Seed Production after Floret Removal from Sunflower Heads

The banded sunflower moth ( Cochylis hospes Walsingham; Lepidoptera: Cochylidae) is a pest of sunflower ( Helianthus annuus L.) in the northern Great Plains. Larvae feed initially on sunflower florets and subsequently on immature and matue seeds (achenes). Our objective was to measure the compensatory ability of sunflower for increasing seed yield in response to the loss of florets caused by floret and seed feeding of the banded sunflower moth for the accurate computation of economic injury levels. Treatments were removal of floret at 10% increment intervals from 0 to 50% of the florets of sunflower heads (capitula) at flowering. Floret removal had a direct effect on the number of resulting fertile seeds. Reducing the number of florets by 10% resulted in a 20% decrease in the number of fertile seed, an 18% decrease in total seed weight of the head, and a 22% decrease in seed volume. Comparable decreases were found in the number of fertile seeds for other increments of floret removal. The sunflower plant can compensate for floret removal by increasing the weight of individual seeds. As percent of floret loss increased, seed weight increased, but even when only 10% of the florets were destroyed, the weight gain did not overcome the subsequent loss of seeds. Oil content of seeds significantly decreased as floret loss increased. In addition to consumption of mature seeds, simulation of damage showed that early feeding by banded sunflower moth larvae on florets can also directly and indirectly affect the final yield of infested plants.