Evaluation location: Idaho, United States
In 2008, 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 2007 and plowed in the fall. The field was fertilized (135 lb N/A and 120 lb P2O5/A) on April 29, 2008 and roller harrowed. The North farm was planted (density of 142,560 seeds/A) on May 19. The plots were two rows 10 ft long and 22 in row spacing, replicated twice and arranged in a randomized complete block design. 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 rating dates and data from the last, most severe rating (July 23) were used. The temperatures were below normal early in the growing season but were above normal around hopper release. DNA isolations revealed that all six plants tested contained all three Curtovirus species: BSCTV, Beet mild curly top virus, and Beet curly top virus.