Resistant cultivars, fungicides combat downy mildew of spinach

Abstract

Application of 0.5 gal/acre of Ridomil metalaxyl at planting reduced the occurrence of Peronospora effusa on spinach: 38 d after planting, treated plots averaged 9.8 diseased leaves/evaluation area, compared with 59.6 in untreated plots. At a second location, disease levels on treated plots were not significantly different to levels on untreated plots after 80 d. Foliar application of maneb 80 (2 lb/ac.), basic copper sulfate Bordeaux mixture (4 lb/ac.) or Aliette fosetyl (2, 3 and 4 lb/ac.) were evaluated. Maneb provided the best control, followed by fosetyl. Copper sulfate was least effective. Numerous commercially available and experimental lines of spinach were assessed for resistance to P. effusa; 47 d after planting, Bossanova, Bolero and RS 1250 had very low levels of disease ( 2 diseased leaves per evaluation area) compared with the Polka standard (49.3 diseased leaves). All other cultivars had disease levels comparable to, or higher than, Polka (except DMC 6, which had 33.3 diseased leaves).