Laboratory and pot experiments were conducted at the Department of Weed Science, The University of Agriculture
Peshawar, Pakistan during fall 2011 and repeated in 2012. Allelopathic plants were used against wheat and associated
weeds. Allelopathic plants showed significant activity against three selected species - Triticum aestivum, Avena fatua
and Rumex crispus. Aqueous extracts of Parthenium hysterophorus and Datura alba showed significant effect against
weeds of Triticum aestivum although aqueous extract of Phragmites australis possessed moderate activity. It was noted
that aqueous extract of Oryza sativa and control were comparable for all parameters studied. Aqueous extract of P.
hysterophorus and D. alba decreased seed germination, shoot length, fresh and dry biomass as compared to the rest
of the treatments. The degree of toxicity of different treatments can be placed in the following order of inhibition: P.
hysterophorus > D. alba > P. australis > O. sativa ≥ control. The present studies showed that the plants used contain water
soluble allelochemicals that retard or inhibit the germination, growth and biomass of other species. These experiments
suggests that P. hysterophorus, D. alba and P. australis extracts may have negative effect on major weeds like A. fatua
and R. crispus. Thus there is a possibility of using these plant extracts for weed management. However, more extensive
studies is required to identify the allelopathins responsible for inhibitory effects on seed germination and plant growth.