| Crown rot, sometimes called southern blight or
southern stem rot, is caused by several soil-borne
fungi. It affects herbaceous plants and some woody
plants but is most commonly found on ajuga,
anemone, campanula, chrysanthemum, delphinium,
hosta, hydrangea, iris, narcissus, phlox, rudbeckia,
scabiosa, sedum, and tulip. The problem generally
requires removal of the diseased plant.
Symptoms and Diagnosis
Crown rot causes deterioration and rotting of the
tissues at the crown of the plant causing the leaves
to turn yellow, collapse, and die. When the
temperature exceeds 70 degrees F, infected plants
develop discolored, water-soaked stem lesions near
the soil line. During periods of high humidity, coarse
cottony webbing (mycelium) develops and fans out
over the stem base and surrounding soil. Sclerotia,
which resemble mustard seeds and vary from white
to reddish tan to light brown in color, develop at the
base of the plant. Enough sclerotia may form to
create a crust on the soil.
Life Cycle
The fungi which cause crown rot (Pellicularia rolfsii,
Sclerotium delphinii, and Sclerotium rolfsii) survive
in the soil and are spread by flowing water,
transported or contaminated soil, transplants, and
tools. Conditions of 86–95 degrees F for several days
with intermittent rains are conducive for
fungal development.
Integrated Pest Management Strategies
1. Remove diseased plants as soon as they are
noticed. Plants can be buried, but do NOT place
them in your compost pile.
2. Excavate surrounding soil. Dig out and replace
the soil to a depth of 8 inches and 6 inches
beyond the diseased area.
3. Solarize the soil. If you do not remove the soil
and the area receives at least two to three hours
of direct sun, solarize it. Cover the area with clear
plastic and leave it for two to three months in the
heat of the summer.
4. Provide better drainage. Increasing the organic
content of the soil and improving drainage will
make the environment less desirable to
the fungus.
5. Sterilize all tools. Clean all tools used in digging
with a solution of 1–part bleach to 9–parts water
to disinfect the tools and reduce spreading the
disease to other locations in your garden.
6. Try fungicides. Pesticides registered for control of
crown rot include mancozeb and thiophanate
methyl (Cleary 3336). |
