Diseases of Goldmound Bushes

Fire Blight

• Fire blight is caused by the bacterium Erwinia amylovora. Spireas and other plants are usually infected through open flowers or succulent tissue, with infected flowers, shoots and leaves wilting and turning black. Cankers develop on infected wood, producing a watery, tan ooze that turns dark upon exposure to air. The ideal conditions for infection are daytime temperatures between 75 and 85 degrees Fahrenheit and high humidity or rainy conditions. Regularly monitoring and promptly pruning out and disposing of infected parts of the spirea and other plants is crucial. Also avoid heavy pruning and excessive nitrogen fertilizer applications, which encourage a flush of succulent new growth vulnerable to fire blight.

Leaf Spots

• Spots on a spirea's foliage are likely the result of a fungal infection, which may slightly impact the spirea's appearance but is likely not serious enough to warrant fungicide treatment and will have little impact on spirea health. Promptly raking up and disposing of fallen leaves, pruning off heavily infected portions of the spirea when conditions are dry and avoiding overhead watering or sprinkler irrigation will generally address leaf spots sufficiently.

Powdery Mildew

• The fungal disease powdery mildew is easy to recognize on a "Goldmound" spirea, causing powdery white fungal growth to develop, primarily on leaves and shoots. New growth may be dwarfed or distorted and covered with white growth. Powdery mildew spores spread via wind and, unlike most fungi, do not require free water on foliage to infect a plant. Shady conditions and temperatures between 60 and 80 degrees F favor powdery mildew development. To avoid problems with powdery mildew on "Goldmound," position the plant in full sunlight or prune off overhanging branches on adjacent vegetation to increase the amount of light reaching the spirea and improve air circulation. Avoid fast-release or excessive nitrogen fertilizer applications, which encourage a flush of new growth particularly susceptible to powdery mildew. If other fungal diseases are not a concern, use overhead irrigation to water the spirea foliage in early morning. This can wash powdery mildew spores off of leaves or kill the spores.

Root Rot

• Spirea is susceptible to Phymatotrichum root rot, also known as cotton root rot or Texas root rot. Infection usually becomes apparent in summer when soil temperatures climb to about 80 degrees F. Leaves on affected plants dry out and turn brown but remain attached to the plant. Roots are severely decayed, and patches of white to tan spores may appear on the soil surface near killed plants. If the root rot damage is not yet extensive, spreading compost or aged manure in a layer two inches thick around the plant, then applying both sulfur and ammonium sulfate over the material, each at a rate of 1 pound per 10 square feet, and watering the material in thoroughly may offer control. If damage is severe, remove the spirea and replace it with a species resistant to this disease.