Serviceberry Diseases

Rusts

• During warm, rainy springs in their growing range across U.S. Department of Agriculture plant hardiness zones 2 through 9, serviceberries may serve as alternate hosts for cedar-hawthorn and cedar-quince rusts (Gymnosporangium spp.). They frequently contract the diseases from wind-carried spores released from cankers on Eastern red cedars (Juniperus virginiana), also hardy in USDA zones 2 through 9. Infected twigs develop cankers packed with fungal strands that spread into leaf buds and stems. Cedar-quince rust causes leaf buds to open prematurely, producing stunted, misshapen foliage. Berries shrivel and die. Plants infected with cedar-hawthorn rust develop orange-red leaf spots covered in spore-filled tubules, which also appear on the fruit. To protect your serviceberries, remove nearby rust-hosting Cypress (Cupressaceae) family plants. If that's not practical, spray your serviceberries with ready-to-use chlorothanolil fungicide or another fungicide registered to treat rust on serviceberries in your area. Treat them according to the label’s specifications when their new growth appears in spring.

Entomosporium Leaf Spot

• Small, round red spots expanding into large dead patches on your serviceberries' leaves result from Entomosporium leaf spot fungus. The disease spreads when spring or fall rains, wind or overhead watering splash spores onto your plants from previously infected plant debris. Prevention begins at planting. Give your serviceberries full sun, with plenty of space between plants to limit the infection-encouraging moisture buildup. If Entospomorium leaf spot strikes, prune the infected leaves and dispose of them, along with fallen ones. Always water from beneath to avoid splashing spores from the soil onto the plants.

Fire Blight

• Potentially fatal fire blight results from Erwinia amylovora bacterial infection. Splashing rain, honeybees and other insects carry the bacteria from cankers on contaminated trees to healthy ones in spring. Symptoms include oozing twigs, trunk and branch cankers, wilted flowers and -- as the infection worsens -- blackened leaves, flowers and fruit. Fire blight may kill young serviceberries. To limit the damage, prune the infected parts when symptoms surface, cutting back to 10 inches below visibly diseased areas. Between cuts, rinse your tools in a solution of 1 part household bleach to 9 parts water, so you won't accidentally spread the germs to healthy tissue.

Powdery Mildew

• Watch for powdery mildew fungus on your serviceberries in mid to late summer, especially if the weather is dry and your plants get significant shade. This occasional and seldom-serious disease causes floury, white leaf blotches. Wind transports its spores from infected to healthy plants, where it may stunt or distort new growth and cause premature leaf drop. Symptoms seldom warrant chemical control. To manage the infection, prune the blemished foliage. Unlike many fungi, powdery mildew germinates on dry surfaces. Overhead watering dislodges spores already on the leaves and keeps the ones that land later from germinating.