Can you tell me how to treat my juniper trees for cedar-apple rust?

I have 3 robust juniper trees that  get the rust disease that is caused by an apple tree on a different property. The junipers are not looking very good but I do not want to remove them.


Answer

Cedar-Apple Rust Disease (Gymnosporangiumjuniper-virginianae),and several closely related rust diseases, require two hosts to complete the life cycle of the disease. For cedar-apple rust, that means that both an apple or crabapple and eastern red cedar (or other juniper) must be present within a distance that allows the spores to travel from one plant to the other. 

The first symptoms noticeable on an apple tree are yellow leaf spots that appear shortly after bloom.  A wet spring, particularly just after leaf buds break, will increase the severity and spread of the infection. Sometimes oozing, orange bumps will form under the leaf spots and then become black.  Later in the season, clusters of thread-like fruiting bodies grow from the underside of the leaf spots, as well as twigs and fruit.  Spores that infect the needles of the alternate(cedar) host are transmitted in warm, damp weather.

While the cedar host may not be present on the same property (spores can travel for up to 5 miles), the infection on that plant can be identified by the emergence of a gall six months after spores reach it.  About 18 months later, brown telial horns emerge from depressions on the gall, elongate and become bright orange and gelatinous in the spring rain.  They dry up after releasing spores.  Leaves may fall from the tree, especially in dry weather.

This disease rarely kills its hosts but it can make them unsightly and gradually weaken them in succeeding years of early leaf fall.  While growing the two plants in close proximity should be avoided, removal of a host may not be an effective solution because the spores can travel well beyond the confines of a single property. An important control measure is the placement of trees in an area where sun and air circulation help control moisture.

This guide from the University of Minnesota offers some starting advice on treatment which is time consuming and tricky to maintain. 

Courtesy of NYBG Plant Information Service

  • Last Updated Mar 23, 2021
  • Views 338
  • Answered By Esther Jackson

FAQ Actions

Was this helpful? 1 0

Ask a plant expert

Send us an email or use the question form below.

Submit a question

Before submitting your question, try searching our Plant and Gardening FAQ page and Help Guides. Still need help? Fill out the form below and a plant expert will answer your individual plant and gardening questions. We will respond to questions in the order we receive them.

Your Question
Your Info
Fields marked with * are required.