Eradu-patch of Lupinus angustifolius: Effects of fungicides in vitro on the causal Rhizoctonia sp. and on the root disease in the field

Abstract

Eradu-patch is a new disease of lupins caused by a thin, binucleate Rhizoctonia (TBR) and is expressed as severely stunted patches in lupin crops. A laboratory experiment to determine the toxicity of selected fungicides to the TBR found that growth was prevented by tolclofos-methyl at 5 and 10 μg mL⁻¹ and inhibited by iprodione at 10 μg mL⁻¹ but not by either furalaxyl or benomyl at concentrations up to 10 μg mL⁻¹. A selective medium for isolation of the TBR from infected root tissue was developed and tested. In the field, Eradu-patch symptoms were not evident following fumigation (methyl bromide-chloropicrin). Following a soil drench treatment with iprodione at 10 g m⁻², growth inside patches was increased but was less than one-quarter of that realised following the fumigation treatment. Soil drenches of tolclofos-methyl (1 g m⁻²), furalaxyl (1 g m⁻²) and benomyl (1 g m⁻²) did not increase the growth of lupins inside patches. Neither of the treatments that increased plant growth inside patches are commercially viable control strategies for this disease. Control strategies to be implemented by growers will need to be developed through cultural practices that may be enhanced by low cost chemical strategies.