Yield and yield components of imidazolinone-resistant sunflower (Helianthus annuus L.) are influenced by pre-emergence herbicide and time of post-emergence weed removal

With an increase in the use of imidazolinone (IMI)-resistant sunflower, it is important to determine the influence of weed interference and herbicide presence on seed yield and yield components of sunflower. The objective of this study was to determine the effect of different periods of weed presence on seed yield and yield components of IMI-resistant sunflower grown with and without ore-emergence (PRE) herbicide. Field studies were conducted in 2008 and 2009 at three locations in Serbia and one location in Nebraska, USA. A four-parameter log-logistic model described relationship between the crop yield and yield components to increasing duration of weed presence. Sunflower yield and yield components varied between years and among locations. Increasing periods of weed interference decreased yield and yield components of sunflower; however, the reductions were greater without PRE herbicide compared to the PRE herbicide treated plots. The length of time weeds could remain in the crop grown without PRE herbicide ranged from 14 to 26 days after emergence (DAE), which corresponded to the V3 (three leaves) to V4 growth stages on the basis of the 5% acceptable yield loss level. The duration of time that weeds could remain in the crop grown with PRE herbicide ranged from 25 to 37 DAE, which corresponded to the V6-V8 growth stages of sunflower. Practical implication of this study is that post-emergence weed control in IMI-resistant sunflower grown with PRE herbicide can be delayed approximately by two weeks compared to the crop grown without PRE herbicide. (C) 2012 Elsevier B.V. All rights reserved.