Pathogen: Verticillium alboatrum and Verticillium dahlia.
Hosts include: Aconitum, Aster, Chrysanthemum, Coreopsis, Dahlia, Delphinium, Dianthus, Helichrysum, Papaver, Paeonia and Phlox.
Symptoms: Wilting and dieback, stunted growth and yellowing, sometimes affecting only part of the plant. Some plants may have discoloration or streaking in the vascular system.
Spread: Verticillium is common in soil, where it survives as mycelium. Verticillium dahlia can also produce microsclerotia, a long-term survival structure. Plants are infected through roots, and infection moves into the vascular system. Wood chips produced from infested trees and used in potting media or as mulch can spread the disease. Disease incidence is less common in plants grown in soilless potting media.
Management: Remove all symptomatic plants; fungicide treatments are generally not helpful. Avoid planting susceptible plants in fields with high populations of Verticillium. Feeding by root and lesion nematodes can increase damage from Verticillium wilt. Plants and soil can be tested for nematodes and the populations quantified by submitting samples to a diagnostic lab. Maintain good control of weed hosts in the field – some weeds are hosts for Verticillium.