Phenological behaviour of Parthenium hysterophorus in response to climatic variations according to the extended BBCH scale

Considering the importance of ecological and biological traits in imparting invasive success to the alien species, the phenological behaviour of an alien invasive weed Parthenium hysterophorus was documented according to the extended BBCH scale in four different seasons. A phenological calendar was prepared using both two‐ and three‐ digit coding system, precisely describing the developmental stages of the weed. The phenological documentation is further supplemented with the dates corresponding to a particular growth stage, pictures of the representative growth stages and meteorological data of all the four seasons. Results revealed that the phenology of the weed altered in response to the changing temperature and humidity conditions but no apparent climatic condition could inhibit its germination or flowering. However, the emergence of inflorescence was highly sensitive to the temperature/photoperiodic conditions. Variations in the phenological traits of P. hysterophorus with changing environmental conditions explain the acclimatisation potential of the weed permitting its vast spread in the non‐native regions. Since the given phenological illustrations are accurate, unambiguous and coded as per an internationally recognised scale, they could be exploited for agronomic practices, weed management programmes, and research purposes. To evaluate the impact of environmental factors (temperature [T] and humidity [RH]) on the invasiveness of Parthenium hysterophorus, we documented the phenological stages of the weed in different seasons using BBCH scale. For this, various growth stages beginning from the dry seeds until the maturity of the plant, were observed and photographed. Phenology of the weed in season 1 and 4 was remarkably different as it involved the formation of rosette stage unlike in season 2 and 3. The outcome of the study is expected to be useful for devising strategies to manage this invasive weed.