The herbicidal potential of tagetes minuta and tagetes patula extracts and their residues on the germination and growth of some crop plants.
The study was conducted to determine the herbicidal effect of Tagetes patula and Tagetes minuta on the germination and seedling growth of Eleusine coracana, Rorripa indica, Capsicumfrutescens and Phaseolus vulgaris. Seeds of T patula and T minuta were planted on two plots and the seedlings harvested after attaining the height of7-1O ems. Extracts of water, methanol and thiophenes were obtained from the roots and leaves of the dried samples of T minuta and T patula. Test plant seeds of Eleusine coracana, Rorripa indica, Capsicumfrutescens and Phaseolus vulgaris were subjected to three levels of extract concentration; 20%, 40% and 60% in a completely randomized block design with each replicated three times. The biological activities of these extracts were assessed by examining the reduction in mean germination percentage and the subsequent delay of germination time. Root length, shoot and leaf area were measured to determine the suppression effect of Tagetes extracts on the growth of seedlings of the test plants. The SPSS package was used to analyze the data collected in which analysis of variance and post hoc test using LSD were carried out to explore the impact of each extract on the germination percentage, delay and on seedling growth. The results showed a significant decrease at p<0.05 in the mean germination percentage, germination time, root and shoot length. The magnitude of germination inhibition was shown to be proportional to the extract concentration. Germination inhibition and seedling growth suppression was great in the residue, water and methanol treatment compared to thiophene. Roots of the test plants were shown to be the most affected by the extracts, followed by the shoot length, though the leaf area was non significantly affected (p>0.05). The sensitivity to these extracts varied among the test plants with R. indica showing the lowest mean germination percentage in all treatment, however, the mean germination time depended highly on the concentration of the extract. The test plants C.frutescens, E. coracana and P. vulgaris similarlyregistered a decline in mean germination percentage and an average delay on the germination of the seeds. Therefore, the residues and the crude extracts of water and methanol did show significant reduction effect on the germination and the growth of the seedlings.