Agriculture Reference
In-Depth Information
Do not interplant your orchard crops with Verticillium-susceptible crops.
Control weeds, and avoid excessive nitrogen fertilization, irrigation, and
severe pruning. The goal should be moderate vegetative growth and sustain-
able, high yields. Remove and destroy dead and diseased branches, prefer-
ably before the leaves fall and add more inoculum to the soil.
Armillaria Fungus
Armillaria or shoestring fungus is a fungal pathogen (
Armillaria mellea
). Al-
though sometimes called oak root fungus, it attacks the roots of more than
500 species of woody plants, including orchard crops. Armillaria is wide-
spread in North America and most often found where forests or woodlots
have been cleared fairly recently. Honey-colored mushrooms that appear in
fall or winter are the fruiting stage of the pathogen, but their spores seldom
infect host plants directly.
Symptoms.
The fungus grows underground, producing dark, root-like
strands (rhizomorphs) in the soil. Infected plants often show characteristic
white “fans” of fungal mycelium just beneath the bark on the upper roots and
lower trunk, to about 12 inches below the soil surface. Use a knife to scrape
away the outer layers of bark to expose the fan.
Aboveground symptoms can be very hard to detect. Shoots and leaves
are small, but infected trees can appear reasonably healthy until suddenly
dying, usually at the onset of hot weather.
Management.
Simply removing an infected tree or shrub does not eliminate
the disease, which can live for years on dead and decaying roots. Healthy
plants become infected when their roots contact live or dead infected roots
of another plant. Rhizomorphs that grow out into the soil from infected roots
also carry the fungus to new plants. Control involves prevention. Even soil
fumigation has not been very successful.
