Allelopathic activity of leaching from dry leaves and exudate from roots of ground cover plants assayed on agar

The effects of leaches from dry leaves of 71 ground cover plant species on lettuce were tested at the first screening. The inhibitory effects on radicle and hypocotyl elongations of lettuce varied with the different species of cover plants that were used. Eight species of Oxalis showed strong inhibitions (4–27% of untreated control on radicle elongation). Inhibitory activities of seven species of cover plants on three weed species, live amaranth (Amaranthus lividus), southern crabgrass (Digitaria ciliaris) and common lambsquarters (Chenopodium album), were tested at the second screening. Moss pink (Phlox subulata), trefoil (Oxalis brasiliensis), red spiderlily (Lycoris radiata), creeping thyme (Thymus serpyllum), European pennyroyal (Mentha pulegium), roman chamomile (Chamaemelum nobile) and star-of-Bethlehem (Ornithogalum umbellatum) were selected as donor plants because of their high inhibitory effects on lettuce growth and their usefulness as ornamental ground cover plants. Effects of leaches from dry leaves and exudates from the roots of these species were assayed on agar. Radicle elongations of all tested weed species were inhibited by leaches from trefoil and red spiderlily (8–31% and 14–24% of untreated control, respectively) and exudates from moss pink, trefoil and creeping thyme (11–43%, 31–74% and 22–67% of untreated control, respectively).