Russian knapweed (Acroptilon repens) is a perennial and noxious weed. This experiment was conducted to determine phonological stages and their duration in an experimental plot based on degree-days. The Results indicated that emergence of root occurred in 0 degreedays, until 3823.3 and 8 phenological stage was recorded. These stages were shoot emergence from root, changing rosette to main stem, secondary shoot producing, main stem branching, bloom stage, flowering, flower drying and shoot yellowish. This study showed that the seeds of Russian knapweed could identify in bloom production stage. Seeds turned into milky stage at 10 days and matured at 30 days after blooming.

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