Brief Summary of Minutes of Annual Meeting

Carl Strausbaugh welcomed the group to the Kimberly, ID, USDA station and explained a bit about the group and its purpose. Introductions were made, and the agenda was discussed. Alexander Karasev discussed the molecular tools that his group uses to screen sugarbeet resistance to curly top. BMCTV, BSCTV, and BCTV are the curly top strains generally found in Idaho. Their group approach is to screen for resistance to the three virus strains as well as to leafhoppers Plant resistance is quantitative and difficult to distinguish from leafhopper resistance. To be able to screen for virus resistance separately, they made infectious clones to each of the three different virus strains and infected sugarbeets with one of the clones or added leafhoppers. They made both 1.8mer and 1.2mer constructs for BSCT and BCTV, using similar methods to those of Li-Fang Chen, and used agroinoculation to introduce each construct into Nicotiana benthemiana and into sugarbeet. Early results showed that Monohikari variety sugarbeet was susceptible to all the clones (both 1.8mer and 1.2mers) tested. Sugarbeet variety KDH 13 was resistant to BSCTV and susceptible to BCTV. Alex also presented work on curly top identified on chile pepper in Delicias, MX (which is south of Chihuahua City within Chihuahua State) in 2010. They showed that 11/94 symptomatic plants contained curly top by ELISA suing the antisera that his lab produced. The cloned and sequenced four of the plants confirmed by ELISA. All were a BMCTV/BMCTV recombinant where the C4 gene is from BSCTV and the rest is BMCTV. Carl Strausbaugh gave an overview of curly top epidemiology in Idaho and discussed his program of seed and foliar insecticide treatments to control the leafhopper. All of his publications are available at http://eprints.nwisrl.ars.usda.gov/view/cv/Carl_A=2E_Strausbaugh.date.html. There are three leafhopper broods per year in Idaho. The leafhoppers overwinter on mustards in the desert. Initial migration of leafhoppers occurs from May 12 – June 5 with a peak around June 25 in southcentral Idaho. Carl runs the BSDF Curly Top Nursery where sugarbeet varieties are tested for resistance under severe disease pressure. Disease is rated on a 0-9 scale where 9 is a dead plant. Most varieties have a rating of 4.5-6.8 during the nursery screening. Their ratings are comparable with those from the commercial nurseries. Carl has extensively tested sugarbeet seed treatments with insecticides. Second generation neonicitinoids provide lengthy consistent protection for at least 59 days after planting. Seed treatment with Poncho Beta will even potentially allow the cultivation of a highly susceptible cultivars. Seed treatment is now mandated for western Colorado. Seed treatment with NipsIT and Cruiser, which are also 2nd generation neonicitinoids show similar efficacy to that of Poncho. Foliar insecticide treatments alone did not work as well as the seed treatments. Scorpion, a neonicitnoid foliar spray, worked, but not for very long, since it is photosensitive. Foliar sprays applied a week before and a week after releasing hoppers in late June were somewhat efficacious, particularly Asana and Mustang, which are pyrethroids. Poncho Beta also helped with control of leafminer reduced populations of black bean aphid, and root aphid (Pemphygus betae), and helped with extended storage of sugarbeet. Not surprisingly, sugarbeet with less curly top virus had better root storage. Carl also presented data from his curly top species survey. He found that in 2006 Colorado, Idaho, Montana, and Wyoming had BMCTV, BSCTV, mixtures of the two and Idaho also had some BCTV. In 2012 and 2013, Treasure Valley, ID had BMCTV and BCTV, while Magic Valley had only BMCTV. Neither had BSCTV. In 2013, the nursery survey had only BSCTV and BCTV, even though the leafhoppers began with BMCTV also. Li Fang Chen presented an overview of the current status of curly top virus taxonomy, a summary of the disease problems in the Central Valley of CA in 2013, and her work on characterization of recombinant viruses and symptom determinants in curly top viruses. She has monitored tomato plants and leafhoppers for curly top virus titer and strains since 2003. She has found three important recombinants that appear to be stable in the environment. First, BCTV-PeCT-BV3 was found in CA in tomato in 2009 and it is most closely related to BCTV-PeCT-NM isolate identified in New Mexico. The C4 and C1 ORFs are identical to those of BSCTV, while the rest of genome is similar to BCTV-PeCTV-NM, which is a distinct strain from other known BCTV strains. Second, LH71, identified from leafhoppers collected in California in 2010, has recombinant genome of BSCTV/PeCTV (C4 and C1) and BMCTV (rest of the genome). LH71 is most closely related to BMCTV but remains to be a distinct BCTV strain. Third, BCTV–CO was initially found in Colorado, but several representative isolates identified in California in 2013 are most closely related to BCTV-CO. The recombinant genome of BCTV-CO has C2 and C3 of BCTV-PeCT-BV3 and the rest is BMCTV. Li-Fang showed the region of C1/C4 gene is the symptom determinant. She made reciprocal mutant of LH71 and showed that mutant with BMCTV C1/C4 region induced symptom phenotype like BMCTV, whereas LH71 contains PeCTV/BSCTV C1/C4 had severe symptom phenotype on N. benthemiana, which was evident as severe stunted growth and vein swelling on tobacco. In 2013, which as a severe curly top year, large numbers of leafhoppers were collected early during the year (March) and those were found to contain high amount of viruses. Following the virus detection in leafhoppers, Li-Fang detected 96% of ~200 plant samples collected from Central Valley were BCTV positive and further found 65% of those were BMCTV and 77% of those BMCTV-positive samples were the BCTV-CO recombinant. There were 48% of the plant samples contained BSCTV and 65% of those were the LH71 recombinant. Overall the results showed the majority of viruses involved in the curly top disease outbreak in 2013 were the recombinant viruses-BCTV-CO and BCTV-LH71. Rebecca Creamer presented information on the beet leafhopper and its epidemiology in New Mexico associated with chile pepper. London rocket and Kochia are the key overwintering hosts and oversummering hosts, respectively, in New Mexico. Leafhoppers appear to be able to carry out their entire life cycle on the two plants if there are sufficient fall rains to bring up the winter annuals before the Kochia dies down. Leafhoppers prefer weeds from fallow fields over those from pecans or ditch banks. Larger numbers of leafhoppers were trapped at the margins of fields with abundant nearby weeds than those with smaller numbers of weeds and the leafhoppers were caught on the traps closest to the weedy areas. In fields without high weed pressure, leafhoppers were trapped on different location traps throughout the season. Mapping disease within a chile field, even those close to a weed source, showed a random distribution of infected plants. Jennifer Willems gave an overview of the curly top problem in California and the control board management system. For updates on BCTV control in California, subscribe to BCTV at http://www.cdfa.ca.gov/subscriptions/. In CA, fialree, peppergrass and plantago are the primary overwintering weed hosts for the leafhopper. Crews conduct sweeps with a sweep net from March-May. If 10-15 adult BLH/10 sweeps are found, then spraying is instituted. Spring insecticide treatments are made with a fixed-winged aircraft using malathion. Spring treatments are timed to kill nymphs before they move into the valley crop land. In June-August, the crews monitor leafhoppers on crop plants and weeds such as Russian thistle, goosefoot, and Bassia. Leafhopper are monitored Sept-November on fallow ground. Malathion is used both in spring and fall using aerial applications. Ground rig treatment applications are supplementary to aerial applications. Both aerial and ground rig applications are timed to knock numbers down prior to the beet leafhopper migrations in spring and fall. 2013 was one of the worst years for the disease in tomatoes in the Central Valley of California since the 1990s. Losses in tomatoes were approximately $100 million. 2013 was a dry mild winter with sporadic rain. There were already high leafhopper nymph counts in January, ~ 70/sweep. Sprays began at the end of March which is somewhat early. Infection of tomatoes occurred from April to harvest, ie. the entire season. There were problems with high numbers of leafhoppers on non-treatable land (for organic cattle production). Endangered species also limits the spray program. 2014 also had a very dry winter and few hoppers were found, and they were on poor hosts such as Atriplex. The salt bush was infected with curly top. They used yellow sticky traps in historical BLH hot spots to get a better handle on leafhopper numbers. Normal hopper counts were found in April, 10-20/10 sweeps. Aerial spraying began April 16. Due to the drought and water restrictions, there are many fallow weedy fields. The program tried several organic products for leafhopper control that could potentially find use in non-treatable areas. While they worked reasonably well- they were applied using a backpack sprayer and could be difficult to gear up for large scale spraying. There was a brief discussion as to the 2015 meeting location and suggestions were made to hold the meeting in Cody, Wyoming.

Collaborative curly top projects for 2013-14 were carried out between Rebecca Creamer and Li-Fang Chen (Robert Gilbertson), and among CDFA (Jennifer Willems), Bill Wintermantel, and Li Fang Chen (Robert Gilbertson). 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.