Root Rot (Phytophthora, Phythium, Armillaria)

Occurrence: Develops gradually over a period of month or years.

Root rot results from infection by any of three soil-borne fungi. Phytophthora, Phythium , and Armillaria root rots spread most quickly in warm, moist conditions.

Phytophthora limits the amount of moisture and nutrients the plant can absorb. Affected plants become weak with wilting, yellowing, or bronzing foliage and dying branches. Lifting infected plants’ bark at the soil line frequently reveals wet, oozing cankers or amber staining on the underlying wood. Phytophthora destroys new, white roots and leaves root balls black or cinnamon-brown. Pythium affects new seedlings and causes similar symptoms as Phytophthora.

Armillaria fungus survives in the stumps or root fragments of previously infected trees and attacks stressed plants. Armillaria attacks roots and decays the wood. Affected plants may exhibit prolonged, generalized weakening or remain symptom-free until they topple in heavy wind because of root damage. Honey-colored mushrooms sprouting at the plant’s feet in autumn are symptoms of Armillaria.

Root rot symptoms are general discoloration of foliage and eventual death. Roots are discolored below the bark in the region of the cambium. Roots in advanced stages are highly decomposed and break off easily.

Conditions Favoring Disease Development: Poorly drained and wet sites where oxygen depletion to the root is likely. Planting root balls too deep, overwatering it or mulching it too heavily raises its risk of root rot.

Control: Plant resistant species in deep, well-drained soil and after plant is established use proper watering practices to maintain moisture in soil, but avoid keeping the soil wet. Deep watering is ideal. Soil should dry out between watering cycles. Chemical control is not recommended because most likely the plant is too far gone by the time root rot is identified to have success.