Low rates of dicarboximide seed treatment reduce brown spot in narrow-leafed lupin

Abstract

Field experiments at 7 sites over 3 seasons showed that the dicarboximide fungicides iprodione and procymidone could reduce brown spot severity in lupin seedlings when applied as a seed treatment at rates as low as 0.06 g/kg seed. Treatment at previously recommended rates (1.0 g/kg) gave only slightly or no improved disease control. Where either brown spot or pleiochaeta root rot was severe, seedling death occurred and seed treatment increased plant population, dry matter and grain yield. In some experiments seed treatment reduced pleiochaeta root rot. In no experiment was there an additional grain yield benefit from applying either fungicide above 0.12 g/kg seed even where disease pressure was extreme at an artificially infected site. The direct effect of dicarboximide seed treatment appears mainly due to reduced infection on cotyledons and to a lesser extent the first 4 true leaves. Disease reduction can be measured higher up the plant later in the season as a result of reduced secondary infection.