When fungi or bacteria enter the roots and stems of a plant and
cause stunting, wilt and death by plugging the vascular system, this is called
a "vascular wilt." Infected plants wilt and die. If you cut into the
stem, the vascular tissues show discoloration as tan, reddish, or dark
streaking. Several fungi and bacteria may cause vascular wilts in herbaceous
Fungal wilts are caused by species of Fusarium,
Verticillium and Phytophthora. The fungus grows into the roots of a
susceptible plant, and eventually grows up into the stem. If you cut into the
stem, you can see a brown, olive green or sometimes reddish brown streaking in
the vascular tissues just under the stem epidermis.
often attacks Astilbe,
Dendranthema (garden chrysanthemum),Dicentra (bleeding-heart), Echinacea (cone flower), Lupinus (lupine), Nepeta(catnip), Ocimum (basil), and Sedum.
Verticillium wilt often attacks Aconitum (Monkshood), Dahlia, Liatris(gayfeather), Paeonia (peony), Papaver (poppy), Phlox, Rudbeckia (black-eyed-Susan), and Salvia.
Phytophthora often attacks Euphorbia (Spurge), Lavendula (lavender), Sedum, and Vinca.
Fusarium, which is usually highly host
specific, the control can be a simple rotation away from the plant that was
damaged. Verticillium has a broader host range and so
presents a more difficult problem in selecting "non-susceptible"
plants for rotation. Phytophthora is so strongly influenced by drainage
that often construction of raised beds and incorporation of organic soil
amendments to improve soil drainage will reduce disease and permit replanting
with a susceptible crop.
Bacterial wilts are much less common on herbaceous perennials
than fungal wilts.
Begonia are sometimes infected. They are
usually introduced in infected plants and can be carried in/on infected seed.
They seldom persist for longer than one growing season in soils in temperate
regions. Bacterial wilts can be diagnosed by examination of the vascular
tissues for bacterial streaming, and by isolation in culture.
The best solution for bacterial wilts is to remove infected