Phenological growth stages of <i>Amaranthus palmeri</i> according to the extended <scp>BBCH</scp> scale

Abstract Amaranthus palmeri S. Watson is a problematic weed that has been encountered almost all over the world because of its stronger adaptability, which causes huge economic losses and local plant diversity decline. As an invasive plant, A. palmeri has been found throughout China. We thus make a code system to describe the phenological growth process of A. palmeri according to the extended BBCH scale to better understand the phenological growth of this weed in China. The growth process of A. palmeri was divided into vegetative growth phases and reproductive growth phases. The vegetative growth phases are composed of seed germination (0), leaf development (1), formation of side shoots (2) and main stem elongation (3). Likewise, the reproductive growth phases include inflorescence emergence (5), blooming (6), fruit development (7), seed maturity (8) and senescence (9). Based on the extended BBCH scale, the first digit stands for the primary growth stages, and the third digit represents the secondary growth stages. In particular, the second digit defines the growth progress: the number 0, means the vegetative growth phases, and the number 1 stands for the reproductive growth phases. Owing to the fact that its seed can germinate multiple times within a year, a general illustration of the phenological development stages of A. palmeri germinating in different months was provided here to describe the growth dynamic characteristic at different times. These data are of great significance to develop effective strategies for weed control and management of A. palmeri .