The competitive ability of Chenopodium album and Echinochloa crus-galli in maize crops depending on the time of their occurrence or removal

Small-plot experiments for two levels of infestation (20 and 40 plants per m2) with Chenopodium album L. and Echinochloa crus-galli (L.) P. Beav were conducted in the 2009–2011 seasons. In the first variant, the effect of time of weed removal on maize was investigated. Weeds were removed in the following growth stages of maize: one, three, five, and seven leaves, the beginning of stem elongation, and the stage from the fourth to sixth node. The second variant concerned the effect of time of weed emergence on maize and included the same maize growth stages as mentioned above. In both treatments, weed competition was compared to the control – the plot completely free from weeds, as well as to the plot fully covered with weeds. Echinochloa crus-galli in the amount of 20 plants per m2, which were not removed until the five-leaf stage or which emerged immediately after the seven-leaf stage of maize, did not show any competitive effect on the growth and development of maize. Chenopodium album was characterized by a similar effect at the same level of weed infestation severity and when not removed until the five-leaf stage as well as in the case of plants that emerged after the seven-leaf stage of maize. Both species present in an amount of 40 plants per m2 needed to be removed no later than at the three-leaf stage of maize.