Post-dispersal predation of weed seeds in rice fields

P>Post-dispersal weed seed predation can cause a substantial reduction in the number of weed seeds entering the seed bank and, as a consequence, reduce the number of weeds growing in subsequent seasons. Investigations on seed predation on four tropical rice fields in the Philippines were conducted to determine (i) the magnitude of post-dispersal seed predation after rice harvest, (ii) whether vertebrates or invertebrates are the main seed predators, (iii) whether seed predation is affected by crop residue, (iv) whether seed predation is affected by proximity to the field edge, and (v) whether predation differs among seeds of the grasses Digitaria ciliaris, Echinochloa colona and Eleusine indica. Seed removal rate over a 14-day period ranged from 78% to 91% among fields, was slightly higher in the interior of the fields (89%) than in the field margins (85%) and slightly higher without residue cover (89%) than with (86%). Selective exclosures indicated that invertebrates, presumed to be mainly fire ants (Solenopsis geminata), were the main seed predators (96%) and vertebrates, presumed to be mainly rodents, secondary predators (38%). Seed removal of D. ciliaris was higher (93%) than of E. indica (88%) and E. colona (75%). Results suggest substantial seed predation could contribute to ecologically-based weed management in rice. Further studies are required to determine season-long seed predation rates and to confirm the identity of the predators involved. Ways to integrate these seed predators into prevailing cropping practices need to be developed.