Allelopathic Potential of Bermudagrass and Johnsongrass and Their Interference with Cotton and Corn

Field experiments were conducted in northern Greece during the 2002 and 2003 growing seasons to study interference between bermudagrass [Cynodon dactylon (L.) Pers] or johnsongrass [Sorghum halepense (L.) Pers] and cotton (Gossypium hirsutum L.) or corn (Zea mays L.). Moreover, bioassay studies were also conducted to assess allelopathic potential of these two weeds on cotton and corn as well as on barnyardgrass [Echinochloa crus-galli (L.) P. Beauv.] and bristly foxtail [Setaria verticillata (L.) P. Beauv.]. The bioassay experiments showed that cotton, barnyardgrass, and bristly foxtail germination, total fresh weight, and root length were inhibited by bermudagrass or johnsongrass extracts more than those of corn. In addition, johnsongrass extracts caused greater germination, fresh weight, and root length inhibition than bermudagrass extracts. In the field, growth and yield of cotton were reduced due to bermudagrass (200 and 400 stems m-2 from planted rhizomes) or johnsongrass (100 and 200 stems m-2 from planted rhizomes) season-long interference 50 and 74% or 64 and 86%, respectively, averaged over the two weed densities. The corresponding corn losses were 46 and 30% or 62 and 41%, respectively. Both stem number and fresh weight of bermudagrass or johnsongrass increased with increasing interference duration, and they were greater where both weeds were grown with cotton than with corn. These results suggest that there is growth inhibition of both crops due to potential allelopathic substances released from the two perennial weeds, but cotton growth was inhibited more than corn. Furthermore, cotton and corn yield were reduced more by the johnsongrass interference compared with that caused by bermudagrass.