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

Field experiments at 7 sites over 3 seasons showed that the dicarboximide f ungicides iprodione and procymidone could reduce brown spot severity in lup in 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 slight ly or no improved disease control. Where either brown spot or pleiochaeta r oot rot was severe, seedling death occurred and seed treatment increased pl ant population, dry matter and grain yield. In some experiments seed treatm ent reduced pleiochaeta root rot. In no experiment was there an additional grain yield benefit from applying either fungicide above 0.12 g/kg seed eve n 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. Di sease reduction can be measured higher up the plant later in the season as a result of reduced secondary infection.