Fungicide seed treatments increase growth of perennial ryegrass

Field, laboratory and glasshouse experiments were carried out to measure effects of seed treatments with captan or thiram on growth of perennial ryegrass (Lolium perenne L.). Field-sown captan- or thiram-treated seed gave twice as many seedlings as untreated seed. Spaced plants growing from fungicide-treated seed produced almost 6 times more dry matter 16 weeks after sowing than those from untreated seed. This effect, though diminishing with time, was still apparent more than a year after sowing. Fungicides in sterile agar growth medium were phytotoxic to seedlings at concentrations of 10μg/ml and greater. Seedlings grown from treated seeds sown from 5 to 15 mm away from developing colonies of the virulent seedling pathogenFusarium oxysporum Schlecht. were more than 4 times larger than those grown from untreated seeds. Captan-treated seed sown into pots containing field soil produced more and larger seedlings than untreated seed. Methyl bromide fumigation of the same soil also increased both number and size of seedlings. Fungicidal, rather than direct chemical effects, at early stages of seedling growth, account for increased growth of plants from fungicide-treated seed.