Dawn Sikora

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Abstract Sunflower moth, Homoeosoma electellum, is a serious pest of oilseed and confection sunflowers. In this study, we determine efficacy of resistance against this pest. Thirty commercial hybrids, inbreds, and varieties of sunflowers were tested in replicated field and laboratory studies. Trait efficacy is determined by pericarp strength by means of physical compression tests and damage to achenes. Initial sunflower entries were planted May 2014 and data collection began in early August 2014. A second season was planted June 2015, with sampling beginning late August the same year. In 2014, oilseed varieties showed a strength average of 2.71 ± 0.11 N while confection varieties showed an average of 4.70 ± 0.07 N. Of the four varieties selected for inclusion in 2015, RH 841 had the highest pericarp strength estimate at 9.74 ± 0.24 N and HA 467 had the lowest pericarp strength estimate at 4.16 ± 0.24 N. Bioassay screening from field and greenhouse grown sunflowers provided a baseline pericarp strength of up to 5N for targeting in future sunflower host plant resistance trials. Results from choice feeding bioassays and infestation trials show HA 467 may be more susceptible to sunflower moth than RH 841, RH 1130 EX, and HA 441. Data from 2014 and 2015 suggests that RH 1130 EX may be a good variety to explore for future sunflower moth resistance traits and field hardiness. Additional data suggests that investigating thickness as a trait for sunflower resistance to sunflower moth may be advantageous. The objectives of this study are to: 1) Evaluate the rate of pericarp hardening in confection and oilseed sunflowers; 2) Evaluate the effect of pericarp hardening on sunflower moth larval feeding; and, 3) Evaluate the impact of sunflower moth resistance on sunflower yield components. Outcomes of these results will help sunflower producers reduce expenditures on chemical control measures and may reduce pest risk for earlier planting dates.