Larkspur (Delphinium)
Symptom Cause  
Flowers yellow-green; deformed; spindly, leafhoppers present
Aster Yellows
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Stem at or below soil level; lesions form on infected tissue
Crown Rot
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Plant actually disappears
Deer
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Green plant colors, wilts, tans; pink mass on roots; plant dies
Fusarium Wilt
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White powder coats top of leaves
Powdery Mildew
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Leaves yellow, wilt, die
Root Rot (fungus)
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Ragged holes in leaves, often in middle
Slugs and Snails
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