Brief Summary of Minutes of Annual Meeting

Jennifer Willems welcomed the group to the CDFA office in Clovis, CA. Rebecca Creamer explained a bit about the group and its purpose. Introductions were made, and the agenda was discussed. Carrie Wohleb presented the status of curly top and the beet leafhopper in Washington. Important crops that serve as hosts for the virus and hopper include dry beans, snap beans for seed production, crucifers, and sugarbeets for seed production. Watermelons are also produced and are hosts as is coriander grown for seed. She presented her guides for leafhopper identification, including the size (3 mm), and lacking dark spots on the head and wings. The worst curly top years for Washington were 2003 and 2013, however curly top damage is usually localized and can occur any year. The beet leafhopper also transmits beet leafhopper transmitted virescens agent (BLTVA) that causes problems on radish and potatoes (purple top). A survey showed that 9-40% of the leafhoppers carry BLTVA, while 0-50% of the leafhoppers were found to carry beet curly top virus. Common weed hosts of the leafhopper include tumble mustard Kochia, and filaree. She presented her sampling program for the beet leafhopper on potatoes, which includes trapping with yellow sticky traps from field margins from 45 locations, 2 traps/field, and changing traps weekly. She is using the data to develop a prediction model for disease based on trap catches. She can use the data to recommend systemic insecticides at planting and foliar insecticides later in the season. She also recommends treating weeds at the margins of fields using rangeland-specific herbicides. Tom Turini spoke about monitoring tomatoes for virus and leafhoppers in the 2013-2015 seasons in Fresno and Kings Counties of California. 2013 was a very sever curly top year, with some fields with up to 80% incidence in processing tomatoes. 2014 was a low curly top year, while 2105 was an intermediate year with up to 45% curly top in some areas. He is monitoring 23 sites in Fresno, Co. He found the most virus near the coast range, specifically in the Coalinga area or just east of Coalinga. The cropping system has changed somewhat in that all tomatoes are now started from transplants and the crop has moved from the western side of the Central Valley to the eastern side, to take advantage of more available irrigation water. He found high levels of BCTV in March planted tomatoes even though most were treated with neonicitinoid insecticides. Most varieties are highly susceptible, so that a specific variety does not contribute much to differences in incidence or symptom expression. Also disease distribution in fields was quite variable. In his 2015, he found by mid June, 13-34% had BCTV even with Admire at planting. The highest level found was 51% in Firebaugh on 26 June, 2015. In an insecticide trial he found the untreated had 14% disease, Verimark at the high level as a tray drench decreased disease to 5.7%, which Admire added to the transplant water gave 8% disease. Stephanie Walker discussed curly top disease in New Mexico. She presented the chile production practices, and provided the curly top management recommendations in chile. She also presented on trials for cultural control of curly top in tomatoes, and explained that the crop is primarily for farmers markets, so that organic controls are necessary. Eric Wenninger presented results from an insecticide trial for curly top in sugarbeet. He compared Poncho Beta as a seed treatment with Asana as a foliar with a combination of both insecticides. The combination significantly reduced curly top. However age-based resistance was very strong, kicking in around 11 weeks after planting, while Poncho Beta lasted until about 10 weeks after planting. Alex Karasev talked about curly top in Idaho that is a problem on sugarbeets and beans. He reported on testing isolates from the USDA sugarbeet nursery and found CFH, Cal/Logan and Worland strains. He also presented on a BCTV isolate characterized from chile isolated from Chihuahua, Mexico. He found that isolates were recombinants of mild and severe and could be similar to the LH71 isolate that Li Fang Chen had previously reported on. Bill Wintermantel reported on his testing for curly top strains in tomatoes and sugarbeets in California and Idaho. In 2103, curly top was really bad in Coalinga and the BCTV-CO was the primarily isolate. In sugarbeets in 2003 there were equal amounts of BMCTV and BSCTV, in 2007 all isolates were BSCTV, in 2013 all (and melons) were infected with what appeared initially to be BMCTV, but were similar to Drake Stenger’s (Colorado) CO-95. In Idaho in 2013 there was more BSCTV and lower levels of BMCTV. However what looked like BMCTV was not classic Worland, but instead was a Worland variant that also resembled CO-95, but clearly differed from the emerging variants in California. This supports the premise that new BCTV variants are emerging in California and displacing traditional forms of BCTV. Bill also reported on competition experiments between different virus strains inoculated by either agroinoculation of infectious clones or leafhoppers. The clone of BMCTV was not as effective, so it was inoculated using 15 leafhoppers/plant. Successful competition experiments compared CFH and BV3 on sugarbeets and tomatoes by adding the same amount of each infectious clone together using agroinoculation. Rebecca Creamer presented information on the relative levels of curly top strains in chile and weeds from 2001 through 2015. PeYDV was detected in 2001 and 2003 with higher levels compared to BCTV-mild or BCTV-Svr NM. PeCTV was discovered in 2005 and levels have increased such that 77% of the chile tested in 2015 had PeCTV. Tesneem Nusayr presented experiments indicating that the beet leafhopper endosymbionts contain GroEL and that the GroEL from E. coli will nonspecifically bind to virus coat protein. Additional binding experiments are underway. Li Fang Chen has begun work toward obtaining the genome sequence of the beet leafhopper. Her first experiments were to determine the size of the genome. She used flow cytometry and monitored using propidium iodide-stained nuclei from the heads of the leafhoppers. She found a an average size of 648 MB for female hoppers and 632 MB for males. Bob Gilbertson gave an update on the analysis of the 2013 curly top outbreak in CA. He explained the survey system and that the outbreak was the result of high populations of leafhoppers and high titer of virus within the leafhoppers, which occurred in 2003 and 2013. With the very large numbers of leafhoppers collected, the hoppers were pooled in groups of up to 30 for testing for BCTV by PCR using strain-specific primer sets. Many weeds were collected and tested for virus also. The most highly prevalent strains were BCTV-CO and BCTV-LH71. Very surprising, but they also found BCTV-SpCT (spinach curly top) in tomato and pepper, which had not been found previously in California. Testing from Imperial Valley, where sugarbeets are still grown, showed that CFH is still predominant in that area. Bob also talked about efforts to develop/test curly top-resistant tomatoes. They tested tomato varieties that contained the Ty genes, that work against begomoviruses. They crossed the begomovirus-resistant tomatoes with processing tomato lines and found that the F1 lines gave good curly top resistance, but not good marketable qualities. He found that the Ty1 and Ty3 genes are semidominant, the Ty5 gene is recessive, and more recently that the Ty2 gene is semidominant, which explains why the breeding efforts have been so difficult. Jennifer Willems gave an update on the curly top problem in California and the control board management efforts. For updates on BCTV control in California, subscribe to BCTV at http://www.cdfa.ca.gov/subscriptions/. Filaree, peppergrass and plantago are the primary overwintering weed hosts for the leafhopper and hopper numbers were slightly high (7-10/10 sweeps) on these plants in January. This triggered a winter spraying at the end of January. Winter spraying has been relatively rare, but was deemed necessary to prevent a repeat of the problems in 2013. Crews conducted sweeps with a sweep net from March-May. When large numbers of adult BLHs 30s-50s/10 sweeps are found the first week of March in Fresno Co., spraying was done within a week. Similarly, spraying was initiated in Kern Co at the end of March. Of the 117 BLH samples collected and the 286 symptomatic tomatoes tested, both were 82% were + for curly top virus. There were several thoughts about questions that still need to be answered. Where should yellow sticky traps be place and how do the trap results correlate with sweep net counts? How does the movement of leafhoppers change with seasons? What are the landing rates of leafhoppers in different environments and what influences the attractiveness of different plant types and plant distributions? How far away do the leafhoppers move? What is the effect of weeds on leafhopper movement? There was a brief discussion as to the 2016 meeting location and a suggestion was made to hold the meeting in Wyoming if a host could be identified.

Collaborative curly top projects for 2014-15 were carried out among Li-Fang Chen (Robert Gilbertson), Jennifer Willems (CDFA), Bill Wintermantel, and Tom Turini. Cooperative projects were carried out between Carl Strausbaugh, and Bill Wintermantel and between Carl Strausbaugh and Alex Karasev.

The group did not publish a report together.