BLIGHT /
CROWN ROT
Southern Blight
(Sclerotium rolfsii)
(Photo courtesy of Missouri
Botanical Garden PlantFinder)
Southern Blight
Crown rot, sometimes called southern blight, is
caused by several soil-borne fungi, including Pellicularia rolfsii,
Sclerotium delphinii, and Sclerotium rolfsii. The fungi survive
in the soil and are spread by flowing water, transported or contaminated
soil, transplants, and tools. Blight causes deterioration and rotting of
tissues at the crown causing the leaves to turn yellow, collapse, and die. Infected
plants develop discolored, water-soaked stem lesions near the soil line. A white, cottony fungus is
visible on the surface and in the soil around the infected plant. Also,
small light brown structures that resemble mustard seeds (sclerotia) spread
over the surrounding soil. Sclerotia may be so numerous that they form a
crust on the soil. Conditions of 86–95 degrees F for several days with
intermittent rains are conducive for this fungal development.
Fungicides registered for control of crown rot
include mancozeb and thiophanate methyl (Cleary 3336). PCNB drench has also
shown success in curing blight. To help prevent blight, a granular form of
PCNB should be included in the planting medium and gardens should be
top-dressed each spring. If blight does not respond immediately to
treatment or is persistent in your garden, remove diseased plants immediately.
Excavate the surrounding soil, replacing it to a depth of 8 inches deep and
wider than the area vacated by the diseased plant. Sterilize all digging tools
with a bleach bath to reduce the chance of spreading the disease to other
locations in your garden.
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