Abstract
Small-plot experiments for two levels of infestation (20 and 40 plants per m<sup>2</sup>) with <em>Chenopodium album</em> L. and <em>Echinochloa crus-galli</em> (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. <em>Echinochloa crus-galli</em> in the amount of 20 plants per m<sup>2</sup>, 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. <em>Chenopodium album</em> 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 m<sup>2</sup> needed to be removed no later than at the three-leaf stage of maize.
Highlights
Among all cereals, maize is the most susceptible to weed competition
Tab. 1 Influence of E. crus-galli competition on green matter yield and maize plant height depending on weed removal time
The determination of optimal time for the removal of weeds that appear along with maize emergence or those that threaten the maize crop in the second half of the growing period facilitates the decision about the application of herbicides without the risk of damaging maize plants [16,17,18]
Summary
Maize is the most susceptible to weed competition. It grows very slowly and weeds appearing in wide inter-rows strongly compete with maize for water, nutrients, and light. The efficiency of herbicides applied to regulate or control weeds depends, to a high extent, on the knowledge about time intervals in which the competitive activity of weeds in the maize field is strongest [1,2,3]. The above-mentioned knowledge is an important and strategic element in integrated weed control programs where manipulating weed populations and reduction in their number below the economic thresholds from early stages of maize development to its harvest are especially emphasized [4]. It is necessary to determine the moment by which weeds accompanying the emerged maize will not have contributed to a decrease in maize yield, the length of the required period without complete weed infestation in maize seeds sown as well as since when the growing weeds do not pose a risk to maize growth [5,6].
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