EFFECT OF AGRONOMIC TREATMENT ON YIELD, PATTERN OF SOIL WATER USE AND FOLIAR DISEASES IN WINTER WHEAT IN NORTHEAST SASKATCHEWAN
Tompkins, Darrell Keith
Three separate experiments were conducted in the period 1986 to 1988 to examine the effect of various seed rate and row spacing combinations on: yield and yield components, grain protein, soil water use and foliar disease development in winter wheat. A fourth experiment was designed to determine the optimum time to spray fungicide to control powdery mildew and septoria and to maximize grain yield. A range of disease epidemics were created by spraying with different fungicides at various stages of crop growth. The highest seed rate (140 kg ha-1) and narrowest row spacing (9 cm) considered in this study produced the highest winter wheat grain yields. Increasing the seed rate and decreasing the row spacing together produced a 21% increase in grain yield over the more conventional combination of 70 kg ha-1 seed rate and 18 cm row spacing. A higher seed rate also produced slightly earlier crop maturity. Increased nitrogen fertility, high seed rate and narrow row spacing were associated with higher levels of grain protein. Nitrogen rate, seed rate and row spacing all affected the pattern of soil moisture use. Increasing nitrogen promoted water use throughout the growing season. Increasing seed rate increased water use over the course of the growing season especially before anthesis. Narrow row spacing also increased water use over the course of the growing season. Highest grain yield and highest water use efficiency were associated with the combination of 140 kg/ha seed rate and 9 cm row spacing. Powdery mildew and septoria development were both a greater problem on the semi-dwarf cultivar Norwin than the tall cultivar Norstar. However, it was not possible to determine whether this was due to shorter plant height, a more susceptible genotype, or a combination of both factors. Powdery mildew development was promoted by increased nitrogen fertility and increased seed rate. Wide row spacing also aided powdery mildew development, particularly in the dispersal phase of its infection cycle; the effect of wide row spacing was most evident in the early stages of the epidemic. Narrow row spacing may promote powdery mildew development after the pathogen is established on a leaf. Septoria development was promoted by increased seed rate while reduced nitrogen fertility promoted septoria development under some environmental conditions. Higher wind speed within the crop canopy was associated with wide row spacing. This may be important in aiding the dispersal of powdery mildew spores and it may explain the higher levels of powdery mildew that were associated with wide row spacing in the early stages of an epidemic. The highest minimum daily relative humidity was associated with increased seed rate and reduced row spacing which may explain the higher levels of powdery mildew at the higher seed rate. Increased duration of leaf wetness was favoured by increased seed rate and to a lesser extent, by reduced row spacing. Increased duration of leaf wetness could be particularly important for septoria development, because spore germination requires the presence of water. This may account for the fact that higher levels of septoria were associated with increased seed rate. The fungicide propiconazole applied at Feekes growth stage 8 provided better disease control and produced higher grain yield and kernel weight than single applications of tridimefon or mancozeb. Split applications of fungicide provided only marginally better results than the single application at growth stage 8.