Natural chemical substances as phenolic compounds, alkaloids, falvoniods, tannins, coumarins, terpenes, quinones, glycosides, cyanates etc., are found in different crop plants as sorghum, sunflower, brassica, eucalyptus, sesame and tobacco. The number and quantity of these chemicals vary. Some plant species contain more allelochemicals as in sorghum, while some chemicals may be highly effective such as sorgoleone, wherein others may have few.
These chemicals are produced in all plant parts, seed, grain, roots and leaves. The quantity, number and concentration may change at different stages of growth. Generally their concentration is high in seed and seedling stages which may decrease during active growth and again increases at maturity. These chemicals (Allelochemicals) are water soluble and can easily be extracted. The donor plants which release these chemicals generally store them in the cell in a bound form of water soluble compound. It has been suggested that upon cleavage by plant enzyme or environmental stress, the phytotoxic chemicals are released in the environment.
The allelochemicals obtained from different plants when used collectively show cumulative synergistic or antagonistic effects. These may also be combined with lower doses of herbicides leading to reduced costs and improved environmental safety.
Keeping in view the herbicidal role of these natural plant products, studies were conducted at the Weed Science Allelopathy Laboratory, Department of Agronomy, University of Agriculture, Faisalabad.
In this study water extract of Sorghum (Sorghum bicolor L.) was combined in different proportions with water extracts of other allelopathic plants i.e., eucalyptus, sesame, sunflower, tobacco and brassica to explore the feasibility of controlling wheat weeds. Combined effects of sorghum water extract (sorgaab) with reduced doses of synthetic organic compounds (herbicides) such as 2, 4-D, benzoic acid, sulfosulfuron and isoproturon were also investigated.
Interesting and encouraging results were achieved which clearly indicated that allelopathic water extract of sorghum (sorgaab), sunflower, eucalyptus, brassica, sesame and tobacco as foliar sprays at 20 and 40 days after sowing on wheat crop, inhibited the growth and biomass of common wheat weeds species as Avena fatua, Phalaris minor, Chenopodium album, Anagallis arvensis, Medicago polymorpha, Rumex dentatus and Fumaria indica by 26-47 per cent, 43-62 per cent, 18-37 per cent, 28-32 per cent, 19-33 per cent and 17-27 per cent, respectively.
It was also determined that the allelopathic sorghum water extract (Sorgaab) can be used as tank mixture to reduce the doses of synthetic herbicides isoproturon by 40-55 per cent, sulfosulfuron by 57 per cent, 2, 4-D by 67 per cent and benzoic acid by 60 per cent.
The findings of these studies suggest that allelopathic crop extracts with other organic compounds or with lower herbicide doses is very effective in controlling the wheat weeds by 57-98 per cent and improving the wheat yields by 82-93 per cent. This study is of great significance for farmers as this reduces their production costs and helps to promote environment safety, enhance natural resource utilization for sustainable and quality food grain production in the country.