Effect of between-row and within-row spacings on development of sclerotinia wilt and yield of sunflower

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Abstract
Between-row spacing (30, 60 or 90 cm) and within-row spacing (15, 25, 36 or 47 cm) affected wilt development and yield of sunflowers growing in a field that was heavily infested with Sclerotinia sclerotiorum. Wilt incidence varied nonsignificantly and was 55.5% at crop maturity. Disease emanating from primary infection loci was common at the 15 cm spacing, and less common and delayed at the 25 cm spacing. At the 36 and 47 cm spacings, disease increase by plant-to-plant spread did not occur, and all wilt development was due to direct infection from sclerotia. Yield was highly correlated with percentage of wilted nonproductive plants (r = -0.75). Increase in between-row spacing promoted plant vigor and increased the percentage of wilted productive plants. Increase in both spacing factors decreased the percentage wilted nonproductive plants and increased yield. Yields were maximized at 26,000-49,000 plants/ha, a range of populations which had also maximized yields of sunflowers grown at other locations on soils that were noninfested. To minimize yield losses due to sclerotinia wilt, sunflowers should be planted at optimum populations, and at plant spacings (at least 36 cm) that prevent transmission of the pathogen.