Soybean Rust Incidence and the Response of Soybeans to Fungicides in 7 Dr. Patrick M. Phipps, Professor of Plant Pathology Virginia Tech, Tidewater AREC, 6 Holland Rd., Suffolk, VA 47 (Email: pmphipps@vt.edu; Telephone: 757-657-645, Ext. 4) Dr. Erik L. Stromberg, Professor of Plant Pathology Virginia Tech, Dept. Plant Pathology, Physiology & Weed Science, Blacksburg, VA 46 (Email: elstrom@vt.edu; Phone: 54--66) Dr. Steve Rideout, Assistant Professor of Plant Pathology Virginia Tech, Eastern Shore AREC, 446 Research Drive, Painter, VA 4 (Email: srideout@vt.edu; Phone: 757-44-74) Dr. David Holshouser, Associate Professor of Crop, Soil and Environmental Sciences Virginia Tech, Tidewater AREC, 6 Holland Rd., Suffolk, VA 47 (Email: dholshou@vt.edu; Telephone: 757-657-645, Ext. 4) Mr. Robert Pitman, Superintendent Virginia Tech, Eastern Virginia AREC, 9 Menokin Rd., Warsaw, VA 57 (Email: rpitman@vt.edu; Telephone: 84-45-965) Acknowledgements: This research was supported by the Virginia Agricultural Experiment Station, the Virginia Soybean Board, and the Virginia Department of Agriculture and Consumer Services. The authors thank Steve Byrum, Barron Keeling, Ed Hobbs, Christine Waldenmaier, Elizabeth Bush, and Mary Ann Hansen for assistance in diagnostic laboratories, field trials and data processing. 7 GROWING SEASON Rainfall in May, June, July, August and September was.66,., 4.6,.7 and 4.9 in. below normal, respectively, and October was.74 in. above normal at the Tidewater AREC in Suffolk. Rainfall during the period totaled 7.56 in. which was. in. below normal. Minimum air temperatures averaged near normal (± F) in June, July and September, F above normal in August, F above normal in May, and 9 F above normal in October. Maximum air temperatures were near normal (± F) in May and July, F above normal in June and September, 5 F above normal in August, and F above normal in October. Most fields planted to full-season soybeans showed good emergence after planting, whereas drought stress in some areas planted to double-cropped soybeans after wheat harvest showed delayed emergence. SOYBEAN RUST IN 7 The initial findings of the fungus on soybeans were generally within miles of kudzu vines which provided green leaves for growth and sporulation of the fungus during winter months and after soybeans were planted. The spread of soybean rust northward through states 8 Virginia Polytechnic Institute and State University 8-6 Virginia Cooperative Extension programs and employment are open to all, regardless of race, color, national origin, sex, religion, age, disability, political beliefs, sexual orientation, or marital or family status. An equal opportunity/affirmative action employer. Issued in furtherance of Cooperative Extension work, Virginia Polytechnic Institute and State University, Virginia State University, and the U.S. Department of Agriculture cooperating. Mark A. McCann, Director, Virginia Cooperative Extension, Virginia Tech, Blacksburg; Alma C. Hobbs, Administrator, 89 Extension Program, Virginia State, Petersburg.
along the Atlantic Coast began on soybeans in Alabama, Georgia, Florida and Texas. By July 5, the disease had been reported on soybeans in eastern Texas, Louisiana, Mississippi, Alabama, Florida, and Georgia (Fig. A). Rainfall in eastern Texas and parts of Oklahoma, Louisiana, Arkansas, Mississippi and Alabama favored disease spread into the Mississippi Valley whereas widespread drought throughout the Mid-Atlantic Region suppressed spread of soybean rust in September, October, and November in 7 (Fig. B, C). The disease was first detected in South Carolina on August, North Carolina on 4 September, and Virginia on 9 October. A B Jul 5 C Sept 5 Nov 5 Fig.. Counties with soybean rust on 5 July, 5 September, and 5 November 7 The distribution of counties with soybean rust through 5 November 7 matched well with the expected pattern of disease spread from south to north and the distribution map for planted acres of soybean in the United States (Fig. ). It seems likely that the delayed spread of disease until after September was likely a result of the low concentration of soybean acreage in coastal areas bordering the Gulf of Mexico and disease suppression by drought stress in the southeast and states in the Mid-Atlantic Region. Fig.. Distribution of planted acres of soybean by counties across the U.S. in 6.
DISEASE INCIDENCE AND YIELD LOSSES IN 7 Soybean yields in 7 were estimated to average 7 bu/a on an estimated 48, acres harvested in Virginia. Nematodes had the greatest impact on yield based on diagnostic tests performed in the plant disease clinic at the Tidewater AREC and field observations in Eastern Virginia (Table ). Leaf diseases (frogeye leaf spot, anthracnose, Cercospora blight) in 7 showed low incidence which is expected in years of excessive dry weather stress. Low yields were likely a result of dry weather stress and root damage by nematodes (Table ). Soybean cyst, southern and northern root-knot, sting, lance and stubby root nematodes probably accounted for the greatest losses of yield. Soybean rust was first detected on 9 October through weekly examinations of leaf samples from sentinel plots and numerous commercial fields. Further sampling up to November confirmed incidence of the disease in a total of nine counties; all located in southeastern Virginia. Soybean rust was believed to cause no significant loss of yield in Virginia due to low incidence and late appearance. Essentially all soybean fields were beyond R6 (full seed stage) when the disease was detected. Table. Estimated loss in yield as a result of soybean diseases in 7. Disease Causal agent(s) Percent loss Seedling diseases... Rhizoctonia spp., Pythium spp., etc.....5 Cercospora blight... Cercospora kikuchii. Purple seed stain... Cercospora kikuchii. Downy mildew... Peronospora manshurica Trace Anthracnose... Colletotrichum truncatum.4 Brown spot... Septoria glycines. Pod & stem blight... Diaporthe phaseolorum var. sojae. Frogeye leaf spot... Cercospora sojina Asian soybean rust... Phakopsora pachyrhizi Southern blight... Sclerotium rolfsii. Brown stem rot... Phialophora gregata. Charcoal rot... Macrophomina phaseolina. Stem canker... Diaporthe phaseolorum var. caulivora Trace Sudden death syndrome... Fusarium solani f.sp. glycines Trace Root & lower stem rot... Rhizoctonia spp. Trace Red crown rot... Cylindrocladium parasiticum Trace Phytophthora root & stem rot... Phytophthora megasperma f.sp. glycinea Sclerotinia stem rot... Sclerotinia sclerotiorum and S. minor Viruses... SMV, PMV, BPMV, etc. Trace Bacterial pustule... Xanthomonas phaseoli Trace Bacterial blight... Pseudomonas glycinea. Soybean cyst nematode... Heterodera glycines. Southern root knot nematode... Meloidogyne incognita.5 Other nematodes... ---various---.5 Total loss (%)... 6.* * The loss estimate equals 87,76 bushels based on production of.96 million bushels in 7. At a value of $.5/bu, the loss in revenues at the farm gate would be 9.5 million dollars.
SENTINEL PLOTS Ten regional sentinel plots were sampled from flowering up to beginning senescence for early detection of soybean rust in 7 (Table ). A total of 64 samples of leaflets were processed from sentinel plots by microscopic examination; 7 at the Tidewater AREC, 54 at the Eastern Shore AREC, and 8 at the PPWS Department in Blacksburg. Sentinel plots were located at the Tidewater AREC in Suffolk, Charles City County, Mecklenburg County, Greensville County at Skippers, Eastern Shore AREC at Painter, Northampton County, Shenandoah County, Northern Piedmont AREC at Orange, Eastern Virginia AREC at Warsaw, and Virginia Tech Kentland Farm at Blacksburg. Leaf samples were collected and either shipped overnight by site cooperators or hand carried to the Tidewater AREC, Eastern Shore AREC, or the Virginia Tech - PPWS Department for processing. A total of 66 samples from 84 commercial fields in 6 counties were processed in 7 (Table ). The Tidewater AREC processed 87 samples and the Eastern Shore AREC processed 79 samples. Upon receipt, the samples were placed in moist chambers at room temperature (7º - 77 F), incubated for to 5 days, and examined under a dissecting microscope for pustules of soybean rust. Microscopic examinations of samples from sentinel plots and commercial fields resulted in detection of soybean rust on leaflets from a commercial field in Isle of Wight County on 9 October. Continued sampling up to 5 November confirmed incidence of the disease in a total of 9 counties (Chesapeake, Gloucester, Isle of Wight, Matthews, Middlesex, Suffolk, Surry, Sussex, and Virginia Beach). Photographs of leaflets were taken to illustrate the small size of lesions and the need for microscopes to find and identify rust pustules (uredinia) and spores for disease detection (Fig ). Confirmation of positive samples with pustules on leaflets was obtained by ELISA tests on of samples in the laboratory. Table. Sentinel plot samples processed for soybean rust in 7. June July August September October November Total Total County -* + - + - + - + - + - + + samples Accomack... 5 8 7 Charles City... 6 5 7 9 Greensville... 8 5 6 Mecklenburg... 7 4 8 Montgomery... 4 9 5 Northampton... 8 9 8 7 Orange... 5 9 6 Richmond... 8 9 Shenandoah... 6 Suffolk... 7 8 Total... 7 55 7 6 64 * - equals number of samples negative for soybean rust; + equals number positive. 4
Table. Commercial field samples processed for soybean rust in 7. County June July Accomack... Brunswick... Chesapeake... Dinwiddie... Essex... Gloucester... Greensville... Isle Of Wight... James City... King & Queen... King William... Lancaster... Matthews... Mecklenburg... Middlesex... New Kent... Northampton... Northumberland.. Nottoway... Prince George... Southampton... Suffolk... Surry... Sussex... Virginia Beach... Westmoreland... -* + 5 5 + Total... 5 August + 8 8 5 September + 8 8 October + 5 November + 5 5 4 6 Total Total + Samples 4 8 4 4 4 4 4 6 6 66 * - equals number of samples negative for soybean rust; + equals number positive. A C D B Fig.. A) Soybean rust pustules circled on leaflet; B) pustule under dissecting scope; C) pustule highly magnified under dissecting scope; and D) rust spores magnified under compound microscope. 5
WET AND AIR DEPOSITION SPORE TRAPS Five spore traps each for monitoring wet deposition and air deposition of spores were used from June through September for detection of rust spores moving into Virginia. Spore traps were located at the Tidewater AREC (Suffolk), Eastern Virginia AREC (Warsaw), Northern Piedmont AREC (Orange), Eastern Shore AREC (Painter) and Virginia Tech (Blacksburg). Samples were collected from the wet deposition spore traps (Fig. 4) on an 8 micron filter after significant rain events. These samples were sent to Dr. Erik Stromberg (Virginia Tech) for PCR analysis of filter contents. A total of only three filters from wet deposition spore traps were positive for spores of soybean rust. Greased slides were used in five dry deposition spore traps to Fig. 4. Wet deposition trap. sample air continuously for one week intervals. Each week a single greased slide was removed from the traps and sent to Dr. John Rupe at the University of Arkansas for examination. Spores of soybean rust were not found on any of the greased slides from dry deposition traps. These results were based on the absence of rust spores with morphological traits matching that of the Asian soybean rust fungus, Phakopsora pachyrhizi. The presence of soybean rust spores was responsible for detection of Phakopsora pachyrhizi in wet deposition traps by PCR tests. However, it is not known if the spores were capable of germination and causing infection. Table 4. Detection of Phakopsora pachyrhizi in wet deposition spore traps, 7. Number of Positive Trap dates of samples Trap location submitted results* positive results TAREC, Suffolk... Aug 7-4 NPAREC, Orange... 9 -ESAREC, Painter... -Virginia Tech, Blacksburg... 9 -EVAREC, Warsaw... Aug 6 - Aug 7-Sep Rain amount (in.). ---.8. *Results confirmed by PCR. SEASONAL AIR TEMPERATURES AND RAINFALL IN 7. Moderate to severe drought stress occurred across much of eastern Virginia in 7 and at locations of fungicide trials on soybeans. Periods of dry weather stress in July and September and above normal temperatures in July and August and September were believed to be responsible for reduced yields and the late appearance of soybean rust in South Carolina, North Carolina, and Virginia in 7. Unlike 6 when tropical storm Ernesto brought soaking rains at the end of August, no tropical storms brought rainfall into the Coastal Plain or Piedmont areas of Virginia in 7. Table 5 summarizes seasonal temperatures at locations where fungicide trials were conducted on soybean in 7. All locations reported below normal rainfall for the period from May through October. Weather data in Suffolk and Skippers were obtained from the Peanut/Cotton InfoNet (http://www.ipm.vt.edu/infonet). The Virginia Agricultural Experiment Station Mesonet (http://www.ahnrit.vt.edu/research/weather.html) collected weather data at the Eastern Virginia AREC at Warsaw and the Eastern Shore AREC at Painter. Normal rainfall records were obtained from annual reports by the Virginia Agricultural Statistics Service. 6
Table 5. Weather summary for locations of fungicide trials in 7. 7 Air Temperatures (F) Rainfall (in.) Location Month Avg. Max Min. 7 Normal Tidewater AREC, Suffolk Hawkins Farm, Skippers Eastern Shore AREC, Painter Eastern VA AREC, Warsaw MAY 65.4 76.5 54.9.6.8 JUN 74. 85.5 6.7. 4. JUL 76. 88. 65.9.7 5.87 AUG 77.4 89. 67.6 5. 5.7 SEP 7.7 8.9 58.5.4 4.5 OCT 66. 79. 54.8 5.6.5 Mean 7.7 8.7 6.9 Total 7.56 7.77 MAY 67. 78.6 55.7.6.85 JUN 75.8 87. 65..4.57 JUL 77.6 9. 66..6 4.96 AUG 8.5 94. 69.8.5 4.6 SEP 7.7 86. 6.6.69 4.5 OCT 66. 79.6 54.7 4.5.6 Mean 7. 86. 6. Total 5.86 4. MAY 6.4 7.4 5..9.8 JUN 7.7 8. 6.9 5..6 JUL 75.9 84.6 67..66 4.74 AUG 76.7 85.6 68..8 4. SEP 7. 8.4 6.9.49.64 OCT 67. 75.9 58..65.69 Mean 7. 8. 6.9 Total 7..8 MAY 65. 76.6 5.7.9 4.5 JUN 74. 84.5 6.5.4.6 JUL 76. 88. 65.8.88 4.6 AUG 77.7 88. 68..58 4.46 SEP 7.4 8.8 58.7.9 4.4 OCT 65.4 76.4 55..7.4 Mean 7.5 8.8 6.9 Total.5 4.9 The optimum temperature range for leaf infection and development of rust pustules is 68 to 77º F. In addition to favorable temperature, the fungus requires moisture (leaf wetness or > 95% RH) for spore germination and infection of leaflets. In an attempt to determine when conditions were favorable in 7, the number of days with daily average temperatures between 6 to 77º F and short-term rainfall totals were.5 in. in the previous 5 days, in. in the previous days, or periods of relative humidity were 95% for or more hours. According to data collected at the Tidewater AREC, favorable conditions for infection were recorded for 8 days in May, days in June, 8 days in July, 4 days in August, days in September, and days in October. The longest periods of favorable conditions for infection occurred for 6 of days beginning in July (Jul to Aug ) and 4 of 9 days in late September and early October (Sep to Oct 8). The latter period appears to be the most plausible for explaining the first detection of soybean rust on October 9 in Virginia. 7
FUNGICIDE TRIALS: Plots were -ft long and -ft wide. Row spacing ranged from 8- to -in. depending upon location. A randomized complete block design was used with four replications of treatments. Fungicides were applied with either a CO -pressurized backpack sprayer in a 6-ft spray swath, or a Lee Spider sprayer in a -ft spray swath. Both sprayers were equipped with 8VS or Tee Jet 5 nozzles spaced 8- in. apart and delivered a volume of 6.5 to gal/a at to 4 psi depending upon the location. Disease and yield data were collected from the central, 4.75-ft by -ft long section in each plot. Plots were harvested with a self-propelled, small-plot combine. Results Tidewater AREC, Suffolk, Trial 7 (Phipps). The field site was planted to RT 545N on 4 May. The soil type was Nansemond fine sandy loam that was planted to soybean from 4 through 6. Plots were eight, -ft rows spaced 8-in. apart. Roundup Ultra Max at 8 fl oz/a was used on June for weed control and Baythroid XL at fl oz/a on 4 August for insect control. All fungicide treatments were applied with a Lee Spider sprayer. The timing of fungicide application was designed to evaluate one spray at R ( August), unless soybean rust was present within mi. of the location prior to R. Plots were harvested on October. None of the treatments caused chemical injury on leaves, stems or pods. Cercospora blight was the only disease to show a significant reduction in disease by treatments (Table 6). Table 6. Soybean fungicide trial 7, Suffolk. Treatment and rate/a z Brown spot y (8 Sep) Cercospora blight y (8 Sep) Downy mildew y (8 Sep) % defoliation x Yield w (8 Sep) (bu/a) P-value of yield vs. check seed wt. (oz) v % purple seed stain v Check... 5. 6.5 a. 7.5 7.7 --.4857. LEM7 SC 9.6 fl oz.5.5 bc. 4. 8..99.4887.5 LEM7 SC 9.6 fl oz + YT669.8SC 4 fl oz + Induce.56 fl oz.....5 bc.5 4. 4..898.464. LEM7 SC 9.6 fl oz + Punch.EC fl oz... 7.. cd....79.484. YT669.98SC 6 fl oz + Induce.56 fl oz....8 4.5 b. 5. 6.4.744.4699. Punch.EC 4 fl oz... 8.5.8 b-d. 4.8..77.487. Punch.EC fl oz + Headline.9EC 4.5 fl oz + Induce.56 fl oz.....5 d..5 4.6.4546.474. Absolute 5SC 5 fl oz....5 4.5 b.5 48.8..757.4596. Quilt.67SC 4 fl oz + COC.5 fl oz (% v/v)... 6.5. b-d.5.8 5.4.5686.489. Headline.8EC 4.7 fl oz + Folicur.6SC. fl oz... 5.8. cd.. 7..99.54.5 P-value....886..4.4.66 --..59 z A single application was applied at beginning pod (R) on Aug. y Data are based on visual estimates of percentages of leaf area with disease. x Defoliation rating scale: =none, = no leaves on plants. w Yields are weight of soybeans with.5% moisture. Soybeans were harvested on Oct. v Random samples of seed were collected at harvest for determining seed wt and percentages of seed with purple seed stain. Means followed by the same letter(s) are not significantly different according to Fisher s Protected LSD at P=.5. Arcsine transformation of visual estimates of disease was made in analysis to determine statistical significance. Soybean rust was not detected at the test site. Sprays of Punch + Headline w/induce provided the most effective control of Cercospora blight, based on disease ratings on September 8. No treatment significantly delayed defoliation or increased yield. 8
Tidewater AREC, Suffolk, Trial 7 (Phipps). The variety, planting date, cultural practices, and location of this trial were the same as Trial 7. Fungicide treatments were applied with a Lee Spider Spray on August (R ). All fungicide treatments resulted in significant reductions in incidence of brown spot and Cercospora blight (Table 7). Soybean rust was not detected in the trial. Defoliation rating on 9 October was suppressed the greatest by treatments with Quilt plus COC. None of the treatments caused visible evidence of leaf, stem or pod injury. The trial was harvested on October. None of the fungicide treatments significantly increased yield. Table 7. Soybean fungicide trial 7, Suffolk. Treatment and rate/a z Brown spot y (9 Sep) Cercospora blight y (9 Sep) Downy mildew y (9 Sep) % defoliation x (9 Sep) Yield w (bu/a) P-value of yield vs. check seed wt. (oz) v % purple seed stain v Check... 8.8 a 8. a. ab 46. a. --.495 bc.8 a Domark.9ME fl oz... 6. bc 5. b.8 bc 8.8 bc 6..94.4964 a-c. bc Domark.9ME 4 fl oz... 6. bc 4. b-d.8 bc 4. ab..6.4986 ab.8 a-c Domark.9ME 5 fl oz... 4. cd. c-e. c 4. ab 9..886.485 bc. c Laredo EC 7 fl oz... 7. bc 4.8 bc.5 bc. bc..7795.587 ab. ab Folicur.6SC 4 fl oz... 8.8 b 4.5 bc. ab 46. a 6.6.847.464 c. a-c Quilt.67SC 4 fl oz + COC.5 fl oz... 4. cd. e.5 bc 7.5 c 4.7.67.499 bc. c Headline.8EC 6 fl oz + Folicur 4SC. fl oz... 4. cd.5 de.8 a. bc 9..799.4777 bc. a-c Absolute 5SC 5 fl oz.... d. de.8 bc 8.8 bc 5.5.588.57 a.5 bc Stratego 5EC fl oz + Induce.56 fl oz... 4. cd. c-e.5 bc 7.5 bc 4..6.57 ab.5 bc P-value......778.55.99 --..98 z A single application was applied at beginning pod (R) on Aug. y Data are based on visual estimates of disease incidence and leaf area affected. x Defoliation rating scale: =none, = no leaves on plants. w Yields are weight of soybeans with.5% moisture. Soybeans were harvested on Oct. v Random samples of seed were collected at harvest for determining seed wt and percentages of seed with purple seed stain. Means followed by the same letter(s) are not significantly different according to Fisher s Protected LSD at P=.5, except downy mildew was analyzed at P=.. Arcsine transformation of visual estimates of disease was made in analysis to determine statistical significance. 9
Tidewater AREC, Trial 7, Suffolk (Phipps). The field site was planted to Pioneer 95M5 on 4 May. The soil type was Suffolk loamy sand that was planted to cotton, peanut and corn in 6, 5 and 4, respectively. Plots were eight, -ft rows spaced 8-in. apart. Roundup Ultra Max at 8 fl oz/a was applied on June and July at fl oz for weed control. All treatments were applied using a Lee Spider sprayer at R on August. Plots were harvested on October with a small-plot combine. None of the treatments caused symptoms of chemical injury on leaves, stems or pods. Soybean rust was not detected in the trial. Brown spot, frogeye leaf spot, Cercospora blight and downy mildew occurred at low levels on 9 September, but were not believed to reduce yield (Table 8). All treatments significantly reduced incidence of Cercospora blight and brown spot based on percentages of leaf area with symptoms of disease on 9 September. Orthogonal contrasts of treatment yields to the non-treated check indicated that Folicur increased yield significantly (P=.85). Incidence of purple seed stain was found in trace amounts only, but the weight of seed was increased significantly by Folicur, Absolute, Stratego plus Induce, and Headline plus Folicur. Table 8. Soybean fungicide trial 7, Suffolk. % leaf area with disease (9 Sep) y Treatment and rate/a z Brown spot Cercospora blight Frogeye leaf spot Downy mildew % defoliation x (9 Sep) Yield w (bu/a) P-value of yield vs. untreated Wt./ seed (oz) Untreated....8 a. a.8..5 7. --.48 c Folicur.6SC 4 fl oz....8 b. b...5 49..5.569 ab Quadris.8SC 4 fl oz + COC.5 fl oz.... b.5 b..5.5.6.567.485 bc Quilt.67SC 4 fl oz + COC.5 fl oz....5 b.8 b.8.8 4.8 6.4.896.499 bc Absolute 5SC 5 fl oz.... b.5 b.5.8. 44...566 a Stratego 5EC fl oz + Induce.56 fl oz.... b. b... 4..4575.559 a Headline.8EC 6 fl oz + Folicur 4SC. fl oz...5 b. b... 4.6.59.58 a Laredo EC 7 fl oz... 5. b. b..5.5 8.7.77.4966 a-c Domark.9ME 5 fl oz.... b.5 b..8.5 6.6.989.4947 a-c P-value.....75.699.689.454.865 --.79 z A single application was applied at beginning pod (R) on Aug. y Data are based on visual estimates of disease incidence and leaf area affected. x Defoliation rating scale: =none, = no leaves on plants. w Yields are weight of soybeans with.5% moisture. Soybeans were harvested on Oct. Means followed by the same letter(s) are not significantly different according to Fisher s Protected LSD at P=.5. Arcsine transformation of visual estimates of disease was made in analysis to determine statistical significance.
Isle of Wight County, Trial 47, Carr farm (Phipps). Soil at the field site was Slagle fine sandy loam and planted to corn in 4 and 6 and soybean in 5. The variety was DP94M8 planted in rows spaced 8 in. apart on 4 May. Plots were 9-ft wide by -ft long and treatments were replicated in four randomized complete blocks. Cultural practices included Roundup Ultra Max at fl oz/a on 5 August for weed control and Baythroid fl oz/a for insect control. All fungicides were applied with a Lee Spider sprayer in a single application at beginning seed (R ) on August. Plots were harvested on October with a small-plot combine. None of the treatments caused symptoms of chemical injury to leaves, stems or pods. Soybean rust was not detected in the trial. All fungicide treatments resulted in significant suppression of brown spot and Cercospora blight (Table 9). All fungicide treatments, except Domark, showed significantly lower defoliation than the untreated check on 8 September. Table 9. Soybean fungicide trial 47, Isle of Wight County. % leaf area with disease (8 Sep) y Treatment and rate/a z Brow n spot Cercos -pora blight Downy mildew % defoliation x (8 Sep) Yield w (bu/a) P-value of yield vs. check Wt./ seed (oz) % purple seed stain v Untreated... 9.5 a.5 a.8 88.8 a. --.594.5 a Quilt.67SC 4 fl oz + COC.5 fl oz....5 c. b. 66. b.6.64.59. bc Stratego 5EC fl oz + Induce.56 fl oz....8 c.5 b.5 67.5 b.6.98.54. a-c Absolute 5SC 5 fl oz....5 c. b. 7. b 4.5.5.5545.8 c Headline.8EC 4.7 fl oz + Folicur. fl oz....5 c.8 b.5 65. b.9.975.558. c Domark.9ME 5 fl oz... 5. b. b.8 8.5 a 8..4887.549. ab P-value.....4.89..57 --.95.54 z A single application was applied at beginning pod (R) on Aug. y Data are based on visual estimates of disease incidence and leaf area affected. x Defoliation rating scale: =none, = no leaves on plants. w Yields are weight of soybeans with.5% moisture. Soybeans were harvested on Oct. v Random samples of seed were collected at harvest for determining seed wt and percentages of seed with purple seed stain. Means followed by the same letter(s) are not significantly different according to Fisher s Protected LSD at P=.5, except purple seed stain was analyzed at P=.. Arcsine transformation of visual estimates of disease was made in analysis to determine statistical significance.
Greensville County, Trial 57, Hawkins Farm (Phipps and Hu). Soil at the field site was Craven clay loam, and planted to soybean in 5 and 6. Seed of RT 545N were planted in rows spaced 8-in. apart on May. Standard practices for production of glyphosateresistant soybeans were followed after planting. Plots were -ft wide by -ft long and treatments were replicated in four randomized complete blocks. A single application of treatments was made with a backpack sprayer at beginning pod stage (R ) on August. Soybeans were harvested on 8 October. All treatments reduced incidence of brown spot and Cercospora blight significantly according to ratings on 9 September (Table ). Treatments did not cause any plant injury and did not have a significant effect on defoliation or yield. Seed weight was increased significantly by treatments with Absolute and Stratego plus Induce. All treatments suppressed purple seed strain significantly, except Domark. Table. Soybean fungicide trial 57, Hawkins Farm, Greensville County. % leaf area with disease (9 Sep) y % defoliation Treatment and rate/a z Brown spot Cercospora blight Downy mildew x (9 Sep) Yield w (bu/a) P-value of yield vs. check Wt./ seed (oz) Untreated... 5. a 4. a.5.5 5.8 --.449 cd.8 b % purple seed stain v Quadris.8SC 6 fl oz + COC.5 fl oz.... d. cd.. 6..944.47 d. cd Quilt.67SC 4 fl oz + COC.5 fl oz....8 d. d. 5. 6..78.4 d. bc Stratego 5EC fl oz + Induce.56 fl oz... 6. bc. bc..5 7.4.45.4589 ab. d Absolute 5SC 5 fl oz... 4. cd.8 c. 6. 6..78.46 a. d Folicur 4SC 4 fl oz... 6. bc. bc. 8.8 6..84.475 b-d. b-d Headline 5EC 6 fl oz... 4. cd.8 c..8.4..4547 a-c.5 cd Headline.8EC 4.7 fl oz + Folicur. fl oz....8 d. cd.8.5 7.8.844.4 d.5 cd Laredo EC 7 fl oz... 7.5 b. ab. 7.5 6..87.4475 a-d.8 b Domark.9ME 5 fl oz... 4. cd.5 cd..8.4.865.48 d. a P-value.....7.956.7.67 --.77. z A single application was applied at beginning pod (R) on Aug. y Data are based on visual estimates of disease incidence and leaf area affected. x Defoliation rating scale: =none, = no leaves on plants. w Yields are weight of soybeans with.5% moisture. Soybeans were harvested on 8 Oct. v Random samples of seed were collected at harvest for determining seed wt and percentages of seed with purple seed stain. Means followed by the same letter(s) are not significantly different according to Fisher s Protected LSD at P=.5. Arcsine transformation of visual estimates of disease was made in analysis to determine statistical significance.
Eastern Shore AREC, Painter (Rideout and Waldenmaier). The trials were conducted on a Bojac fine sandy loam soil (organic matter <%) at the Eastern Shore Agricultural Research and Extension Center, Painter, VA. Standard practices for weed and insect control were followed and trials were planted to V9N4RR. The conventionaltillage, full-season trial was planted on 6 June and the double-cropped trial was planted on 6 July following wheat harvest. Plots consisted of two, -ft rows spaced in. apart bordered by two non-treated rows. Treatments were arranged in a randomized complete block design with four replications. Treatments were applied with a CO -pressurized backpack sprayer which delivered gal/a at 4 psi. The spray boom had four Tee Jet 5 nozzles spaced 8-in. apart. Treatments were applied to the full-season soybeans on 8 August when 75% of the soybeans were at reproductive stage R and no-till soybeans on 8 September at stage R. Percent defoliation was evaluated in the full-season beans on 4 September. Soybeans were harvested and weighed on 8 November in full-season and November in double-cropped. A -seed sample was collected from each plot during harvest to assess seed weight and percent discolored seeds. Results Full Season Soybean Trial - Dry weather predominated throughout the season with precipitation amounting to.8,.7,. and.8 in. for Jul, Aug, Sep and Oct, respectively. Less than inch of rainfall occurred during the first four weeks in July and less than.4 inch of rainfall fell from mid-september to the end of October. Consequently, disease pressure was low and no differences in foliage retention, yields seed count weight were observed (Table ). Table. Soybean yields and percent discolored seed from a full-season soybean fungicide trial conducted at the ESAREC in Painter, VA in 7. Treatment (Rate/A) % Defoliation (4 Sep) Yield (bu/a) Seed wt. g/ seed Discolored Seed (%) Nontreated Control... 46.4.4 7.94 Quadris SC 6 fl oz + COC % v/v... 46 7..55 4.8 Quilt.66SC 4 fl oz + COC % v/v... 5 6..6 5.79 Quilt.66SC fl oz + COC % v/v... 4 4.8.88 7.77 Quilt.66SC 4 fl oz + Quadris SC fl oz + COC % v/v... 46 9.7.7 9.7 Quadris SC 6 fl oz + Tilt.6EC 4 fl oz + COC % v/v... 8.8.6.56 Stratego EC fl oz + Induce.5% v/v... 44 7.7.5 8.6 Headline EC 6 fl oz... 49 6...44 Headline EC 6 fl oz + Folicur 4SC. fl oz... 49 5...7 Folicur 4SC 4 fl oz... 54 7..4. Punch.EC fl oz + Headline EC 4.5 fl oz... 7.. 9.5 Punch.EC 4 fl oz... 45 7 9.8 4. Absolute 5SC 5 fl oz... 6 9.4.58.6 Laredo EC 7 fl oz + Induce.5% v/v... 56 8.. 6.4 Domark ME 5 fl oz... 8 8.8.6 6. LSD (P=.5)... 7.5 6.4.95.6 Means within each column followed by the same letter are not significantly different (P=.5, Fisher s LSD).
Double Cropped Soybean Trial Dry weather predominated throughout the season as in the full- season trial. Disease pressure was low and no differences in foliage retention or yields according to treatment were observed (Table ). No differences in seed count weight or percent discolored seed were noted. Table. Soybean yields and percent discolored seed from a double-cropped soybean fungicide trial conducted at the ESAREC in Painter, VA in 7. Treatment (Rate/A) Yield (bu/a) Seed wt. g/ seed Discolored Seed (%) Nontreated Control... 9.4 6.6.55 Quadris SC 6 fl oz + COC % v/v... 6.8 6.5 5. Quilt.66SC 4 fl oz + COC % v/v....7 6.65 7.89 Quilt.66SC fl oz + COC % v/v... 5. 6. 8. Quilt.66SC 4 fl oz + Quadris SC fl oz COC % v/v... 9.8 6. 8.6 Quadris SC 6 fl oz + Tilt.6EC 4 fl oz + COC % v/v....4 5.85 7.9 Stratego EC fl oz + Induce.5% v/v.... 6.6 8. Headline EC 6 fl oz... 9. 6. 8.6 Headline EC 6 fl oz + Folicur 4SC. fl oz... 4. 6.85 8.46 Folicur 4SC 4 fl oz.... 6. 7.7 Punch.EC fl oz + Headline EC 4.5 fl oz... 4.7 7.55 7.97 Punch.EC 4 fl oz.... 6.8.9 Absolute 5SC 5 fl oz... 6. 6. 8.6 Laredo EC 7 fl oz + Induce.5% v/v... 4.8 6.7 6.77 Domark ME 5 fl oz....4 6.5 7.6 LSD (P=.5)... 6.6.6 4.7 Means within each column are not significantly different (P=.5, Fisher s LSD). 4
Eastern Virginia AREC, Warsaw (Stromberg). Summary for 7 Soybean Fungicide Trials FULL SEASON (Table ) Soybean cultivar Vigoro V48N5RR Full season soybeans planted on 6 June 7 Herbicides: Python.9 oz/a + Dual. pint/a PPI Fertilizer: -6-6 per acre Postemergence herbicide: RoundUp qt/a on 5 July 7 Fungicide applications: Treatments applied at R on 7 August 7 Treatments applied at 4 and days after R applications were made on and 8 August, respectively. Insecticide: Warrior T.84 oz/a on August 7 for corn ear worm and stink bugs Plots were harvested on 7 October 7. Table. Soybean yields and seed weight from a full-season soybean fungicide trial conducted at the Eastern Virginia AREC at Warsaw in 7. Treatment in product fl. oz. / A Application Growth Stage 5 Seed wt (g) Bu/A (.5% H O) Non-treated... -- 6.85 8.9 Quadris.8SC 6 fl oz + COC.% v/v... R 6.7 57. Quilt.67SC 4 fl oz + COC.% v/v... R 58.6 44.98 Stratego 5EC fl oz + Induce.5% v/v... R 64. 5.4 Domark ME 5 fl oz... R 6.95 56. Headline.9EC 6 fl oz... R 64.8 49.68 Headline.9EC 4.7 fl oz + Folicur 4SC. fl oz... R 6.5 4.98 Folicur.6SC 4 fl oz... R 65.9 47.8 Laredo.EC 7 fl oz + Induce.5% v/v... R 64. 59. Absolute 5SC 5 fl oz... R 64.65 5.88 Punch.EC 4 fl oz... R + 4 da 6. 4.5 Punch.EC fl oz + Headline.9EC 4.5 fl oz... R + 4 da 6. 6.75 Folicur.6SC 4 fl oz... R + da 6.5 4.55 Stratego 5EC fl oz + Induce.5% v/v... R + da 6. 49.9 Absolute 5SC 5 fl oz... R + da 6.75 5.6 Quadris.8SC 6. fl oz + Alto SL 4 fl oz + NIS.5% v/v... R 6.5 57.8 Quadris Extra.4SC 4 fl oz + NIS.5% v/v... R 6.68 46.58 LSD (P=.5)... -- 5.99 4. Means are not significantly different (P=.5, Student-Newman-Keuls). 5
Eastern Virginia AREC, Warsaw (Stromberg). Summary for DC-Soybean Fungicide Trial 7 DOUBLE-CROPPED (Table 4) Cultivar: Vigoro V48N5RR Planted on July 7 no-tillage into wheat stubble Herbicides: Gramoxone pint/a on July 7 (burndown). Dual pint/a + RoundUp qt/a on August 7 Fungicides: Treatments applied at R on 6 August 7 Treatments following R at 4 and days were made on August and 6 September, respectively. Insecticide: Warrior T.84 oz/a on August 7 for corn ear worms and stinkbug Plots were harvested on November 7. Table 4. Soybean yields and seed weight from a double-cropped soybean fungicide trial conducted at the EVAREC in Warsaw, VA in 7. Treatment and rate/a Application Growth Stage % Harvest Moisture Seed Quality (-5) seed wt in g Bu/A.5% H O Non-treated... -- 9..6.4. Quadris.8SC 6 fl oz + COC.% v/v... R 8.95.68. 9. Quilt.67SC 4 fl oz + COC.% v/v... R 9..8.8 7.88 Stratego 5EC fl oz + Induce.5% v/v... R 8.65.8.78 6.8 Domark ME 5 fl oz... R 9..8. 8.6 Headline.9EC 6 fl oz... R 8.9.5.85 8. Headline.9EC 4.7 fl oz + Folicur 4SC. fl oz... R 9.48.9.8 9.68 Folicur.6SC 4 fl oz... R 8.7.8.7 6. Laredo.EC 7 fl oz + Induce.5% v/v... R 9.45.8.5.5 Absolute 5SC 5 fl oz... R 8.9.5.85 7. Punch.EC 4 fl oz... R + 4 da 8.8.98.8 8.5 Punch.EC fl oz + Headline.9EC 4.5 fl oz... R + 4 da 9.8.8. 8. Folicur.6SC 4 fl oz... R + da 9..9.8 7.58 Stratego 5EC fl oz + Induce.5% v/v... R + da 9..75.85 9.4 Absolute 5SC 5 fl oz... R + da 9.6.75.6.9 Quadris.8SC 6. fl oz + Alto SL 4 fl oz + NIS.5% v/v... R 8.7.78. 8.68 Quadris Extra.4SC 4 fl oz + NIS.5% v/v... R 9..68.5.58 LSD (P=.5)... --.78.4.7.45 Means followed by same letter do not significantly differ (P=.5, Student-Newman-Keuls). 6
Summary: Soybean Rust Incidence and the Response of Soybeans to Fungicides in 7. Soybean leaflet samples were collected from regional sentinel plots and 84 commercial fields for detection of soybean rust in 7.. Sentinel plots were located at the Tidewater AREC (Suffolk), Southampton County (Courtland), Eastern Shore AREC (Painter), Northampton County, Shenandoah County, Southern Piedmont AREC (Blackstone), Charles City County, Northern Piedmont AREC (Orange), Eastern Virginia AREC (Warsaw), and Virginia Tech Kentland Farm (Blacksburg).. The first outbreak of soybean rust, caused by Phakopsora pachyrhizi, was found in leaf samples from Isle of Wight County on 9 October; thereafter, the disease was confirmed in 9 counties and cities (Chesapeake, Gloucester, Isle of Wight, Matthews, Middlesex, Suffolk, Surry, Sussex, and Virginia Beach) 4. No loss of yield to soybean rust was expected since the disease appeared when soybeans were beyond growth stage R6 (full seed). 5. Above normal temperatures and below normal rainfall in July, August, and September suppressed yield and resulted in unfavorable conditions for soybean rust; except for 6 of days from July to Aug and 4 of 8 days from September to 8 October. 6. Dry weather stress during the season limited development of common diseases in soybeans throughout most of 7 (i.e. Cercospora blight, purple seed stain, brown spot, frogeye leaf spot, anthracnose, pod and stem blight, etc.). 7. Fungicide treatments with Headline, Absolute, Quadris, Quadris Extra, Quilt, Stratego, Punch, Folicur, Absolute, Domark, Laredo, Folicur, and Headline showed little or no effect on yield in nine replicated field trials in 7. 7