We have all gone through it before: the beautiful apple tree in the backyard was looking healthy last year, but this season the leaves are spotty and the fruit is coming in looking deformed and less than appetizing. If this sounds like your apple tree, there is a good chance that it has Cedar-Apple Rust. But, don’t worry, your tree won’t necessarily die as a result of this fungus. In this article we will discuss what Cedar-Apple Rust is, how to detect it, how to treat it, and finally, how to prevent it.
What is Cedar-Apple Rust?
Simply put, Cedar-Apple Rust is a fungal disease. Fungal diseases can be classified into two types: Saprotrophic fungi and Obligate fungi. Saprotrophic fungi receive their nutrition from nonliving organic materials through an act of digestion, or more commonly understood, decay. It is difficult to overstate the importance of fungal saprotrophs in most environments but this can be a topic for another time. Cedar-Apple Rust is a parasite or Obligate fungi that in contrast to Saprotrophic fungi are designed to attack and feed off of living organisms. Cedar-Apple Rust is a fairly complicated fungus in that it requires plant species from two different (unrelated) families in order to complete their life cycle; specifically a plant from the Cupressaceae family (Eastern red cedar, juniper species) and the other from the Rosaceae family (crabapple, hawthorn, and serviceberry species)
What does Cedar-Apple Rust look like?
The life-cycle of Cedar-apple rust begins in late fall and into the winter when woody galls can be found growing on the branches and twigs of juniper and red cedar trees. Come spring time, after a minimum of four hours of rain and temperatures between 50 and 75 degrees, these galls produce spores that look like reddish, brownish, orange gummy tentacles. These thrive in cool, wet environments, but also have the ability to dry and rehydrate several times in one spring. Once dried, the spores travel with the wind for up to two miles until they land on susceptible apple or crabapple species, which makes this disease a devastating threat to agricultural crops. Transmission of the spores can be juniper to juniper, cedar to cedar, and even apple to apple, but it begins at the juniper/cedar host and spreads from there. If your apple tree shows leaf spotting and spotting and deformity of the fruit, you know that it has been infected. There is no concern for death when it comes to the juniper of cedar species, however, there can be some concern for death in the apple and crabapple species. In cases of serious infection where the severity of the leaf spots result in the disruption of the photosynthesis process and subsequently premature defoliation, death then is the result of the tree’s inability to produce food, not technically the rust.
How to treat Cedar-Apple Rust.
A good practice when treating Cedar-Apple Rust is to inspect your juniper and cedar trees in late winter and early spring. If you notice woody galls beginning to form on the twigs or branches, cut them out of the tree, burn them, dispose of them, in short, get rid of them. Old needles and tree debris parts that fall to the ground at the end of the season should be cleaned up as well since these might have infected tissue that could eventually cause the formation of more galls. This cultural practice will greatly reduce the level of infection on nearby apple species, and do so without introducing chemical agents to the landscape. While chemical controls of the fungus are effective when performed properly, they are not always the best solution. Chemical agents should never be used as treatment on fruit meant to be consumed, and if they can be, there is a very strict protocol for application and timing of application. Furthermore, it is not always the best practice to spray even ornamental trees and shrubs with fungicides as this will undoubtedly kill the bad AND good fungi which is beneficial to the overall health of the plant and the surrounding environment. That being said, fungicides that contain the active ingredient Myclobutanil are most effective in preventing Cedar-Apple Rust, but they are only effective if sprayed before symptoms occur in the spring during new leaf development as buds break and begin to blossom. You will need to spray weekly until the dryer warmer months of the summer arrive, at which point treatment is complete for the year. While fungicides will treat the rust, they will not necessarily stop it.This is why preventative measures are most effective to ensure safe and healthy trees.
How to prevent Cedar-Apple Rust.
Because Cedar-Apple Rust can travel up to two miles from the host to susceptible trees, it is difficult to prevent, especially in areas heavily populated in one or both host families. While infection is not a guarantee, if there is any kind of cedar or juniper within a couple miles of an apple species, there is potential for infection. Most infections occur within a hundred feet of the host plant but the rust can travel further distances in the right conditions. The best way to prevent rust from occurring is by enacting two cultural practices. First, don’t plant affected species in range with each other (this practice is not always practical especially in most rural, farm-like areas that are riddled with multiple species of host trees). The second cultural practice is to plant apple tree species that are more tolerant or resistant to Cedar-Apple Rust. Delicious, Enterprise, Golden Supreme, Liberty, McIntosh, and Priscilla are generally very resistant to the fungus.
In conclusion, Cedar-Apple Rust most likely will not kill your apple tree, but it will diminish the aesthetic and the quality of the fruit production. When dealing with this annoying fungus, remember that the most important thing to do is take preventative measures when planting. If your tree is already infected, use caution if using fungicides and be resilient in removing any galls or fallen needles and branches throughout the season.