Management practices to reduce gray leaf spot of maize

The beneficial effects of stubble tillage on soil and water conservation are widely recognized, but surface stubble also increases the potential for crop damage by fungal pathogens that overwinter in the previous season's debris. In recent years, gray leaf spot (GLS) has become a major yield-limiting disease, resulting in grain yield losses as high as 60% in high yield potential maize (Zea mays L.) production areas. A study was launched to investigate strategies that could he adopted to facilitate the continuation of conservation tillage practices without exposing maize to unnecessarily high risk from GLS. The aim or the study was to investigate the interactive effects of four tillage practices leaving varying amounts of surface residues and fungicide treatments for the control of stubble-associated pathogens. In the hot, dry season, unfavorable for GLS, the onset of disease was 23 d earlier in no-till with higher disease than conventional tillage. The benefits of conserved soil moisture under stubble tillage with concomitant higher grain yields than conventional tillage offset the detrimental effects of higher disease. Results from the study indicate that tillage practices are unlikely to have a major impact in managing GLS; since the mean yield of conventional tillage with minimal stubble (3% residue), during four seasons, was between 28 and 209 kg ha-1 lower than tillage treatments leaving 82 and 26% stubble on the soil surface, respectively. During the four seasons of the study, grain yield responses to fungicide treatment ranged from 477 kg ha-1 in unfavorable seasons to 3830 kg ha-1 in seasons favorable for GLS. The judicious application of fungicides will reduce the risk of financial loss from GLS and will allow the continuation of the desirable stubble tillage practice in sustainable farming systems