Vlijanie na herbitsidite vrz kompetitsiskite odnosi megu kremedot (Allium cepa L.) i plevelite.

The weed vegetation at Ovce Polje (SR Macedonia) is found to consist of 34 species and the average weediness in 157.5 plants per sq m. The dominant species are:Polygonum convolvulus, Chenopodium album, Amaranthus blitoides and Amaranthus retroflexus. The characteristic population has about 10, mostly annual, species. Terrestrial plants represented by 27 species, or 79.41%, have the dominant place in the biological spectrum. The late-spring terrestrial plants are the most numerous(51.85%). Winter species are very frequent (25.93%). Regarding the biological spectrum, this weed egetation is not typical of weed associations of row crops, crops in thick crop density and winter crops. Moreover, the weed association in onion is a transition between the weed association of row crops and those of winter crops. Efficiency coefficient in annual weeds control varies, depending on the weed species, herbicide and application time and way. The crop can be kept pure until the end of vegetation with 2-times treatment. Efficiency coefficient of herbicides in 2-times impact is 98.9-99.8,depending on the means applied. Selectivity of some investigated herbicides in direct sowing and seed onion sowing was found. If, by 2-times treatment, we succeed in killing weed vegetation,i.e. reduce its competitive impact to the lowest degree possible, the yield is equal with the control. In all years of investigation there were correlations between the weed biomass and the yield of onion from seed onion. It was very strong on the average(-0.78). Almost no difference was found comparing the hoed variants with the weeded ones,i.e. the main target of hoeing was weed elimination. The investigated herbicides do not influence negatively the chemical composition of onion from seed onion. Even when there are some differences in the chemical composition, they are not statisticlly proved. The investigated herbicide residues found after the onion vegetation do not negatively affect the great number of crops to be planted after onion. Care should perhaps be taken if alfalfa, sugar beet or another susceptible crop is planned.