3.1.4: Fungal diseases
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Not started yet — this one needs some love.
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Rose black spot is caused by a fungus and affects rose plants.
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Symptoms: purple or black spots on leaves; leaves turn yellow (chlorosis) and drop early.
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Effect on plant: less healthy leaf area and less chlorophyll reduce photosynthesis, so less glucose is made for growth.
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Spread: spores are carried by water or wind.
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Control: use fungicides and/or remove and destroy affected leaves to reduce spread.
Common exam mistakes
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Rose black spot is caused by a fungus — not a virus or bacterium.
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It is spread by water or wind — not exclusively by direct contact.
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Leaves turn yellow because photosynthesis is reduced — the mechanism is reduced chlorophyll/leaf loss.