Yields of maize as related to the duration of Echinochloa crus-galli and Amaranthus retroflexus in maize stands.
In microplot trials in SW Poland, E. crus-galli and A. retroflexus competed strongly with maize, affecting its growth and yield. Exposure to these weeds for 2-6 weeks after emergence reduced maize yields by 7-50%, while exposure up to harvest resulted in a 70% reduction. Both species were the most competitive when at the 2- to 4-leaf stage. The need for control to be undertaken before this stage is stressed.