Root Rot in Hydrangeas

Armillaria Root Rot

• Signs of Armillaria root rot include sudden wilting of shoots, formation of white mats of fungi under the bark, threads of black fungi on the roots, and clusters of mushrooms on the roots, according to the Alabama Cooperative Extension System.

Phytophthora Root Rot

• The Alabama Cooperative Extension System notes that phytophthora root rot usually affects hydrangeas grown in containers, but it can occur in landscape shrubs as well. Signs include sudden wilting, brittle and brown roots, and brown discoloration below the bark.

Causes

• Armillaria fungi are often present in the soil without causing any damage. However, when the shrubs are in a weakened state from drought, wounds or stress, the fungi can infect the plant. Phytophthora root rot is frequently caused by poor drainage and overwatering.

Treatment

• Fungicides are used to treat phytophthora root rot but are not effective in controlling Armillaria root rot, according to the Alabama Cooperative Extension System.

Prevention

• Prevention of Armillaria root rot includes planting in appropriate growing conditions, fertilizing, watering during periods of drought and removing diseased plants. To prevent phytophthora root rot, do not allow water to collect, and mix fungicide into the soil.