Crataegus fruit, better known as hawthorn berry, grows on the hawthorn (Crataegus) shrubs and trees of the rose family. Hawthorns stand between 15 and 30 feet high, with glossy, green summer leaves. Some varieties have orange or purple fall foliage. Their abundant white, pink or rose spring flowers give way to small summer berries that ripen to red. Hawthorns are susceptible to cedar-quince rust, a fruit-affecting fungal disease.
Cedar-quince rust (Gymnosporum clavipes) is a fungus requiring two hosts--one of the juniper and one of the rose family--to survive. The fungus spends part of its life cycle overwintering in a juniper family host before spreading in spring to its rose family--in this case, hawthorn--host. Eastern red cedar is a common juniper host for the fungus. Cedar-quince fungus affects numerous rose family plants in addition to hawthorns, according to the Missouri Botanical Garden Integrated Pest Management website.
The fungus infects hawthorns in spring as wind carries spores from the juniper hosts to the hawthorn plants. The infectious period can continue into June, according to Kansas State University Department of Plant Pathology. The fungus then produces spore tubes on the hawthorn's twigs and fruits. The tubes release the spores in summer for wind transportation to juniper hosts, where the cycle will repeat the following spring.
Crataegus fruit fungus' disfiguring effects on the plants' twigs, fruit and branches have a serious impact on commercial nursery hawthorn production. Damage is most severe at nurseries where local juniper populations serve as alternate hosts for the fungus, according to Kansas State University Department of Plant Pathology.
Cedar-quince rust fungus infests hawthorn's new stems and fruit. Between a week and 10 days after infestation, the stems and fruit swell or develop spots. Tiny black dots appear in the spots a few days later. Pale pink, spore-containing tubes that frequently cover the fruit develop over the course of four to seven weeks, notes the Missouri Botanical Garden. Infected branches develop cankers. The growths encircle the branches after two years, causing dieback.
Controlling the Fungus
Begin control of crataegus fruit fungus by removing the spore-containing tubes that develop on nearby juniper hosts, if the number of affected trees is small and the infestation isn't serious. Replace juniper family plants with evergreens not susceptible to the fungus. No hawthorn is immune to the fungus.
Use a fungicide registered for use against cedar-quince rust to protect your hawthorns' new growth. Apply it when the fungal galls on nearby junipers are releasing the orange gelatinous material that contains their spores. Follow the manufacturer's directions regarding fungicide application.