Studies on the etiology of black rot, Stemphylium radicinum (Meier, Drechsl. & Eddy) Neerg., and leaf blight, Alternaria dauci (Kühn) Groves & Skolko, on carrot crops; and on fungicide control of their seed‐borne infection phases

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Abstract
SUMMARY: Of nineteen commercial samples of carrot seed in use at Wellesbourne in 1963, eight were found to be infected with both Stemphylium radicinum and Alternaria dauci and five with S. radicinum alone. Both fungi caused damping‐off of seedlings and when carrots were grown at high densities A. dauci caused severe foliar infection. Neither fungus gave rise to marked infection of ware crops at normal spacings but, when seed infected with S. radicinum was sown in the autumn, the resulting seed crop was heavily infected by the succeeding autumn.Spring‐sown carrots grown in soil that had borne infected crops or contained debris infected with either fungus showed little or no infection in the autumn or after storage for 3 1/2 months; autumn‐sown or spring‐planted (steckling) carrots put into ground infected with S. radicinum showed severe infection in the following autumn. This suggested that ware‐crop carrots were resistant to infection from the soil whereas the seed crop was not.Both fungi were eradicated from seed by a 24 hr. soak at 30d̀ C. in a 0.2% thiram suspension, but were not completely eliminated by seed dust treatments with a range of fungicides.

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