Cedar Apple Rust by Mark Person

Mark Person has been in the industry for over 40 years. With a degree in Horticulture from University of Nebraska, Mark has been putting his knowledge to use at Helena for 23 years. Currently, he is a branch manager in Kansas.

Cedar Apple Rust is an unsightly fungal pest that can be economically devastating. This disease is commonly found in crabapple trees and other landscape ornamental plants in the Midwest and Northeast regions of the United States.  

Cedar Apple Rust  is unique because it overwinters on Junipers or cedar plants. Brown, brain-like balls form in the fall, while gummy, orange, tentacle-like projections appear in the spring. The tentacle-like projections are caused by overwintering. The spores are released from the pest when the tentacles begin to develop. With wind and other natural causes, the spores land on crabapple trees and other plants. The pest then begins to affect the leaves and the fruit on these targeted plants.

The largest problem that Cedar Apple Rust causes is defoliation. With appearance being at utmost important in landscape ornamentals, the unattractive appearance of this disease devalues the tree. Cedar Apple Rust can also weaken the tree. With less reserves in the tree, the tree will become weaker and of less value.

It is vital that Landscape Architects take into account disease management when facing Cedar Apple Rust. One of the recommended control methods is the placement and location of the trees. Native and planted cedars can spread this disease to nearby susceptible trees. It is advised to place these cedars far enough apart or separate them from plants that are susceptible to Cedar Apple Rust. Another control method is to keep fallen leaf and fruit debris cleaned up in the fall. The infection may blow from nearby cedar, and cleaning the plants can protect it.

Implementing a spray program is another method to protect crabapple trees and others from Cedar Apple Rust. With a spray program beginning in Mid-April to early May or when tentacles begin to appear, two to three applications are suggested. The first and third application should be a prophylactic application using a copper herbicide like Badge®, and the second application should be a contact + systemic application using a fungicide like Chlorothalonil with Thiophanate Methyl, such as Spectro® 90. In addition to herbicide applications, it is also advised to apply Renova® for stress management  or Orbix® for foliar nutrition.

For more solutions to Cedar Apple Rust problems, and to find the right products for you, contact your local Helena representative.

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