Response of sunflower plants to physical injury

Injury to sunflower (Helianthus annuus L.) caused by hail and pests can result in financial losses to producers. This field study was conducted to determine the response of sunflower to different types and levels of physical injury. The information will assist producers in deciding whether to replant or maintain a crop. Studies were conducted at four North Dakota locations. Treatments consisted of stand reduction, terminal bud removal, and top one third of the plant cut off, imposed on either 25 or 50% of an established plant population at five stages of plant development. Plant response to injury varied among treatment stages. When plants were injured at vegetative stages V4 and V8, 98.2 and 93.2% of the treated plants produced multiple branches and heads. When plants were injured during the transition from vegetative to reproductive development (V12, R1), a greater proportion (26.1 and 20.6%, respectively) of the plants died. The majority of the plants injured at stages R1 and R3 neither died nor branched (55.5 and 96.1%, respectively); they continued to live but did not produce seed. Living injured plants reduced total crop yield more than the injured plants that died, since living injured plants continued to compete with uninjured plants for space, light, nutrients and moisture but did not contribute toward yield. Key words: Sunflower, Helianthus annuus L., hail, crop injury