Delphinium Disease Guide: Comprehensive Identification and Control

Managing Diseases in Delphinium Production

Delphiniums face a complex array of diseases including phytoplasma, bacterial, fungal, and viral pathogens. The tall, stately growth habit makes them particularly vulnerable to certain stem and crown diseases. This guide covers identification and management of the major delphinium ailments.

Aster Yellows

Phytoplasma causes leaf-like tissue in place of flower parts (green/light green), often affecting only one side of the spike. Sepals may be enlarged or dwarfed.

Management: Destroy infected plants. Control leafhoppers.

Bacterial Bud Rot, Crown Rot, and Stem Rot

Erwinia carotovora and E. chrysanthemi cause yellowing, stunting, blackened stem bases at cracks/wounds, smelly ooze in wet conditions, and stem toppling.

Management: Promptly destroy infected plants. Avoid overhead irrigation.

Bacterial Stem Rot

Pseudomonas syringae causes black, irregular leaf spots and seedling death.

Management: Destroy infected plants.

Diaporthe Blight

Diaporthe causes lower leaf browning/death during flowering, brown stem spots at soil line expanding upward, and small black pimple-like fruiting structures.

Management: Destroy infected plants. Use pathogen-free seed.

Fusarium Wilt and Canker

Fusarium oxysporum causes small brown stem spots enlarging to sunken lesions on petioles, dark brown stem cankers up to 12 inches, pink spore masses on dead canker tissue, and vascular browning in wilted plants.

Management: Destroy infected plants.

Powdery Mildew

Erysiphe polygoni produces dry, white, mealy growth on upper leaf surfaces with yellowing and death from stem base upward.

Management: Apply fungicide at first observation. Destroy plant debris at season end.

Storage Rot

Various fungi and bacteria decay tubers into soft, smelly masses.

Management: Avoid wounding when digging. Dry surfaces after soil removal before storage. Store cool and dry.

Viral Diseases

Cucumber and tobacco mosaic viruses cause conspicuous rings, line patterns, and stunting.

Management: Destroy infected plants.

Integrated Delphinium Health Program

Successful delphinium production requires: pathogen-free seed/planting material; avoidance of overhead irrigation; prompt removal of diseased plants; proper tuber handling/storage; fungicide applications for powdery mildew; vector control for virus/phytoplasma diseases; and end-of-season sanitation. The hollow stems and crown structure make delphiniums particularly susceptible to bacterial and fungal rots entering through wounds or natural openings.