Please check the attached information from Penn State and try to match the symptoms displayed by your plants.
Carnation (Dianthus) Diseases
Disease Symptoms Pathogen/Cause Management Alternaria Leaf Spot Small purplish spots form on leaves. Their centers become brown while the leaf yellows. Alternaria dianthicola or Alternaria dianthi
Apply a fungicide to protect healthy plants. Bacterial Slow Wilt or Stunt Wilting, twisting, curling and stunting of lower leaves and side shoots followed by death of lower leaves. Wilted plants may recover only to wilt again. Stunted plants have narrow, yellow-green leaves. Symptoms require several weeks to develop. Erwinia chrysanthemi
Grow in raised beds pasteurized between crops. Use culture indexed cuttings free of the pathogen. Destroy infected plants. Bacterial Wilt Leaves turn gray-green then yellow and die. Roots rot. Vascular tissue browns.Cracks develop in internode tissue. Slime oozes from these cracks when humidity is high. Pseudomonas caryophylli
Pot and propagate in pasteurized raised beds. Use clean, disinfested tools. Use culture-indexed cuttings free of the pathogen. Destroy infected plants. Botrytis Blight Petals turn brown and are covered with gray, fungal growth. Botrytis cinerea
Space plants to insure good air circulation. Maintain low humidity. Avoid watering late in the day. Remove crop debris. Apply a fungicide to protect healthy plants. Fusarium Wilt Lower leaves yellow and wilt up one side of plant. Symptoms progress up plant. Top of main shoot grows at right angle to main stem. Late in the disease, root and stems rot. Fusarium oxysporum
Pot and propagate in pasteurized raised benches. Use culture indexed plants free of the pathogen. Fusarium Stem Rot Reddish-brown spots at the base. No vascular discoloration occurs beyond the rotted area. Fusarium graminearum, F. avenaceum, or F. culmorum
Plant only healthy, pathogen-free cuttings in pasteurized, raised beds. Greasy Blotch Small, web-like patterns give leaves a greasy appearance. Leaves yellow and die. Zygophiala jamaicensis
Maintain relative humidity below 85%. Phialophora Wilt Plants wilt, leaves yellow, and vascular tissue is discolored dark brown. Phialophora cinerescens
See Fusarium wilt above. Rhizoctonia Stem Rot Stems at the soil level have a lesion with a brown border. Stems have dry shredded appearance. Rhizoctonia solani
Plant in pasteurized, raised beds. Apply a soil drench to protect healthy plants. Rust Small blisters containing rust-red spores form on leaves. Uromyces dianthi
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 or have flower color breaking. 15 different viruses are known. Plant virus-indexed cuttings. Maintain good insect and mite control. Destroy infected plants.