Tree-Damaging Fungi in Iran: From Armillaria to Collar Gummosis

Much of the sudden dieback of trees in orchards and streets is not a leaf pest; it is fungal rot of the roots, the collar or the butt that has been advancing under the soil for months. In Iran, four groups do serious damage more often than any others: Armillaria, or honey fungus root rot; Ganoderma and butt rot; charcoal rot caused by Macrophomina on pistachio and some fruit trees; and Phytophthora collar rot, which growers know as gummosis. Seeing a fungal fruiting body at the foot of a tree is not always a firm identification of the species, but it almost always means the wood tissue is being lost from the inside, and it has to be taken seriously.

Armillaria: honey fungus root rot

Armillaria appears on plane, fruit trees, conifers and even shrubs in moist soils and old orchards. The classic sign is dark rhizomorph strands under the collar bark and a mushroom smell in the root wood. Honey-coloured caps usually appear at the foot of the trunk in autumn after rain. A tree may carry a thin crown for several years and then die back on one side in a single hot summer. The fungus travels root to root and through stumps left in the soil. Removing a diseased tree without taking out the stump and the thick roots leaves the source of infection right there for the next sapling. No canopy spray cuts any of these routes.

Ganoderma and butt rot

Ganoderma is seen mostly on old urban trees, the street plane trees of Isfahan and Tehran, and sometimes on pine and black locust. Leathery, brown or varnished brackets appear at the foot of the trunk or on surface roots. Inside the trunk a white or spongy rot advances until the load-bearing wall is thin. From the outside the tree has leaves and looks alive, but in a gale, or even under the weight of light snow, it can break off at the base. This is where the owner asks whether it cannot be injected. The honest answer is that lost wood does not come back. Management means assessing the risk, reducing the sail area of the crown, and in advanced cases controlled removal before an accident.

Charcoal rot on pistachio and fruit trees

Charcoal rot, caused by Macrophomina, is well known in the pistachio orchards of Kerman, Rafsanjan and other hot, dry regions of Iran, and it also appears on some fruit trees under heat and water stress. Root and collar tissue turns charcoal-coloured, and the tree may die on one side or entirely at the height of summer. This fungal disease must not be conflated with Sharka in stone fruit; Sharka is a viral disease of the fruit and is not the cause of charcoal rot. Macrophomina comes from the soil and from residues, and takes its chance when the tree is under drought stress, salinity or sun scald at the collar. Regular deep irrigation, avoiding collar wounds from a rotavator, and removing severely infected trees along with their roots matter more than calendar spraying.

Phytophthora and collar gummosis

Gummosis is a familiar name in the citrus orchards of the north and south and in stone-fruit orchards, but the same Phytophthora group rots the collar of plane, apple and even freshly planted saplings in heavy soil. The common signs are gum or wet brown tissue under the collar bark, a yellowing crown, and death of the tree after flood irrigation at the foot of the trunk. In urban landscaping, a lawn sprinkler that wets the collar every day does exactly what a flooded basin does. Prevention means keeping the collar above soil level, keeping mulch off the trunk, and not letting water gather at the base. A soil fungicide, applied early and together with corrected irrigation, sometimes slows the advance; once the cambium is dead all the way round the collar, no bottle of chemical brings the tree back.

A fungus at the foot of a tree is a warning, not decoration

An autumn bracket at the foot of a street plane or a park locust is not a decorative mushroom. The appearance of a fruiting body means the fungal network has been active inside the wood or roots for a long time. The first step is not to pull the cap off and put it in the bin; the first step is to assess the stability of the trunk and collar. A hollow sound when tapped, flaking bark at the base, ants or termites in the rot, and a vertical split all raise the risk of failure. For a tree beside a building, a school or a pavement, a stability specialist should give an opinion. In such cases Farkesht assesses safety first, and only then discusses feeding or pruning.

Prevention starts with wounds, irrigation and soil

• Keep pruning wounds small and cut correctly at the branch collar; a stub or torn bark is a doorway for wood-decay fungi.
• Stop the mower and the rotavator from striking the collar; that small wound is all Phytophthora and Armillaria need.
• Keep irrigation away from the trunk and eliminate flooding at the collar; the lawn should not run right up to the stem.
• Take out the stump and roots of a diseased tree as far as possible before planting a replacement.
• In pistachio and fruit orchards, manage prolonged drought stress and salinity so Macrophomina has less opportunity.
• Correct compacted, undrained soil; root fungi love low oxygen and persistent moisture.

The practical summary is this: identifying the fungal species precisely takes a laboratory and a look under the collar bark, but the management decision is often simpler than the Latin name. If the crown is still full and the rot is localised, correcting irrigation, removing dead surface tissue, strengthening nutrition and monitoring periodically all make sense. If the butt is hollow, the Ganoderma bracket keeps returning and the tree leans towards a building, do not throw money at pesticide and fertiliser. At that point responsibility means planning a safe removal and a replacement of a suitable species, not hoping for a chemical miracle. A grower who buys pesticide every spring without ever looking at the collar usually replaces that same tree two years later at several times the cost. One autumn visit after rain is the cheapest insurance for a street plane and an orchard pistachio. If the laboratory writes down the fungus's name, apply that name to the irrigation plan and to the wounds, not to the pesticide shelf. A bracket returning in two consecutive autumns means the rot is active and the stability has to be assessed again.