- Are the spots circular and surrounded by concentric rings?
- Yes → Go to 2
- No → Go to 5
- Do the spots have a well-defined concentric ring pattern, and thin center that may crack?
- Yes → Target spot (Well-defined concentric rings with cracked centers)
- No → Go to 3
- Do the spots expand rapidly with an irregular, water-soaked appearance?
- Yes → Erwinia leaf spot (Rapidly expanding with water-soaked margins)
- No → Go to 4
- Do the spots have irregular shapes or edges, and produce spores within the lesions?
- Yes → Brown spot (Irregular, spore-producing lesions without rapid expansion)
- No → Unknown cause (Consider further analysis)
- Do the spots have a yellow halo or appear reddish-brown around veins or stalks?
- Yes → Go to 6
- No → Go to 7
- Do the spots turn reddish-brown, and are there reddish-brown streaks or discoloration on the veins or stalks?
- Yes → Tomato spotted wilt virus (TSWV) (Reddish-brown spots with vein/stalk discoloration)
- No → Angular leaf spot (Brown, angular lesions around veins without vein discoloration)
- Do the spots appear irregular, scattered, and turn grayish-white over time?
- Yes → Weather fleck (Ozone damage) (Irregular, grayish-white spots related to ozone exposure)
- No → Go to 8
- Do the spots show localized damage such as burns or patterns typical of pesticide exposure?
- Yes → Chemical Injury (Localized burns or irregular patterns from pesticide exposure)
- No → Nutrient Deficiency or Unknown Cause (Consider further analysis)
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This dichotomous key is intended as a helpful tool to guide users in identifying potential issues and narrowing down possibilities. It is not a substitute for professional diagnosis or expert consultation. Always consult reliable resources or a qualified professional for accurate identification and management recommendations.
See here for more information on tobacco leaf spots
