Crop loss from soil-borne pathogens in white clover stands assessed by chemical treatments

The effect of chemical treatments (targeting soil-borne pathogens) on biomass and botanical composition (white clover and companion grass) was measured in two series of field experiments. In one series, a mixture of fungicides was applied to an established crop stand; in the other series, the biocide dazomet (40 g m(-z)) was incorporated into the soil before sowing a mixture of white clover and grass. Fungicidal application significantly improved yields of white clover for all harvests (> 200 %), but did not affect grass yields. The dazomet treatment hampered white clover yields the first year, but yields increased the second year and were > 40 % higher relative to controls. In addition, in the dazomet-treated plots, plants were healthier, based on disease readings of roots; and during the second year (in one of two experiments), grass yields were also significantly higher due to dazomet treatment. In a greenhouse testing of Fusarium culmorum and F. avenaceum isolates (from white and red-clover roots) for pathogenicity, shoot dry weight of timothy and meadow fescue were affected following inoculation, indicating that these clover and grass species have pathogens in common.