Simulated Hail Research in Sunflower: Defoliation1

Abstract

AbstractAccurate loss procedure and compensation due to hail losses are a major concern to both the producer and the insurance company. Field experiments simulating leaf loss such as that which would occur as a result of a hail storm were conducted on hybrid sunflower (Helianthus annuus L.) at Carrington and Fargo, ND. The objective of this study was to investigate the agronomic response of sunflower to various levels of defoliation applied at different stages of plant development. Defoliation treatments (0, 25, 50, 75, and 100% of the leaves randomly removed with a knife) were applied at nine stages of plant development from V4 through R7. Fifty, 75, and 100% defoliation averaged across all developmental stages decreased seed yield significantly compared to the check. Seventy‐five and 100% defoliation decreased seed yield significantly compared to the check when treatments were applied at the R1 through R6 stages. Plant death often resulted when treatments of 100% defoliation were applied at stages R3 and R4. Oil percentage decreased significantly with 100% defoliation at the R4 through R7 stages. One‐hundred‐percent defoliation averaged over all stages of plant development decreased oil percentage an average of 11.9%. One‐hundred‐percent defoliation averaged across all stages of plant development decreased head diameter, plant height, percent stem breakage; days to R5.5, and achene weight. Complete removal of leaves at the reproductive (R) stages of plant development affected the variables measured to the greatest degree. As defoliation percentage decreased, values of variables measured were affected to a lesser degree.