Determination of the critical period of weed control in corn using a thermal basis

Field studies were conducted over 3 years in southeast Buenos Aires, Argent ina, to determine the critical period of weed control in maize (Zea mays L, .). The treatments consisted of two different periods of weed interference, a critical weed-free period, and a critical time of weed removal. The Gomp ertz and logistic equations were fitted to relative yields representing the critical weed-free and the critical time of weed removal, respectively. Ac cumulated thermal units were used to describe each period of weed-free or w eed removal. The critical weed-free period and the critical time of weed re moval ranged from 222 to 416 and 128 to 261 accumulated thermal units respe ctively, to prevent yield losses of 2.5%: Weed biomass proved to be inverse to the crop yield for all the years studied. When weeds competed with the crop from emergence, a large increase in weed biomass was achieved 10 days after crop emergence. However, few weed seedlings emerged and prospered aft er the 5-6 leaf maize stage (10-20 days after emergence).