Evaluation location: Idaho, United States
In 2007, the USDA-ARS sugarbeet program in Kimberly, ID, in cooperation with the BSDF created an artificial curly top epiphytotic through the release of viruliferous leafhoppers at the USDA-ARS North Farm in Kimberly, ID. The North Farm field had been in corn in 2006, and was plowed in the fall, roller harrowed, fumigated with Telone II at 20 gal/A, and roller harrowed again. The field was fertilized (120 lb N/A) on April 16, 2007 and roller harrowed. On April 27 the field was sprayed with Ro-Neet at 0.5 gal/A and roller harrowed. The farm as planted (density of 142,560 seeds/A) on May 23. The plots were two rows 10 ft long and 22 in row spacing and arranged in a randomized complete block design with two replicates. Those submitting the entries chose the number of replications they desired. The fields were sprinkler irrigated and hand weeded as necessary. The plant populations were thinned to 47,520 plants/A. The plants were inoculated at the 4-6 leaf growth stage on June 26 with 6 viruliferous hoppers per plant. The leafhoppers were moved twice a day (right after sunrise and just before sunset) for one week. The plants were sprayed with Lorsban 4E (1.5 pints/A) on July 10 to kill the leafhoppers. The plots were rated for symptom development using a scale of 0-9 (0 = healthy and 9 = dead; described in Plant Disease 91:1459-1463). DNA was extracted from three individual plants in both nurseries and tested with species specific primers to confirm the virus species present. Disease development was very good at both sites allowing for good separation on all three rating dates. The temperatures during the growing season were typical for the Kimberly area, except the nighttime temperatures were above average. DNA isolations revealed that all six plants tested contained all three Curtovirus species: BSCTV, Beet mild curly top virus, and Beet curly top virus.