5.2.6
POTENTIAL BIOHERBICIDE FOR GRASS WEEDS IN RICE IN VIETNAM

B AULD1, T NGUYEN, S HETHERINGTON1, K PHAM, T HA and C DUONG

1Orange Agricultural Institute, Orange 2800, Australia; 2National Institute of Plant Protection, Hanoi, Vietnam; 3University of Cantho, Cantho, Vietnam; 4Cuu Long Rice Research Institute, Cantho, Vietnam

Background and objectives
Grass weeds are a major problem in world agriculture because the principal food crops are members of the grass family and selective control is often difficult. In rice, several grasses are important. A project funded by the Australian Centre for International Agricultural Research was begun in 1995 to search for indigenous fungal pathogens which could have potential for development as bioherbicides for grass weeds in Vietnam.

Materials and methods
Surveys were conducted over two seasons in both the Mekong and Red River Deltas to assess the most important grass weeds and collect any fungal pathogens associated with them. Several fungal isolates were screened. Pathogenicity tests on Echinochloa spp. were conducted at three sites and a range of rice cultivars were also tested to check for selectivity.

Results and conclusions
Echinochloa crus-galli was the most important grass weed in both the Red River Delta and Mekong Delta in Vietnam. Other species of Echinochloa were also important weeds. Of many fungi tested, Exserohilum spp. appear to be the most suitable in terms of pathogenicity and selectivity in rice. Of several Exserohilum spp. compared, isolates of E. fusiforme were the most promising. Further work is in progress to confirm this and to develop methods for mass production and application of the fungus as a bioherbicide.