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Yield Loss by Brassica campestris and B. napus from Systemic Stem Infection by Albugo cruciferarum. F. R. Harper, Research Station, Canada Department of Agriculture, Lethbridge, Alberta T1J 4B1; U. J. Pittman, Research Station, Canada Department of Agriculture, Lethbridge, Alberta T1J 4B1. Phytopathology 64:408-410. Accepted for publication 15 October 1973. DOI: 10.1094/Phyto-64-408.

In a field experiment with crops sown at different dates, the relationship between yield of Brassica campestris ‘Span’ and severity of the systemic stem infection phase of white rust (staghead) caused by Albugo cruciferarum was expressed by the equation Y = 100 – 0.952X, where Y was yield expressed as percent of potential and X was percent of stems systemically infected. The equation Yield loss (%) = 100 × Number of stems systemically infected Total number of stems examined is suggested for use in disease loss assessment. Brassica napus ‘Oro’ showed no symptoms of infection by the biotype of A. cruciferarum that attacked Span.