INFLUENCE OF AGRONOMIC PRACTICES ON CANOPY MICROCLIMATE AND SEPTORIA DEVELOPMENT IN NO-TILL WINTER-WHEAT PRODUCED IN THE PARKLAND REGION OF SASKATCHEWAN

In areas with favourable growing conditions, high seeding rates (SRs), narrow row spacings (RSs) and nitrogen fertilization (N) are required before high yield potentials of winter wheat (Triticum aestivum L.) are realized. Changes in these variables produce changes in crop-canopy microclimate that may influence the development of foliar pathogens. This study examined the relative differences in crop-canopy microclimates due to different RS and SR combinations and determined the effect of SR, RS and N fertility on septoria (Septoria nodorum Berk. and Septoria tritici Rob. ex Desm.) development on normal height and semi-dwarf cultivars grown under no-till in the Parkland region of Saskatchewan. The daily mean value for solar radiation penetrating to the base of the crop canopy was 1100 mumol m-2 s-1 for 36-cm RS. This was 30% higher than the 845 mumol m-2 s-1 observed for 9-cm RS. The increased light interception by the canopy was associated with higher dry matter production and grain yield. During peak periods, wind speed was 56% higher within the 36-cm RS canopy than within the 9-cm RS canopy. Increased duration of leaf wetness was associated with 9-cm RS and 140-kg-ha-1 SR treatment. Cooler air temperature and higher RH within the canopy occurred for the 9-cm RS - 140-kg-ha-1 SR treatment. Differences in air temperature and RH between the 9-cm RS - 140-kg-ha-1 SR and the 36-cm RS - 35-kg-ha-1 SR treatments were smaller at night and greater during the day. The maximum differences occurred at mid-morning and mid-afternoon, when the 9-cm RS - 140-kg-ha-1 SR canopy was 1.5-degrees-C cooler and had a 4.5% higher RH than the 36-cm RS - 35-kg-ha-1 SR canopy. Septoria severity increased when SR increased from 35 kg ha-1 to 140 kg ha-1. Septoria severity was not influenced by RS. Septoria severity was greater on the flag leaf of the semi-dwarf cultivar Norwin than on die tall cultivar Norstar. Increased N fertility reduced septoria severity in one trial. These observations demonstrated that, in addition to the influence on yield potential, high SR and narrow RS produce a canopy microclimate that is favourable for the development of septoria.