<![CDATA[Early and accurate field identification of tomato diseases is critical for timely intervention, yet farmers in resource-limited settings frequently lack access to expert diagnosis. This paper proposes a lightweight, knowledge-based decision support system (DSS) for differentiating nine economically important tomato diseases and pests using a recently published tabular knowledge base. The DSS operates in two stages: first, it represents each disease's symptom description as a TF-IDF vector (unigram and bigram, lemmatized, with domain-specific stopword filtering) and retrieves the best-matching disease via cosine similarity to an observed symptom query; second, it refines the ranking using a rule-based environmental condition filter (warm-humid or cool-wet) when field context is available. We evaluate the framework on 121 individual symptom sentences extracted from the knowledge base as independent field-observation queries. The symptom-similarity stage alone achieves a sentence-level top-1 retrieval accuracy of 99.2% (120/121 sentences), with only one Mosaic Virus sentence – the non-specific phrase ‘stunted growth and reduced yields’ – initially misranked. Symptom cosine similarity analysis reveals that Target Spot is the most structurally confusable disease, sharing the highest off-diagonal similarity with Early Blight (0.144), Late Blight (0.137), and Septoria (0.131). Treatment complexity analysis further shows a clinically important distinction between fungal/pest diseases (20 or more chemical treatment options each) and viral diseases (Mosaic Virus: 2; Yellow Leaf Curl Virus: 1), where chemical interventions are ineffective and prevention-only strategies are documented.]]>
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