One significant biotic barrier to crop production is weeds. The present study aims to analyze the weed vegetation associated with cultivated crops in the newly reclaimed lands in the three Suez Canal governorates (Ismailia, Suez and Port-Said). A total of 148 weed species (96 annuals and 52 perennials) belonging to 110 genera and 26 families were recorded. The most species-rich families were Poaceae, Asteraceae, Amaranthaceae and Fabaceae. Therophytes and Chamaephytes were the most prevailing lifeforms. The chorological analysis of the vegetation revealed that Cosmopolitan, Saharo-Sindian and Mediterranean chorotypes either pure or extended into other regions form the major component of the floristic structure. The application of TWINSPAN classification technique yielded four vegetation groups. These groups were dominated by Schismus barbatus, Senecio glaucus, Cynodon dactylon and Melilotus indicus. Biodiversity indices (species richness, Shannon's index, Simpson's index and Evenness index) indicated that vegetation group B was the most diversified among other groups. The ordination of stands in the study area by using DECORANA program showed that the vegetation groups obtained by TWINSAPAN are distinguishable and have a clear-cut pattern of segregation on the ordination diagrams.Canonical Correspondence Analysis (CCA) indicated that soil texture, total nitrogen, calcium, magnesium, potassium, sulphates, electrical conductivity and organic matter were the main soil parameters which determined the distribution of weed vegetation in the study area.

The present study was conducted to determine the allelopathic effect of the aqueous extracts of Cynanchum acutum, Anagallis arvensis, Chenopodium murale, Malva parviflora, Sonchus oleraceus and Portulaca oleracea on the germination and growth of Bidens pilosa plant. Also, the presence of total phenols, flavonoids, saponins, tannins and alkaloids, were screened in the studied plants. The results indicated that the aqueous extract of C. acutum, A. arvensis, C. murale, M. parviflora, S. oleraceus and P. oleracea showed a remarkable allelopathic effect on germination and growth of B. pilosa. The effectiveness of the extract was much higher on C. acutum, as it is the most effective in reducing the shoot and root growth of B. pilosa followed by S. oleraceus, M. parviflora, P. oleracea, C. murale and A. arvensis. The allelochemicals such as total phenols, flavonoids, saponins, tannins and alkaloids present in C. acutum, A. arvensis, C. murale, M. parviflora, S. oleraceus and P. oleracea. From the present study, it is concluded that the aqueous extract of the tested plants can be used as natural source in controlling B. pilosa.