Influence of soil fumigation and seed tuber treatment on the control of Rhizoctonia solani on potatoes

Abstract

Five field experiments were conducted in South Australia to determine the effect of soil fumigation (metham sodium) and chemical and biological seed tuber dressing on the severity of Rhizoctonia solani on potato stems and tubers. These experiments indicated that both soil- and tuber-borne inoculum must be considered in any program aimed at controlling R. solani. Tuber treatments of either a 20 min dip in 2% formaldehyde, sprays with pencycuron (0.15 mL a.i./10 kg seed), iprodione (2 mL a.i.110 kg seed) or a spore suspension of lo6 spores/ml of Verticillium biguttatum or a dust with tolclofos methyl (4 g a.i.110 kg seed) were most effective if planted in soil fumigated with 500 L/ha metham sodium or soil with low levels of R. solani. A commercial formulation of Trichoderma harziannum and T. koningii applied as a dust at 1.3 g110 kg seed was in most cases ineffective when treated seed was planted into either fumigated or unfumigated soil. The incidence of progeny tubers with sclerotia varied between sites and ranged from 85% in an unfumigated soil planted with infected tubers to 2% in a fumigated soil planted with pencycuron-treated tubers. Except for 1 experiment where tubers were harvested early, neither seed treatments nor fumigation improved total nor marketable yield.