Integrated Foliar Disease Management to Prevent Yield Loss in Argentinian Wheat Production

Published in Agron. J. 103:1441–1451 (2011) Posted online 1 Aug 2011 doi:10.2134/agronj2010.0513 Copyright © 2011 by the American Society of Agronomy, 5585 Guilford Road, Madison, WI 53711. All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. I the Rolling Pampa region of Argentina, conservation management practices such as zero tillage are increasing as alternative cropping systems. Zero tillage systems have been implemented to restore soil structure in large areas cultivated with double-crop sequences such as wheat/soybean [Glycine max (L.) Merr. ]; corn (Zea mays L.)–wheat/soybean; or wheat monoculture (Alvarez and Steinbach, 2009). Annual wheat/ soybean double-crop sequences using conventional tillage are considered less desirable because of the effect on soil organic matter and the reduced quantity of residue that soybean crops leave after harvest (Fontanetto and Vivas, 1998). In the semiarid region of Argentina, conservation management techniques are also necessary to prevent soil erosion and effectively store and use the limited amount of precipitation for crop production (Méndez and Buschiazzo, 2010). Zero tillage can also reduce costs by decreasing fuel consumption required to produce a crop (García et al., 2000). However, in the wheat/soybean system under zero tillage, as in wheat following wheat, the inoculum of necrotrophic fungi usually survives until the next wheat season; typically, a minimum of 1 to 2 yr between wheat crops is required to reduce populations of these organisms (Duczek et al., 1999). In zero tillage systems, crop residue mineralization is slow. It requires 14 to 16 mo in Brazil (Reis and Carmona, 1995), but approximately 18 to 32 mo in Argentina and Uruguay due to lower average temperatures than in Brazil (Utermark, 1995; Cordo et al., 2005). Zero tillage may have a different effect on plant diseases depending on the soil type, geographic location, environment, and the biology of the particular disease-causing organism (Krupinsky et al., 2002). Previous studies reported that tan spot [Phyrenophora tritici-repentis (Died.) Drechs, anamorph Drechslera tritici-repentis (Died.) Shoemaker] and Stagonospora blotch [Phaeosphaeria avenaria (G.F. Weber) O. Eriksson f. sp. triticea T. Johnson, anamorph Stagonospora avenae (A. B. Frank) Bissett f. sp. triticea T. Johnson] increased in zero tillage systems in wheat monoculture or wheat following fallow, although the opposite occurred when wheat followed other crops (Bailey et al., 1995, 2000; Fernandez et al., 1998, 1999; Krupinsky et al., 2007b). Conventional tillage increases crop residue decomposition, reducing fungal inoculum (Sutton and Vyn, 1990; Fernandez et al., 1998). However, others (Bailey et al., 1995; Stover et al., 1996; Fernandez et AbStrAct Zero tillage often leads to wheat (Triticum aestivum L.) yield losses from diseases caused by necrotrophic foliar pathogens. The aim of this work was to evaluate the combined effect of tillage, N fertilization, fungicides, and resistant cultivars in reducing foliar disease severity to prevent significant yield losses. A 2-yr study including combinations of (i) conventional and zero tillage; (ii) N fertilization rates 0, 80, or 160 kg ha–1 N; (iii) two fungicide treatments (with and without a fungicide (1 L of metconazole, 9%) at growth stages (GS) 32 and 39; and (iv) three wheat cultivars was conducted in the Rolling Pampas region in Argentina. The most common foliar disease in the trial was tan spot [Pyrenophora tritici-repentis (Died.) Drechs. ]. Conventional tillage reduced foliar disease severity at GS 23 by 46 and 56% and the area under disease progress curve (AUDPC) by 20 and 14% for each season, respectively compared with zero tillage. The cultivar Buck Bigua had significantly lower AUDPC values than the others. Fungicide and N application reduced disease severity at GS 23 by 35 and 34% respectively, on average over both years. Disease was less severe in zero tillage plots which received a fungicide compared to conventional tillage plots that were not treated with fungicide. In 2002 yields were greater in conventional tillage plots with 160 kg ha–1 N and fungicide application than in all other treatments. In 2003 yields were greatest in zero tillage plots with 160 kg ha–1 N and fungicide. The results of this study indicate that in spite of the increase of necrotrophic diseases, developing no-till systems in wheat monoculture is possible without significant yield losses if effective disease management practices are applied.