|Alternaria Leaf Spot||Dark brown to black spots form on leaves. These enlarge to engulf large portions of the leaf. Spots on petioles may allow them to break.||Alternaria sensecionis||Remove infected leaves. Water in a manner that keeps leaf surfaces dry. Maintain low humidity. Apply a fungicide to protect healthy plants.|
|Downy Mildew||Yellow spots on leaves become black. Sparse fungal growth may appear on the underside of infected leaves.||Plasmopara halstedii||Water in a manner that keeps leaf surfaces dry. Remove infected leaves.|
|Phytophthora Root and Collar Rot||Roots and stem at the soil line rot. Plants wilt and die.||Phytophthora cinnamomi, P. cryptogea, P. megasperma, and P. drechsleri||Plant in pasteurized potting mix. Apply a fungicide to protect healthy plants.|
|Powdery Mildew||White fungal growth forms on the leaf surface.||Golovinomyces cichoracearum (formerly Erysiphe) or Sphaerotheca fusca||Heat and ventilate to maintain low humidity at night. Apply a fungicide to protect healthy plants.|
|Viruses||Leaves may be mottled, have yellow spotting, dead flecks, line or ring spot patterns. Plant may be distorted, have flower color breaking, or may be stunted. Veins may be killed along with petioles and the entire plant.||Impatiens necrotic spot, streak and mosaic viruses.||Destroy infected plants. Maintain good thrips and mite control.|
Impatiens necrotic spot virus infection symptoms on leaves and stem.
Prepared by Gary W. Moorman, Professor of Plant Pathology
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