EVALUATION OF SEED, STEM AND SOIL APPLICATIONS OF PROCYMIDONE TO CONTROL WHITE ROT (SCLEROTIUM-CEPIVORUM BERK) OF ONIONS

The effects of different methods of applying procymidone, either alone or combined, were evaluated for control of white rot (caused by Sclerotium cepivorum Berk.) in onions at 2 sites in Victoria. Field trials at Colac showed that seed treatments combined with sprays to the soil surface gave the most effective control of white rot, reducing disease from 78 to 16% and increasing yields from 5.7 to 14.6 t/ha in brown onions. Sprays applied to the soil surface at 2.5 kg a.i./ha had no effect on emergence and reduced disease incidence from 65.3 to 21.7%. Seed treatment at 25 g procymidone/kg seed delayed the onset of disease by 80 days and reduced disease incidence by 30%. The same treatment also reduced plant emergence by more than 27% and, therefore, did not increase yields. Dispersible granules (5 or 10%; at 2.5 kg procymidone/ha) were as effective as the soil sprays at sowing. Stem base sprays applied 11 and 19 weeks after sowing reduced disease incidence slightly but did not increase yields. Procymidone applied with bands of fertiliser 2 or 5 cm below the seed was not effective. Two formulations of procymidone, Sumisclex 500 (50% a.i.) and 275 Flocol (27.5% a.i.), were equally effective in controlling white rot. At Lang Lang, root-dips of 14-week-old seedlings in 5 g procymidone/L reduced white rot in transplanted white globe onions. Procymidone concentrations of 0.05-50 g a.i./L applied for periods ranging from 2 s to 30 min had no effect on plant establishment in a glasshouse.