There
are several different organisms that may be involved
in rot diseases of daylilies,
such as species of the fungi Fusarium, Phytophthora,
Rhizoctonia, Pythium and Sclerotium as well as bacterial
soft rot caused by Erwinia. In 2004, a fungus generally
associated with woody plants was identified in diseased
daylilies for the first time. Armillaria mellea infection
is known most commonly as "Shoestring Root Rot" in
North America because of the shoestring like structures
it produces, and in some other countries it is referred
to as "Honey Fungus"
due to the color of the mushrooms.
The text
below has been kindly written for us by Dr. Guido
Schnabel of Clemson University, who made the initial
identification of this disease in daylilies. This
fungus is not likely to be a common cause of rot
disease in daylilies but could be a possibility when
gardens have been cleared from woodland, or where
there are dead or diseased trees or shrubs known
to be infected with Armillaria.
Root
rot, Armillaria root rot:
A new fungal pathogen
on dayliliesG. Schnabel,
Department of Entomology, Soils, and Plant Sciences,
Clemson University, Clemson SC 29634. Schnabe@clemson.edu.
Armillaria
root rot disease is a soil borne pathogen that
primarily affects woody plants but occasionally is
reported on herbaceous species. In June 2004, the
disease was discovered for the first time on daylilies.
The diseased plants were located in South Carolina
and grown in well drained loamy soil that is supportive
of Armillaria root rot disease. The site used to
be woodland and was just recently cleared. Daylilies
were planted around multiple hardwood stumps and
an Armillaria root rot symptomatic dogwood tree.
Symptoms
were similar to drought stress and included poor growth
of the plant and yellowing of leaves. A cross section
through the crown of wilting plants revealed necrotic
areas with fan-shaped, white fungal mat growing inside.
In some instances, mycelial fans were also discovered
in primary roots. Black shoestring like rhizomorphs
were found on and near the daylily and dogwood roots
and in other places of the yard. These rhizomorphs
are produced by the fungus to explore the area and
look for new prey. They are initiated on a food base,
such as tree stumps.
The causal
organism of the Armillaria root rot disease in daylily
was identified as Armillaria gallica H. Romagnesi & Marxmüller
based on genetic fingerprinting. This species is most
prevalent on the west coast and in the mid west of
the United States but is also known to be a pathogen
on trees on the east coast. It produces gill-bearing
mushrooms typically in the fall at the base of infected
trees and sometimes on shallow roots. The mushrooms
grow in clusters, are brown, and possess an annulus
(ring) around the stalk. Cultural or chemical control
options have not been established for this new disease
on daylilies but research is in progress.
Armillaria Root Rot on daylily.
Mycelial sheets in nectrotic tissue of a daylily crown.
Rhyzomorphs intermixed with daylily roots.
Images
courtesy of Dr. Guido Schnabel of Clemson University,
used with permission.
|
