The late season 2004 BPMV analyses are complete and the season ended as it began, with minimal detection of BPMV in bean leaf beetles collected in spring alfalfa fields followed by no positive detections of BPMV in late season soybean plants throughout the state.
Bean Pod Mottle Virus – A No-Show in Wisconsin Soybeans in 2004
Bean Pod Mottle Virus – A No-Show in Wisconsin Soybeans in 2004
Eileen Cullen, Extension Entomologist
UW Entomology Department
Krista Lambrecht, Plant Pest and Disease Specialist –
Entomologist, WI DATCP
Annette Phibbs, Plant Pest and Disease Specialist –
Plant Pathologist, WI DATCP
In 2004, the University of Wisconsin Entomology Department and Wisconsin Department of Agriculture Trade and Consumer Protection (DATCP) shared research plot and statewide survey data on bean leaf beetle population density and distribution in relation to bean pod mottle virus (BPMV) incidence in Wisconsin soybeans. The late season 2004 BPMV analyses are complete and the season ended as it began, with minimal detection of BPMV in bean leaf beetles collected in spring alfalfa fields followed by no positive detections of BPMV in late season soybean plants throughout the state.
Bean pod mottle virus (BPMV), transmitted by bean leaf beetle, can reduce soybean yields between 3 and 52% (Gergerich 1999) with infected plants producing fewer, smaller and lower weight seeds, along with potential for a mottled seed coat discoloration. The adult overwintering bean leaf beetle population emerges in the spring to feed on wild and cultivated legumes, moving to early planted soybeans where they continue to feed and then deposit eggs of the first generation. First generation beetles give rise to second generation beetles appearing in August and responsible for pod clipping when populations are high. Second generation beetles become the overwintering population. Early planted soybeans, generally May 15th or earlier, can be particularly vulnerable to BPMV infection between the VC and V2 growth stages as this overlaps with the overwintered bean leaf beetle population moving from legumes into soybean.
The Wisconsin DATCP pest survey team conducted a spring survey of overwintered bean leaf beetle and BPMV in alfalfa. Twenty-eight contiguous counties in the southern third of Wisconsin were surveyed, with 102 alfalfa field sites total. Sweep net samples were conducted between May 17 and June 10, 2004. Bean leaf beetle numbers were recorded at each site, and beetles were returned to the laboratory and tested for BPMV using Enzyme-Linked Immunosorbent Assay (ELISA). Bean leaf beetle BPMV results were negative at 92% (94/102) of the sites. Negative results consisted of zero beetles collected at 39 sites, and bean leaf beetles without BPMV collected from 55 sites. BPMV positive bean leaf beetles were recovered from 8% (8/102) of the sites. These 8 positive results were restricted to first (6 sites) and second (2 sites) southern tier counties.
Wisconsin DATCP conducted a summer survey of 293 soybean fields throughout Wisconsin between July 19 and August 24, 2004. Bean leaf beetle samples were conducted in each field and beetles were returned to the laboratory and tested for BPMV by ELISA. In addition, trifoliate leaves were collected from 40 plants in each of the 293 soybean fields and returned to the laboratory to assess BPMV in soybean plants by ELISA. None of the bean leaf beetles collected in the July 19 – August 24 soybean survey tested positive for BPMV. Likewise, of the 293 soybean fields sampled in the statewide survey, none of the soybean plants tested positive for BPMV.
University of Wisconsin, Entomology Department established a bean leaf beetle and BPMV experimental plot in a southern tier county location at the RockCounty farm in 2004. One objective of the study was to investigate the interaction between bean leaf beetle population density in untreated plots and BPMV incidence in these plots following 1) overwintered bean leaf beetle population and 2) first generation bean leaf beetle population.
Plots were planted in 30-inch rows on May 3rd, 2004 with the soybean variety NK S19-V2. Plot dimensions were 4 rows (10 ft.) wide by 25 ft. long. The untreated plots were part of a larger efficacy trial planted in a completely randomized block design replicated four times. Plots were sampled weekly from May 25 (V1-V2 soybean growth stages) through August 19. Each week, population density was enumerated as bean leaf beetles per row foot (BLB/ft) using whole plant counts early season, then switching to drop cloth samples as soybean foliage developed. Soybean leaf samples were collected from 20 plants in each plot (n=80 plants) on June 29 when weekly bean leaf beetle samples indicated the overwintered population had declined, and first generation had not yet begun to build. Leaves were returned to the laboratory to assess BPMV in soybean plants by ELISA. Soybean leaf samples were again collected from 20 plants in each plot (n=80 plants) on August 17 after first generation beetles had developed and fed upon plants. Leaves were returned to the laboratory to assess BPMV in soybean plants by ELISA.
None of the June 29 soybean plant samples (0/80 plants) tested positive for BPMV. Likewise, none of the August 17 soybean plant samples (0/80 plants) tested positive for BPMV. These results indicate that BPMV incidence was very low during 2004, such that BPMV could not be detected in the UW Entomology soybean plant samples from overwintered population bean leaf beetle feeding or first generation bean leaf beetle feeding. Overwintered bean leaf beetle population density in the UW study peaked at only 0.5 BLB/ft. in the untreated plots on May 25th. First generation bean leaf beetle population density in this study peaked at 1.3
BLB/ft. in the untreated plots on July 27th. Both population densities remained well below defoliation treatment thresholds. Mean yield for the untreated plots in this study was 60.2 bushels/acre.
As expected, based on our intensive Entomology Department plot results and WI DATCP’s extensive statewide survey results, I’ve received no producer or seed company reports of green stem in the field during the 2004 harvest or mottled seed at storage. Future collaboration between UW Entomology and WI DATCP will continue to investigate the relationship between bean leaf beetle population densities, the proportion/distribution of BPMV infected bean leaf beetles, and proportion/distribution of BPMV infected soybean plants in Wisconsin.
Reference
Gergerich, R.C. 1999. Comoviruses: Bean pod mottle comovirus. pp. 61-62 in: Compendium of Soybean Diseases, 4th ed. G.L. Hartman, J.B. Sinclair, and J.C. Rupe, eds. American Phytopathological Society, St. Paul, MN.