Growth and development of smooth pigweed (Amaranthus hybridus) emerged at different times of the year

ABSTRACT: Successful chemical weed control requires applying the herbicide when the weed is still small. However, the rapid growth of Amaranthus species makes the time window between emergence and maximum controllable size shorter, making their management difficult. Little is known about the Amaranthus hybridus growth rate under the edaphoclimatic conditions of South America. Therefore, this study defined the daily growth of A. hybridus in different emergence times. Smooth pigweed plants were established in November 2020, December 2020, and January 2021. Plants were measured every two days, and the entire development cycle was monitored. A. hybridus plants that emerged in November had higher plant height, on average, 227 cm, and higher dry mass, around 909.5 g plant-1. Plants that emerged in January were shorter, reaching around 197 cm, and had a lower dry mass, that is, on average 296.5 g plant-1. However, plants that emerged in January had a higher daily growth rate. Flowering occurred between 30 and 56 days after sowing, with an accumulated thermal sum of 468 to 926 degree-days. The A. hybridus growth rates were 2.47, 2.5, and 2.98 cm day-1 for emergence in November, December, and January, respectively.