infecting cereals and grasses in the Czech Republic. Furthermore, Rhopalosiphum maidis and Metopolophium dirhodum were recorded as BYDV‐PAS vectors, even though M. dirhodum does not usually transmit BYDV‐PAV. In field experiments with barley and wheat, where virus accumulation, symptoms and effect on the yield were tested, BYDV‐PAV was more severe than PAS. Infection with the BYDV‐PAV isolate resulted in greater expression of symptoms and also in a greater reduction in plant height and grain weight per spike than BYDV‐PAS. In a sensitive cultivar of barley (Graciosa), the amount of viral RNA of BYDV‐PAV was also significantly higher than that of BYDV‐PAS. In a tolerant line (Wbon‐123), however, no such differences were found. In conclusion, although BYDV‐PAS seems to be dominant in the Czech Republic, BYDV‐PAV has the potential to cause more significant crop losses in barley and wheat.

Biological and Serological Identification of Barley Yellow Dwarf Virus (BYDV) and Its Distribution in Iraq

Barley yellow dwarf virus (BYDV) was identified by means of symptoms on indicator plants, transmission by aphids, and serological characteristics. Symptoms of yellowing and stunting were appeared on leaf tips of Hordium vulgare, Triticum aestivum, and Avena fatua accompanied by stem stunting. Four species of aphids, Rhopalosiphum maidis, R. padi, Macrosiphum avenae, and Schizaphis graminum were found vectoring the virus. Extracts from wheat and barley plants showing yellowing and stunting were reacted positively with polyclonal anti-BYDV antiserum in DAS-ELISA. Most of samples that gave positive reactions by ELISA gave positive reactions with tissue blot immunoassay (TBIA). Higher incidence of BYDV was found in the northern parts of Iraq. Several economical and weed plants, collected from wheat and barley fields and vicinity sites have been found to harbor the virus. These hosts may acts as virus reservoir transmitting to wheat and barley plants by aphids.

A comparison of the occurrence of aphids and barley yellow dwarf virus in minimum-till and conventional-till autumn-sown cereals

SUMMARYWinter barley was sown by conventional-tillage (CT) and minimum-tillage (MT) cultivation over three seasons. Each cultivation treatment was split so that straw was incorporated into the soil during cultivation in one split, while the other did not receive straw. Aphid occurrences in autumn and incidence of barley yellow dwarf virus (BYDV) in spring were compared. Similar investigations on winter wheat were made over a further three seasons. The method of cultivation affected the number of aphids on barley and wheat plants in autumn and on wheat heads in summer; MT had fewest aphids. Soil incorporation of straw during cultivation had a similar effect. Method of cultivation affected the incidence of BYDV disease, with MT having least infection. Straw-treated cereal plots had fewer aphids and less BYDV than no-straw plots. Aphids and virus reached damaging levels only in the first barley crop. In this season, MT barley had significantly fewer aphids (48% fewer) and significantly less BYDV (71% less) than CT. Straw-treated plots within the CT system had rather similar aphid infestation and BYDV incidence as no-straw plots. Barley grown in the MT system with straw added had significantly fewer aphids (68%) than in the case when no straw was added. Overall, aphids in autumn were significantly fewer on MT relative to CT cereals in three of the six seasons and significantly fewer on straw relative to no-straw plots in two seasons. Aphids on wheat heads in summer were significantly fewer in MT relative to CT plots in one of the three seasons. Aphids on heads were also significantly fewer on straw-treated plots within each system of cultivation in two seasons, while MT wheat with straw had significantly fewer aphids/head than those without straw in one season. BYDV was lower each season in MT barley and wheat when compared with CT crops. These differences were significant for two of the three seasons in which each crop was grown. There was a lower incidence of virus in straw-treated plots than in no-straw plots. This effect was significant for one of the three seasons in which barley and wheat were grown. Plant and tiller density did not differ significantly between MT and CT barley either with or without straw incorporation. Plant density of wheat in autumn was significantly lower for straw-treated plots relative to no-straw plots in one season. Wheat head density was lower for MT relative to CT in one season, while MT with straw had significantly fewer heads than CT plots with straw in two seasons. BYDV significantly reduced grain yield only in 2001/02 when incidence of the disease was high. Grain yield in 2001/02 was 0·95 t/ha (16%) greater for MT barley, due to less BYDV, than for CT. Straw-treated CT barley outyielded no-straw plots by 0·45 t/ha, while the comparable value for the MT system was 0·3 t/ha. The combined effect of MT plus straw had a 1·24 t/ha (21%) yield advantage over CT without straw.It is concluded that MT cereals sown at the same time as CT crops in autumn have a lower risk of aphid infestation and BYDV infection than CT crops. The soil incorporation of straw further enhances the beneficial impact of MT in reducing aphids and virus.

First Report of Barley yellow dwarf virus-PAS in Wheat and Barley Grown in the Czech Republic.

Barley yellow dwarf disease, an important, ubiquitous virus disease of cereal crops worldwide, is caused by a group of related single-stranded RNA viruses assigned to luteovirus (Barley yellow dwarf virus (BYDV) spp. PAV, PAS, MAV, and GAV) or polerovirus (Cereal yellow dwarf virus-RPV) genera or unassigned to a genera (BYDV-SGV, BYDV-RMV, and BYDV-GPV) in the family Luteoviridae (2). Incidence of BYDV in cereal crops (e.g., barley, wheat, and oats) was high and reached epidemic levels in recent years in many regions of the Czech Republic. Previously, only PAV isolates have been identified here on the basis of serological detection (4), although antibodies to differentiate between PAV, PAS, and MAV are not widely available. Field samples of cereal crops were routinely tested in 2006 and 2007 and BYDVs were detected by ELISA. One-step-reverse transcription (RT)-PCR (Qiagen, Hilden, Germany) was adapted for BYDV detection using primer pairs BYcpF (5'-CCACTAGAGAGGTGGTGAATG-3') and BYcpR (5'-CCGGTGTTGAGGAGTCTACC-3') designed from conserved sequences identified by aligning multiple BYDV sequences available in public databases. These primers amplify a 641-bp fragment spanning nucleotides 2839-3479 from PAV (GenBank Accession No. EF043235) or PAS (GenBank Accession No. NC_002160) that includes a region of the coat protein gene and the intergenic region. RT-PCR amplicons were generated from two field isolates, PS-RuJK (spring wheat isolate, cv. Granny, collected in July 2007 from experimental plots at the CRI in Prague) and JE-120JK (winter barley isolate, cv. Merlot, collected in January 2008 from a barley field in Rychnov), both of which induced severe BYD symptoms. Amplicons were sequenced in both directions in a CEQ2000XL sequencer (Beckman Coulter, Fullerton, CA). The partial coat protein gene sequence of 483 nt of PS-RuJK and JE-120JK was analyzed and compared with available sequences of 26 PAV, 17 PAS, and 13 MAV isolates by MEGA4 (3). PS-RuJK (GenBank Accession No. EU863652) nucleotide and amino acid sequence identities ranged from 96.3 to 99.2% and 93.7 to 98.7%, respectively, for available PAS isolates, and 89.9 to 90.5% and 85.5 to 86.9%, respectively, for available PAV isolates, and 78.3 to 79.5% and 70.0 to 72.5%, respectively, for available MAV isolates. Similarly, nucleotide and amino acid sequence identities JE-120JK (GenBank Accession No. EU863653) ranged from 95.2 to 98.6% and 90.6 to 96.9%, respectively, for PAS isolates, 88.8 to 90.1% and 83.1 to 84.4%, respectively, for PAV isolates, and 77.6 to 78.7% and 67.5 to 70.0%, respectively, for MAV isolates. Also, both of these isolates have the conserved amino acid motif "SIPGS" that is usually present in a variable region of the coat protein gene on the surface of virion (1) at position 52 to 56 of amino acid sequences of all published PAS-like isolates, including Vd29:AY167109, FH1:AJ223588, MA9516:AJ007926, FL2:AJ223586, ASL-1:AJ810418, and WS6603:DQ285680, contrary to "PVFRP" or "LISGP" motif in PAV or MAV, respectively. Therefore, the sequence data clearly confirm that these two isolates belong to the PAS species. To our knowledge, this is the first record of PAS detected in the Czech Republic.

Quantification of Yield Losses Caused by Barley yellow dwarf virus in Wheat and Oats.

Grain yield data obtained from five field experiments in Western Australia from 1992 to 1994, in which insecticide applications suppressed the spread of Barley yellow dwarf virus (BYDV) in wheat and oats, were used to quantify the relationships between incidence of BYDV and yield gaps, 500-seed weight, and percent shriveled grain. Yield gaps ranged from 0 to 2,700 kg/ha, and the relationship between yield gap and incidence of BYDV was always linear. Single point yield loss models revealed that BYDV infection explained most of the variation in yield gaps. There was a significant linear relationship between incidence of BYDV and 500-seed weight for wheat, but not for oats. The percent shriveled grain always increased with an increase in incidence of BYDV in wheat but not in oats. Cost-benefit relationships were determined for the return on investment when deploying imidacloprid-treated seed and/or one or two foliar applications of pyrethroid insecticides to reduce incidence of BYDV and to decrease the yield gaps in wheat and oats due to BYDV.

Yield Effects of Barley yellow dwarf virus in Soft Red Winter Wheat

ABSTRACT Three cultivars of soft red winter wheat were evaluated to determine the relationship between the incidence and time of infection by Barley yellow dwarf virus (BYDV) and yield. Wheat was planted in 1995, 1996, and 1997 in a split-plot design with six replicates at sites in Indiana and Illinois. Yield plots were infested with different amounts of viruliferous aphids, and the incidence of BYDV in each plot was measured. In a 2-year study in Illinois with cv. Clark and the PAV-IL isolate of BYDV, yields were assessed following aphid infestation in fall, early spring, and late spring. Early spring infections resulted in larger yield reductions than late spring infections in both years and larger than fall infections in one year. Regression analyses to relate incidence of infection and yield with data from fall and early spring infections provided R(2) values of 0.89 and 0.51 for the 1996 to 1997 and 1997 to 1998 seasons, respectively. An additional study at the same site in the 1996 to 1997 season compared the yield responses of cvs. Clark, Y88-3e, and PT8935b. Increases in the incidence of BYDV correlated with decreases in yield, with R(2) values of 0.80, 0.78, and 0.90 for the three cultivars, respectively. Estimated yield losses in both studies and all cultivars ranged from 27 to 45 kg/ha or 0.34 to 0.55% for each percent increase in virus infection. In a third study over a 2-year period in Indiana with the same three wheat genot ypes and a second BYDV isolate (PAV-P), BYDV treatments resulted in significant reductions in yield, but yield loss and the incidence of BYDV were not linearly correlated. Given the differences in yield reductions caused by the two BYDV isolates, PAV-P may be an attenuated strain of BYDV and may cross-protect plants from naturally occurring strains of the virus.

Impact of cereal aphids on wheat yields in southern New South Wales, Australia

The effect of naturally occurring aphid infestations on yield was studied using sprayed and unsprayed plots in commercial wheat crops at a number of sites in southern New South Wales, Australia. In 1990, wheat was planted in April or early May following early autumn rains. Aphids were first found in the crops 4 weeks after the wheat was sown. Numbers were generally low and only at 1 site was there a significant effect on yield. In 1991, sowing was delayed by prolonged dry weather during autumn. Most crops were planted in late May and aphids started to appear only in mid July. There was no significant effect of aphids on yield but most crops were badly affected by drought. In 1991, labelled plants at some sites were used to study the impact of varying levels of aphid infestation on yield. There was a significant negative correlation between the number of aphids and yield per plant at 1 site. In both years, aphid numbers peaked in August or September. Rhopalosiphum padi was virtually the only aphid species found. Leaf samples were collected from 3 sites in 1990 and from all sites in 1991 and tested for barley yellow dwarf virus. The incidence of this virus was very high in 1990 but negligible in 1991. The striking difference in the incidence of barley yellow dwarf virus in the 2 years was most likely the result of later sowing times and delayed arrival of aphids in crops in 1991. Aphids may have a considerable impact on yield in early-sown wheat through transmission of barley yellow dwarf virus.

The incidence of strains of barley yellow dwarf virus in perennial ryegrass crops in south‐west and central Scotland

The incidence of barley yellow dwarf virus (BYDV) in perennial ryegrass (Lolium perenne) crops in four areas of south‐west and central Scotland was investigated between March 1988 and February 1989. BYDV was detected in 93·8% of the grass swards using an indirect enzyme‐linked immunosorbent assay (ELISA). This enabled the seasonal periodicity of the BYDV strains to be monitored over 12 months for the first time in Scotland. The incidence of the RPV, PAV and MAV strains of BYDV declined between March and July 1988, before gradually rising in August. Incidence increased markedly in September, especially of the RPV and MAV strains, and then gradually decreased over the winter months, before stabilizing in February 1989. The incidence of the different strains in perennial ryegrass leys varied between geographical areas and between fields within areas. Most ryegrass samples contained a mixture of the three strains of BYDV. RPV was the most common strain in Ayrshire, while the incidence of PAV was highest in Wigtownshire and that of MAV was highest in Dumfriesshire and Stirlingshire. The incidence of BYDV increased with the age of the sward. The role of perennial ryegrass as a source of virus for the infection of cereals is discussed.

Effects of barley yellow dwarf virus on the yield of winter wheat

Yield responses were measured of six winter wheats to field infections with Barley Yellow Dwarf Virus (BYDV). In addition to the natural incidence of virus, the range of infection levels was widened by aphicide spraying of some plots and the addition of artificially propagated viruliferous aphids to others. Significant grain yield losses attributable to natural infections by BYDV were found for all wheats despite the main infection period being in the spring. The addition of viruliferous aphids only marginally decreased yields further. Spraying with aphicides did not exclude infection but did reduce the incidence of BYDV and increase yields. A significant negative linear correlation between grain yield and percentage infection applied to each wheat genotype. The slope of the yield response appears to be a more useful measurement for comparing tolerance to BYDV of differing cereal lines than do proportional yield losses. Of the six wheats tested, Lawson, Birch 41, Birch 75, Owlet and Isis had similar tolerances to BYDV, despite substantial differences in absolute yields, while W71 was considerably more vulnerable. The mean natural incidence of BYDV in the main trial was 67%, producing an expected grain yield loss of about 2.2 t ha-1 for W71 and about 1.1 t ha-1 for the other five wheats. Effects on grain protein and potential control measures are also discussed.

Seasonal Occurrence of Barley Yellow Dwarf Virus Serotypes in Small-Grain Cereals in the Valley of Mexico

We assessed the occurrence of serotypes of barley yellow dwarf virus (BYDV) in an area at the International Maize and Wheat Improvement Center (CIMMYT) used to screen germ plasm for field resistance to BYDV. Wheat and barley plants were labeled in the field, and leaves were sampled several times during plant development to monitor BYDV incidence. Samples were tested by enzyme-linked immunosorbent assay with a panel of monoclonal and polyclonal antibodies. Samples from plantings sowed on different dates were tested to investigate seasonal influences on BYDV occurrence. Up to 88% of the plants sowed in winter (November and January) became infected. Fewer infections were detected in summer sowings (May) (.)

Occurrence of barley yellow dwarf virus in cereals and grasses of the low‐rainfall wheatbelt of South Australia

South Australia is in the dry temperate zone where most cereal crops are grown in an area of low rainfall, with a crop‐free season from December to April. The incidence of barley yellow dwarf virus (BYDV) was assessed by ELISA from 1989 to 1991 in wheat crops and irrigated pastures of South Australia. The incidence of BYDV was low in most wheat crops of the low‐rainfall area in 1989 and 1990 (less than 1% of plants infected), but moderate levels of infection (1–10%) were observed in some early‐sown crops. BYDV infection was more widespread in the high‐rainfall area (south east of South Australia). A high incidence of BYDV was observed in the irrigated pastures of the three areas surveyed (4–86%). Of the five previously described strains, the Rhopalosiphum padi/Sitobion avenae strain (PAV) was the most common in wheat samples (> 90%). PAV and the R. padi‐specific strain (RPV) were found in pasture grasses, alone or in mixed infection. Virus incidence was greater in Festuca spp. (56%) and Lolium perenne (30%) than in other species (2‐–9%).

A Simulation Model of the Epidemiology of Barley Yellow Dwarf Virus in Winter Sown Cereals and its Application to Forecasting

1. A computer model is described which simulates the spread of barley yellow dwarf virus (BYDV) by aphids in winter cereals in SW England. The model has as a theoretical base the dynamic interaction between two temperature-dependent rate processes: (i) the frequency of virus transmission to uninfected plants by infected aphids, and (ii) the frequency of virus acquisition by uninfected aphids from infected plants. A distinction is made between virus spread into crops by alate migrant vectors (primary transmission), and more localized spread within crops mainly by apterous vectors (secondary transmission). Both types of spread may occur concurrently. Probabilities of multiple infection, and effects of this on the rate processes in the model, are described by a generalized frequency distribution. Vector dispersal and the latent periods, following transmission and acquisition of virus, are represented as constant functions of thermal time. 2. Simulations used field data of plant and aphid populations sampled every few weeks in crops of winter barley and wheat at Long Ashton near Bristol during 1978-89. The infectivity of autumn migrant aphids caught each year in a suction trap was measured by feeding transmission tests. Daily max-min screen temperatures used to estimate thermal time were obtained from records at Long Ashton. Crop infections were assessed from visible symptoms or by enzyme-linked immunosorbent assay (ELISA). 3. The model was successfully validated for 61 cereal crops with 0-80% of the crop area affected. There was no significant divergence between field observations and incidence of BYDV as predicted by the model (barley, r = 0-98; wheat, r = 0.94). Curves of epidemic development obtained by measuring virus incidence at frequent intervals during crop growth were usually similar to those generated by the model. Prospects for practical and more reliable forecasting of BYDV epidemics, and of the need for control measures, are discussed.

Effects of straw disposal and tillage on spread of barley yellow dwarf virus in winter barley

SummaryThe effects of straw baling or incorporation, combined with ploughing, non‐inversion tillage, or direct drilling on the incidence of barley yellow dwarf virus (BYDV), were investigated in plots of winter barley. Virus infection was more prevalent after ploughing (> 40% of the plot area damaged) than after non‐inversion tillage (9 – 24%) or direct drilling (< 3%). For each cultivation method, more infection was associated with straw baling than with straw incorporation. There was a strong negative correlation between plot yields and the incidence of BYDV(r= ‐0.87).Monthly pitfall sampling of non‐specific aphid predators showed that the population activity of several taxa (e.g. Linyphiidae, and the larger species of adult and larval Carabidae and Staphylinidae) declined for a short period in autumn‐winter following cultivation. The overall treatment‐ranking for numbers of predators in autumn (direct drilled > non‐inversion > ploughed) was the opposite of subsequent virus infection. The possible roles of aphid predators and other biological mechanisms in determining the observed effects on BYDV, are briefly discussed.

Occurrence of barley yellow dwarf virus in pastures of western France

As pasture grasses are preponderant in the agriculture of western France, their role as reservoirs of barley yellow dwarf virus (BYDV) and its aphid vectors has been studied from 1984 to 1986. Aphids were observed on most crops of five pasture grass species (brome grass, cocksfoot, tall fescue, Italian and perennial ryegrass) but in very low numbers. Rhopalosiphum padi was the most numerous species. The incidence of BYDV was high, with levels of infection ranging from 6 to 80% depending on the species of pasture grasses. Fescue pastures were highly infected with BYDV, whereas the virus was not detected in cocksfoot pastures. PAV‐, RPV‐, MAV‐like isolates of BYDV were detected in pasture grasses, but RPV‐ and MAV‐like isolates were only detected from ryegrass and brome grass, respectively. The role of these grasses as source of viruliferous aphids infecting cereals is discussed.

The incidence of barley yellow dwarf viruses in wheat in Victoria

Wheat crops from all major wheat-growing districts throughout Victoria were sampled during September 1984. Examination of pooled samples by enzyme-linked immunosorbent assay (ELISA) with an antiserum to a mixture of two barley yellow dwarf virus (BYDV) types ('V1') showed that 10 out of 26 crops were infected with BYDV and 3 out of 26 had a BYDV incidence greater than 10%. The overall loss in yield likely to result from BYDV was estimated at 2% with a far greater loss in some crops. Frozen-stored samples from four crops with high levels of BYDV were retested after one year with isolate-specific antisera. The results indicated that in these crops, PAV-related isolates were the most common, followed by RPV-related isolates.

Effects of fungicides and insecticides applied to spring barley sown on different dates in 1976-79

SUMMARY Factorial experiments in 1976–1979 investigated the effects of sowing date, fungicides (ethirimol seed treatments and tridemorph sprays) and insecticides (phorate applied to the soil, and menazon or dimethoate sprays) on powdery mildew, aphids, barley yellow dwarf virus (BYDV) and grain yield of spring barley (cv. Julia in 1976 and 1977; cv. Wing in 1978 and 1979). Late sowing usually increased the severity of powdery mildew, numbers of aphids and incidence of BYDV and generally decreased yield. Responses to pesticides were commonly greater on the late-sown than on the early-sown barley. Response to fungicides are principally attributed to the control of powdery mildew (Erysiphe graminis f. sp. hordei; the target species) but responses to insecticides cannot be attributed to virus control and seem unlikely to be due solely to control of aphids, whose numbers were relatively small. There were some effects of fungicides on aphids and insecticides on mildew, but they were inconsistent and too small to affect crop protection strategies.

Incidence of barley yellow dwarf virus in ryegrass pastures in New Zealand

Abstract The percentage of plants infected with barley yellow dwarf virus (BYDV) was determined in each of 45 New Zealand ryegrass pastures during the summer of 1975–1976. Incidence of BYDV infection was extremely variable in pastures of similar age, but 1- to 2-year-old pastures generally had fewer infected tillers than did older swards. Many 6- to 30-year-old pastures had over 50% of plants infected with BYDV. Highest virus infection was 84% in two perennial ryegrass pastures aged 8 and 15 years. Pastures at Palmerston North had a slightly higher incidence of BYDV than those at Kaikohe and Lincoln. Pastures in the far south of the South Island appeared to have a low incidence.

Barley yellow dwarf virus in aphids caught in suction traps, 1969-73.

SUMMARYSuction traps operating at low level (1 5 m) were used to catch live alate Rhopalosiphum padi, Macrosiphum (Sitobion) avenae and Metopolophium dirhodum which were tested for transmission of barley yellow dwarf virus (BYDV). The first species caught and infective was R. padi, followed by M. (S.) avenae infective some 2–3 wk later and M. dirhodum 3–4 wk later still. Never more than 11‐5% of the annual catch of any species transmitted BYDV and the proportion fluctuated from week to week and between seasons in different years.The relative abundance of infective vectors of ths three species varied; annual numbers of infective M. (S.) avenae and M. dirhodum varied inversely with infective R. padi, the latter also usually transmitted severer virus. The results of the infectivity tests have been compared with the catches of these aphids by the Rothamsted Insect Survey and show that numbers of alate aphids do not necessarily indicate the likely incidence of BYDV.

Control of Aphids Attacking Barley and Analysis of Yield Increases in the Imperial Valley, California1

A study was conducted from 1958 to 1963 in the Imperial Valley, California. to determine whether the incidence of barley yellow-dwarf virus can be controlled with pesticides and whether direct feeding by the oat bird-cherry aphid, Rhopalosiphum padi (L.), and the corn leaf aphid, R. maidis (Fitch), caused sufficient barley injury to warrant the expense of insecticide treatment. Only an occasional barley plant that had virus disease symptoms was found, thus it was not possible to determine whether aphid control with pesticides could control the spread of the virus. Analysis of yield data indicates that in areas where barley yellow-dwarf virus is not a problem, or in years when the incidence of the disease is very low, yield increases above the cost of treatment may be expected when aphids are controlled at a level that is expected to average about 25-30 aphids per tiller. When aphids markedly rise above this level very substantial yields may be expected when aphids are controlled. Phorate (44D) seed-coat treatments were found to be unsatisfactory because of reduced seed germination and short-term control. Ten percent phorate granules at 7.5-10 lb/acre applied by airplane, followed by irrigation, gave excellent to very good aphid control.