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Effects of Two Foliar Pathogens on Seed Yield of Sunflower. M. L. Carson, Assistant Professor, Plant Science Department, South Dakota State University, Brookings 57007. Plant Dis. 71:549-551. Accepted for publication 13 November 1986. Copyright 1987 The American Phytopathological Society. DOI: 10.1094/PD-71-0549.

Yield reductions in sunflower resulting from leaf and stem spot caused by Alternaria zinniae and leaf spot caused by Septoria helianthi were assessed in separate experiments by inoculating plots of two sunflower genotypes (inbred line HA89A and hybrid 894) at different plant growth stages during 1981 and 1983. Seed yields of hybrid 894 were reduced 12% by S. helianthi when inoculated at the V2 growth stage in 1981 and 16% by A. zinniae when inoculated at the V6 growth stage in 1983. Seed yields, oil content, and seed weights were not consistently correlated with assessments of percent disease severity or areas under the disease progress curve. Septoria leaf spot severities were consistently greater than those caused by A. zinniae leaf and stem spot. Though capable of reducing sunflower seed yield and quality, these two pathogens do not appear as threatening as other foliar pathogens.

Keyword(s): Helianthus annuus, Septoria helianthi.