Root rot in trees and shrubs is treated by exposing the root crown to air and removing already-dead roots to stop the infection from spreading, then applying a systemic phosphite fungicide labeled for the fungal pathogens that cause it. How early treatment starts matters more than which product is used, since root rot that has already caused extensive root loss is far less likely to respond to any treatment.

What causes root rot in trees and shrubs?

Root rot is caused by soil-borne fungi, most often Armillaria, Phytophthora, or Phymatotrichum (also called cotton root rot or Texas root rot), that attack and decay a plant's root system. These pathogens are most active in poorly drained or heavy soil, since wet, oxygen-poor conditions around the roots are exactly what let them take hold.

What are the early symptoms of root rot?

Dulling leaf color and a general loss of vigor are usually the first signs, followed by wilting, yellowing, or browning foliage and dieback in major branches. A fruiting plant may bear fruit only on its upper branches while the lower branches stop producing, and digging near the base often reveals decaying roots with brown discoloration under the bark. Small white mushrooms or fan-shaped fungal growths at the base of the trunk are a later, more visible sign, and left untreated, root rot leads to rapid decline and death.

Does root rot affect shrubs the same way it affects trees?

Yes. Root rot's fungal causes, Phytophthora, Pythium, and Armillaria, affect shrubs and other woody ornamentals as well as trees, so a shrub showing dulling leaves, wilting, or fungal growth at its base responds to the same treatment as a tree: exposing the root crown and applying a systemic phosphite fungicide.

What is the first physical step in treating root rot?

Exposing the root crown to air by removing 3 to 4 inches of soil around the base of a newly infected plant reduces the wet, low-oxygen conditions the fungus needs, and digging out and removing already-dead roots keeps the infection from spreading further into healthy root tissue. This physical step matters alongside fungicide treatment rather than instead of it, since neither step addresses what the other one does.

What is the best fungicide treatment for root rot?

Garden Phos Systemic Fungicide is absorbed by the plant and moves through its vascular system, and its own label lists root rot, collar rot, crown rot, and phytophthora- and pythium-related root disease among what it controls. Applied as a foliar spray, it is reapplied every 14 to 21 days, or it can be used as a soil drench applied about once a month; one pint of concentrate makes roughly 24 to 48 gallons of foliar spray or about 768 gallons of soil drench solution.

Is there a trunk-application option instead of spraying the whole plant?

Garden Phos with Pentra Bark delivers the same active ingredient through a concentrated spray applied to the lower 8 feet of the trunk rather than the full canopy, and its own label lists root and collar rot alongside phytophthora- and pythium-related diseases for that application method. This trunk-spray option is useful on a large tree where covering the whole canopy with foliar spray is impractical.

Can a plant already showing severe dieback or fungal growth at the base still be saved?

Sometimes, but the odds drop the further the infection has progressed. A plant caught at the dulling-leaf-color stage responds far better to the combination of exposed roots and systemic fungicide than one that already has extensive root decay or large fungal growths at the base, where enough of the root system may already be gone that treatment can only slow further decline rather than reverse it.

Frequently Asked Questions

Can improving soil drainage alone prevent root rot without fungicide?

Not once an infection is already active. Better drainage reduces the wet conditions the fungus needs and helps prevent a reinfection later, but an established infection still needs direct fungicide treatment rather than a drainage fix on its own.

Is Armillaria root rot as treatable with fungicide as Phytophthora root rot?

Both are covered by the same systemic phosphite fungicide, but Armillaria tends to persist in soil and old root and stump material longer than Phytophthora, so removing dead root material thoroughly matters even more when Armillaria is the cause.

Should mulch be kept away from the base of a plant recovering from root rot?

Yes. Mulch piled against the trunk traps moisture right where the treatment is trying to keep the root crown dry and exposed to air, working against the recovery rather than supporting it.

Can a plant with mushrooms growing at its base still be saved?

It depends on how much of the root system is still healthy. A few small mushrooms on an otherwise vigorous plant is a different situation than mushrooms appearing alongside significant dieback, where the root damage is likely much further along.

How long does root rot treatment take to show results?

Improvement is gradual rather than immediate, and how much root system was already lost before treatment started has more influence on the timeline than the fungicide itself. A plant treated early, before significant root loss, typically shows steadier recovery than one treated after extensive symptoms were already visible.