Armillaria root rot—Armillaria mellea
Armillaria root rot, also known as oak root fungus disease
or shoestring disease, affects mostly woody plants but also
affects certain herbaceous perennials, such as begonia,
carnation, daffodil, dahlia, geranium, and peony. Armillaria infects
and kills cambial tissue, causing major roots and the trunk
near the ground to die. The first aboveground symptoms
are often undersized, discolored, and prematurely dropping
leaves. Branches die, often beginning near the tops of
plants; on herbaceous hosts, stems become discolored and
cankered. Eventually the entire plant can be killed. Armillaria forms
characteristic white mycelial plaques that have a mushroomlike
odor when fresh. Mycelia grow between the bark and wood
on woody hosts and can grow through soft plant tissue and
appear on the surface, especially with herbaceous hosts.
Clusters of mushrooms may form at the base of infected
woody plants. Black or dark reddish brown rootlike structures
(rhizomorphs) are frequently attached to the surface of
roots or the root crown.
Solutions
Preventing infection of new plants and planting
resistant species are the only effective controls for Armillaria.
Prepare the site well. Remove old roots and debris from
the soil before planting. Use pathogen-free plants and
air-dry soil well before planting. Provide plants
with appropriate cultural care, especially proper irrigation,
and adequate drainage.
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White mycelium underneath bark
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