Beet leafhopper and BCTV strain survey 2022 progress report

Authors: Strausbaugh, Carl; ERIC, WENNINGER - University Of Idaho; Jackson, Laurie; Vincill, Eric

Submitted to: The Sugarbeet
Publication Type: Trade Journal
Publication Acceptance Date: 1/5/2023
Publication Date: 3/6/2023
Citation: Strausbaugh, C.A., Eric, W., Jackson, L.K., Vincill, E.D. 2023. Beet leafhopper and BCTV strain survey 2022 progress report. The Sugarbeet. p.50-52.

Interpretive Summary: Beet curly top virus (BCTV) almost eliminated sugar beet production in the western United States in the 1920s and early 1930s until resistant cultivars were developed. However, commercial sugar beet cultivars only contain low to intermediate resistance. In order to maintain proper resistance to BCTV in cultivars, the strains present in southern Idaho should be monitored on a regular basis both in plants and the beet leafhopper vector. At the request of a sugar beet industry stakeholder, beet leafhopper (BLH) populations in southern Idaho were tracked during the 2020 (4 counties) and 2021 (5 counties) growing seasons in desert areas and sugar beet and dry bean fields in southern Idaho. BLH populations in Elmore Co. were present in at least double-digit numbers per sticky card each week at all sites through most of the summer both years. BLH were evident by mid-summer in Owyhee Co. and by late in the summer in Twin Falls and Bingham Co., but they were almost undetectable in Minidoka Co. Vertical card placement was preferable since horizontal placement reduced captures by 45 to 75%. Sequencing the cytochrome oxidase gene identified that two haplotypes were dominant within the BLH population. Beet curly top virus (BCTV) was detected in 42% of the BLH samples in 2020 and 67% in the 2021 samples. The Worland strain of BCTV was dominant both years in the BLH population, but the BCTV strains found in the plant samples were more of a mix. A number of BLH samples and plant samples were positive for the BCTV coat protein gene, but negative for strain specific primers evaluated to date. Once all data are collected, the project will establish the BCTV strains for which host plant resistance is needed and the best time for when control of BLH is necessary.

Technical Abstract: At the request of a sugar beet industry stakeholder, beet leafhopper (BLH) populations in southern Idaho were tracked during the 2020 (4 counties) and 2021 (5 counties) growing seasons in desert areas and sugar beet and dry bean fields in southern Idaho. Samples were collected on a weekly basis from mid-April through mid-September to assess all leafhoppers for population levels and the presence of Beet curly top virus (BCTV) strains. Crop plants from monitored fields were also assessed for the presence of BCTV strains. Once BLH populations in Elmore Co. began increasing in May, they were present in at least double-digit numbers through most of the summer at all sites both years. Thus, BLH numbers at desert sites in other areas were at or near zero, except for Owyhee Co. in 2021 late in the summer. Local weed populations appeared to be the primary source of BLH in crop fields and not desert sites. Two haplotypes (based on cytochrome oxidase gene) dominated the BLH population both years and were present in all areas of southern Idaho. Over the 22-week collection period, the horizontal card averaged 45 to 75% fewer BLH than the vertical card indicating vertical card placement is preferable. In 2020, 42% of the BLH samples were positive for the BCTV coat protein gene and in 2021 67% of the samples were positive. The Worland strain of BCTV was dominant both years in the BLH population, but the BCTV strains found in the plant samples were more of a mix. Phytoplasma has been detected in a few BLH samples, but all plant samples tested to date have been negative. Once all data are collected, the project will establish the BCTV strains for which host plant resistance is needed and the best time for when control of BLH is necessary.