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    The critical period for weed control in three corn (Zea mays L.) types
    (Elsevier Sci Ltd, 2016) Tursun, Nihat; Datta, Avishek; Sakinmaz, Mahmut Sami; Kantarci, Zekeriya; Knezevic, Stevan Z.; Chauhan, Bhagirath Singh
    Knowledge of the crop-weed competition period is vital for designing effective weed management strategies in crop production systems. Field studies were conducted at the Agricultural Research Institute, Kahramanmaras, Turkey in 2013 and 2014 to determine the critical period for weed control (CPWC) in three corn (Zea mays L.) types (field corn, popcorn, and sweet corn). A four parameter log-logistic model described the relationship between relative crop yield to both increasing duration of weed interference and length of weed-free periods. The relative yield of corn was influenced by duration of weed-infested or weed-free period, regardless of corn types. Increasing periods of weed interference significantly reduced corn yields in both years. In field corn, the CPWC ranged from 175 to 788 growing degree days (GDD) in 2013 which corresponded to V2-V12 growth stages, and 165-655 GDD (V1-V10 growth stages) in 2014 based on the 5% acceptable yield loss (AYL) level. In popcorn, the CPWC ranged from 92 to 615 GDD (VE-V10 growth stages) in 2013 and 110-678 GDD (V1-V10 growth stages) in 2014. In sweet corn, the CPWC ranged from 203 to 611 GDD in 2013 (V2-V10 growth stages) and 182-632 GDD (V2-V10 growth stages) in 2014. The practical implication of this study is that weed management should be initiated around V1 stage and maintained weed-free up to V12 stage in all corn types to prevent yield losses greater than 5%. These findings could help corn producers improve the cost effectiveness and efficacy of their weed management programs. (C) 2016 Elsevier Ltd. All rights reserved.
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    Nitrogen application influenced the critical period for weed control in cotton
    (Elsevier Sci Ltd, 2015) Tursun, Nihat; Datta, Avishek; Tuncel, Emine; Kantarci, Zekeriya; Knezevic, Stevan
    The critical knowledge of crop-weed competition period is important for designing weed management strategies in cropping systems. Field experiments were conducted in 2012 and 2013 growing seasons at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effect of three nitrogen (N) rates (0, 150 and 300 kg N ha(-1)) on the critical period for weed control (CPWC) in cotton. A four parameter log-logistic model was fit to the two sets of relating relative crop yield to data obtained from increasing durations of weed interference and lengths of weed-free period. In both the years and regardless of the N application rate, the relative yield of cotton decreased with increasing duration of weed-interference and increased with increasing duration of weed-free period. The application of N fertilizer delayed the beginning of the CPWC in cotton. At the 0 kg N ha(-1), the CPWC ranged from 44 to 537 GDD (growing degree days) (7-51 days after crop emergence [DAE]) in 2012 and 87-605 GDD (14 -57 DAE) in 2013 based on the 5% acceptable yield loss. At the 150 kg N ha(-1), the CPWC ranged from 124 to 597 GDD (18-56 DAE) in 2012 and 183-551 GDD (22-49 DAE) in 2013. Depending on the N application rate, weed-free conditions need to be established as early as one week after crop emergence and maintained as late as eight weeks after crop emergence to avoid more than 5% loss in cotton yield. These findings could help cotton producers improve the cost effectiveness and efficacy of their weed management programme under different N application rates. (C) 2015 Elsevier Ltd. All rights reserved.
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    Row spacing impacts the critical period for weed control in cotton (Gossypium hirsutum)
    (Springer, 2016) Tursun, Nihat; Datta, Avishek; Budak, Selvi; Kantarci, Zekeriya; Knezevic, Stevan Z.
    The knowledge on the critical crop-weed competition period is important for designing an efficient weed management program. Field studies were conducted in 2012 and 2013 at the Agricultural Research Institute, Kahramanmaras, Turkey to determine the effects of three row spacing (50, 70 and 90 cm) on the critical period for weed control (CPWC) in cotton. A four parameter logistic equation was fit to data relating relative crop yield to both increasing duration of weed interference and length of weed-free period. The relative yield of cotton was influenced by the duration of weed-infested or weed-free period, regardless of row spacing. In cotton grown at 50 cm row spacing, the CPWC ranged from 117-526 growing degree days (GDD) (V2-V11 growth stages) in 2012 and 124-508 GDD (V2-V10) in 2013 based on the 5% acceptable yield loss level. At 70 cm row spacing, the CPWC ranged from 98-661 GDD in 2012 (V2-V13) and 144-616 GDD (V2-V12) in 2013. At 90 cm row spacing, the CPWCranged from 80-771 GDD in 2012 (V1-V14) and 83-755 GDD (V1-V14) in 2013. In order to obtain a 95% weed-free yield, the weed management should start at 16 days after crop emergence (DAE) and continued until 52 DAE (V2-V11) for crops grown in 50 cm row spacing, 15 and 60 DAE (V2-V13) for 70 cm row spacing and 11 and 67 DAE (V1-V14) for crops grown in 90 cm row spacing. This suggests that cotton grown in narrow row spacing (50 cm) had greater competiveness against weeds compared with wider row spacing (70 and 90 cm). Cotton growers can benefit from these results by improving cost of weed control through better timing of weed management.