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<i>Alternaria dauci</i> is the causal agent of <i>Alternaria</i> leaf blight (ALB) in carrot (<i>Daucus carota</i>) crops around the world. However, to date, <i>A. dauci</i> has received limited attention in its production of phytotoxic metabolites. In this investigation, the bioassay-guided isolation of the extract from liquid cultures of <i>A. dauci</i> resulted in the isolation of two metabolites identified as <i>α</i>-acetylorcinol (<b>1</b>) and <i>p</i>-hydroxybenzoic acid (<b>2</b>), based on their spectroscopic data and results from chemical correlation reactions. Testing of both metabolites in different assays showed an important phytotoxic activity for <i>p</i>-hydroxybenzoic acid (<b>2</b>) when tested in the leaf-spot assay on parsley (<i>Petroselinum crispum</i>), in the leaf infiltration assay on tobacco (<i>Nicotiana alata</i>) and marigold (<i>Tagetes erecta</i>), and in the immersion assay on parsley and parsnip (<i>Pastinaca sativa</i>) leaves. Quantification of the two metabolites in the crude extract of <i>A. dauci</i> kept at different times showed that <i>p</i>-hydroxybenzoic acid (<b>2</b>) is one of the first metabolites to be synthesized by the pathogen, suggesting that this salicylic acid derivative could play an important role in the pathogenicity of the fungus.