Black Fungus on the Bark of a Bottlebrush Tree

Root Rot Symptoms

• Phytophthora root rot is a soil-borne disease resembling a fungus that attacks the roots and crowns of tree and plants, causing a wide variety of symptoms. The upper root area and the bark on the trunk or branches of the tree may darken and ooze a gum or sap. Cutting away this diseased area will sometimes reveal reddish brown streaks on the inner bark and outer wood. Leaves may turn dull green, yellow or even reddish or purple. Young trees are particularly susceptible.

Root Rot Treatment

• Proper water management is key to managing root rot. Never allow the soil to become flooded, as the disease thrives in wet conditions. The University of California Statewide Integrated Pest Management Program recommends cutting infected bark away from the crown of the tree and removing soil from the base of the tree all the way down to the main roots. This will encourage the rotting tissue to dry out. Natives of Australia, bottlebrushes prefer soil conditions on the drier side.

Identifying and Combating Scale

• Bottlebrushes are susceptible to scale insects, immobile insects that form dense colonies that may be mistaken for fungal growth. According to the Agriculture, Forestry & Fisheries of the South Africa Republic, scale insects attack the trunk and branches of bottlebrushes, sometimes causing branch dieback and the death of the whole plant. Prune off heavily infested branches and prune to open up the tree's canopy. Direct sunlight can help combat the pests. Avoid broad-use insecticides in the garden, which kill beneficial predators.

Culture for a Healthy Bottlebrush

• Help prevent both Phytopthora root rot and scale by planting your bottlebrush only in a well-draining soil. If soil drains poorly, mix it with compost to improve drainage. Allow the top layer of soil to dry out in between waterings. Lemon bottlebrush (Callistemon citrinus) is hardy in U.S. Department of Agriculture plant hardiness zones 8B through 10, while stiff bottlebrush is hardy in USDA zones 9 and 10. Weeping bottlebrush (Callistemon viminalis) may grow in USDA zones 9 through 11. All three prefer full sunlight. Fertilize in the spring with a 1/2 to 1 pound of a 10-10-10 or 10-6-4 fertilizer. Where borderline hardy, mulch in autumn to provide winter warmth.