A range of fungicides was tested against rust (Uromyces lupinicolus) and brown spot (Pleiochaeta setosa) on autumn-sown white lupin (Lupinus albus) in three experiments in harvest years 1995, 1997 and 1998. Rust was severe in all three years but did not develop in an additional experiment in 1996. Brown spot occurred only in 1997 and 1998 when natural inoculum was augmented by an artificial source and weather conditions were favourable for inoculum dispersal and disease development. Tebuconazole was the only fungicide tested that controlled rust consistently, whereas iprodione+thiophanate-methyl, tebuconazole and prochloraz each decreased the severity of brown spot. Yield increases in 1997 and 1998 were thought to be attributable mainly to control of rust. Fungicides were most effective when applied as soon as symptoms were observed. Two applications of an effective fungicide generally controlled disease more than a single application; a third application gave no additional benefit.

Summary.Experiments in controlled environments tested interactions between freezing soil (a compost‐vermiculite mixture) and below‐ground infection of white lupins with each of three pathogenic fungi (Botrytis cinerea, Fusarium avenaceum or Pleiochaeta setosa) on plant disease and death. Whilst soil freezing (up to 4 days at – 1oC) caused slight necrosis and increased the severity of disease symptoms, incidence of plant death was increased only after inoculation, before freezing, of the lower hypocotyl of the youngest plants (soil frozen at less than 17 days old) with P. setosa. It is concluded that the contribution of below‐ground infection by pathogenic fungi to overwinter losses in autumn‐sown white lupin crops is exacerbated to a negligible extent by soil freezing, the main primary cause of such losses.