Mechanical weed control strategies for grain amaranth (Amaranthus cruentus L.)

Currently, no herbicide is registered for grain amaranth in Europe, the United States and South America. Hence, weed control must be addressed with alternative methods. Field trials were conducted in 2018 and 2019 in Central Italy by comparing some mechanical weed control treatments in grain amaranth (Amaranthus cruentus L.). In 2018, the five treatments were: untreated control (T118), cutter hoeing (T218), flat share cuts and one central duck foot tine (T318), flat share cuts and two central duck foot tines with second operator (T418), and three duck foot tines (T518). In 2019, the five treatments were: untreated control (T119), three duck foot tines (T219), flex tine harrowing (T319), flex tine harrowing plus finger weeding with red fingers (T419), and finger weeding with red fingers (T520). In 2018, amaranth was a successful competitor against weeds from 40 days after emergence (10 true leaf stage, corresponding to BBCH code 15). The competitive ability was showed by excellent seed yields averaging 1.2 t ha-1, for all treatments. This characteristic was also confirmed to some degree in 2019. However, seed yield in 2019 was more strongly influenced by treatment as well as by the lower emergence of plants. All the mechanical methods employed can be effectively used for weed control in grain amaranth. Treatments with the flex tine harrower and finger weeder negatively affected the plant density at harvest, necessitating further optimization. However, combination mechanical strategies proved the most effective, especially in controlling dicot weeds. There is a need to optimize strategies, with mechanical equipment, to anticipate and improve the ground cover of amaranth. These strategies include selecting optimal plant density and the correct distancing between the rows for easier mechanical control.