Is Cedar Apple Rust Harmful to Humans? Find Out the Truth

Cedar apple rust is a fungal disease caused by Gymnosporangium juniperi-virginianae, which affects apple and red cedar trees, as well as ornamental junipers. This disease may result in premature defoliation and reduced fruit quality in apple trees, while it can be disfiguring for cedar trees [1]. Although cedar apple rust can weaken trees and lower their resistance to other diseases and pests, it doesn’t directly pose a threat to humans.

However, it’s worth mentioning that individuals who have allergies or sensitivities to mold and fungi might experience allergic reactions when exposed to cedar apple rust spores [2]. It’s important for those individuals to exercise caution and limit their contact with affected trees during the fungal life cycle. In general, cedar apple rust is more of a concern for horticulturists and apple growers; proper management practices can help reduce the spread of the disease and minimize the damage to affected plants [3].

Cedar Apple Rust Overview

Gymnosporangium Juniperi-Virginianae

Cedar-apple rust is caused by the fungus Gymnosporangium juniperi-virginianae. This fungus affects plants from two families: Cupressaceae (eastern red cedar and other junipers) and Rosaceae (apple, hawthorn, serviceberry) 1. The disease may cause damage to the health and vigor of apple trees, and although it is not highly harmful to cedar trees, it can cause cosmetic disfiguration 2.

Life Cycle

The life cycle of cedar-apple rust involves two hosts: apple and red cedars / ornamental junipers 3. The fungus forms galls on juniper trees, which release spores into the wind during wet weather. These spores then infect apple trees, causing leaf spot symptoms and premature leaf defoliation 4. In later stages, the fungus produces spores on the apple tree that can infect junipers, completing its life cycle.

Comparison Table

Feature Gymnosporangium Juniperi-Virginianae Cedar Apple Rust
Fungal Pathogen Yes Yes
Host Plants Junipers and Apples Junipers and Apples
Life Cycle Stages Two Stages (Juniper and Apple hosts) Two Stages (Juniper and Apple hosts)
Damage on Apple Trees Leaf spots, premature defoliation Leaf spots, premature defoliation
Damage on Cedar Trees Cosmetic disfiguration Cosmetic disfiguration
  • Characteristics of Cedar-apple Rust:
    • Caused by a fungus (Gymnosporangium juniperi-virginianae)
    • Infects plants from two families (Cupressaceae and Rosaceae)
    • Requires two hosts (apples and junipers) to complete its life cycle
    • Can cause damage to apple trees and disfiguration on cedar trees

Susceptible Hosts

Apple Trees

Cedar apple rust, caused by the fungal pathogen Gymnosporangium juniperi-virginianae, affects apple trees. The disease infects the leaves and fruit of susceptible cultivars.

  • Symptoms: Bright orange to red leaf spots; possible premature defoliation if infection is severe
  • Examples of hosts: Apple trees, crabapple trees

Juniper Trees

Juniper plants, such as eastern red cedar, serve as an alternate host for cedar apple rust; the disease requires both apple and juniper hosts to complete its life cycle.

  • Symptoms: Galls on branches and treetops; potential disfigurement
  • Examples of hosts: Eastern red cedar, other juniper species
Characteristic Apple Trees Juniper Trees
Host Species Apple, Crabapple Eastern Red Cedar, Juniper
Infected Parts Leaves, Fruits Branches, Treetops
Symptoms Orange-red leaf spots, premature defoliation Galls, disfigurement
Impact Reduced fruit quality, tree vigor Generally not harmful, cosmetic damage

Symptoms and Damage

Effects on Apple Trees

Cedar Apple Rust is caused by the fungal pathogen Gymnosporangium juniperi-virginianae. On apple trees, it can:

  • Infect leaves and fruit
  • Cause premature defoliation if infection is severe1

Some symptoms include:

  • Yellow spots on upper leaf surfaces
  • Rust-colored spots on lower leaf surfaces

For example, in comparison to a healthy apple tree, an infected one may have:

Healthy Apple Tree Infected Apple Tree
Green, vibrant leaves Yellow, rust-colored spots on leaves
No twig dieback Twig dieback

Effects on Juniper Trees

On junipers, mainly Eastern red cedar and ornamental cedar (Juniperus spp.):

  • Cedar Apple Rust is not known to be extremely harmful2
  • Galls may form on branches1

Galls caused by G. clavipes and G. globosum are smaller than those caused by Gymnosporangium juniperi-virginianae.

In bullet points, the main characteristics of Cedar Apple Rust on Juniper trees are:

  • Formation of galls
  • Less harmful compared to apple trees.

Management and Control Methods

Cultural Practices

  • Plant resistant apple cultivars to reduce the risk of cedar apple rust infection
  • Remove nearby eastern red cedar and juniper trees as they are hosts for the disease
  • Rake and dispose of fallen apple leaves to minimize overwintering fungi

For example, planting disease-resistant cultivars such as ‘Liberty’ and ‘Freedom’ apples can help reduce the risk of cedar apple rust infection in your orchard.

Chemical Control

  • Apply fungicides during apple tree bud break and early fruit development stage to protect against infection
  • Use products containing active ingredients like myclobutanil or propiconazole
Fungicide Pros Cons
Myclobutanil Effective against cedar apple rust May require multiple applications
Propiconazole Provides broad-spectrum protection Can reduce fruit quality if overused

Remember that cedar apple rust is not harmful to humans, and these control methods aim to protect apple trees and fruit quality.

Impact on Human Health

Cedar apple rust is a disease caused by the fungal pathogen Gymnosporangium juniperi-virginianae, which primarily infects apple, crabapple, eastern red cedar, and other juniper species source. It poses significant risks to the plants it affects, but its impact on human health is minimal.

There are no direct health effects caused by cedar apple rust on humans. The primary concern is its impact on the apple industry, as infected apple trees can suffer defoliation, reduced fruit quality, and tree death in severe cases source.

In conclusion, cedar apple rust is not harmful to human health, but it poses significant threats to the health and vigor of apple trees and related plant species.

Footnotes

  1. https://extension.umn.edu/plant-diseases/cedar-apple-rust 2 3

  2. https://hgic.clemson.edu/factsheet/cedar-apple-rust/ 2

  3. https://content.ces.ncsu.edu/cedar-apple-rusts

  4. https://ohioline.osu.edu/factsheet/plpath-tree-10

Reader Emails

Over the years, our website, whatsthatbug.com has received hundreds of letters and some interesting images asking us about these insects. Scroll down to have a look at some of them.

Letter 1 – Cedar Apple Rust Gall on Juniper

 

What is this?
Location: Gwynn Oak, MD
March 17, 2011 9:01 am
HI,
I have 3 or 4 of these things in my juniper bush. I am not sure what it is and want to know if they are safe to have on the bush and at my front door.
thanks,
Signature: M. Kelly

Cedar Apple Rust Gall on Juniper

Dear M. Kelly,
Abnormal Growths on plants are known as galls, and many are caused by insects and mites, though there are other additional causes for plants to produce galls.  We did a search for Galls on Juniper and we immediately discovered the Cedar Cedar Rust Gall on the University of Michigan Integrated Pest Management for Home Apple Growers web page.  You need to scroll down the page to get the information, which includes:  “Gymnosporangium juniperi-virginianae  Cedar-apple rust is a fungal disease that spends half of its life cycle infecting apple or crab apple trees, and the other half infecting Eastern Red Cedar (Juniperus virginiana) or other species of juniper (Juniperus sp.). This disease can cause damage to leaves and fruit of very susceptible apple varieties, but is only a minor problem on resistant or partially resistant trees.”  There is also a nice photo of the gall on FlickR.

Thank you very much for the information!!!!
I will cut them off and dispose of them and follow up and read the web pages you included in your response. Not that I like it, I can deal with a fungus better than bag worms or other insects.
I appreciate your quick response. 🙂
M Kelly

Letter 2 – Creosote Gall

 

Gall or nest?
August 3, 2009
Hi guys!
I absolutely love your site, and tell all my friends about it! I found a very alien object clinging to a creosote bush behind my house, in Tucson AZ. It is a leafy sphere, about the size of a quarter. The leaves (which don’t look anything like those the creosote leaves) are arranged in whirls, like a grassy daisy, and there is a tiny hole in the center of each. Coming out of each hole are discarded exoskeletons, like those of the grain moth larvae you find in boxes of rice and pancake mix. They are probably only 4 or 5mm long. There is also a bit of silk strewn around the whole thing, which gives it a dewy, sticky look, but I haven’t touched it because I don’t want to be impregnated by some alien insectoid race. What kind of bug could construct such a crazy looking (and beautiful) nest? Or is it a gall of some sort? I am so very curious…
Thanks for your help!
Emily Rush
Tucson, Arizona, USA

Creosote Gall
Creosote Gall

Creosote gall
August 3, 2009
Hi!
Me again. After writing to you, I decided to google “creosote gall”. Don’t know why I didn’t do that first, I guess I was just excited to send you a pic of something you might not have seen before. Apparently my mystery alien sphere IS a gall, caused by, wonder of wonders, a creosote gall midge! I couldn’t find a picture of one though. Any help in this area?
Thanks again!
Emily Rush
Tucson, Arizona, USA

Hi Emily,
Thanks for sending us your photo of a Creosote Gall and doing the subsequent research.  BugGuide has images of the Creosote Gall filed under the species Asphondylia auripila with the information:  “Larvae form galls in creosote bush (Larrea tridentata),”
but if you go to the genus Asphondylia and browse, you will see some images of related Midges that probably look very similar to the Creosote Gall Midge. The only species on BugGuide with images of adults is Asphondylia solidanginis. Species in the same genus often have visual similarities and an expert is required to differentiate one from another.  Unlike the Oak Gall we just posted which was formed by a small wasp, the Creosote Gall is formed by a Midge that is in the order Diptera and is classified with the flies.  The Creosote Gall is a deformation of the plant with the leaves and stems stunted to form the Gall.  If you follow the taxonomy on BugGuide back to the Family Cecidomyiidae, you start to get a bit more information, including:  “Minute, delicate flies with long legs and usually relatively long antennae, and with reduced wing venation” and “more than 1,200 species in 170 genera in North America.” There are images of many different species on the Cicidomyiidae page of the Forestry Images website.  Some of the members of the family include the Skeletonweed Gall Midge and the St. John’s Wart Midge.  Those should give you some idea of what the Creosote Gall Midge looks like.  Again, thanks for sending us your photo.

Thanks Daniel!
I hope I can catch a midge in action. By the way, the root borer you posted is a Palo Verde beetle (Derobrachus geminatus). We have lot’s of them in Tucson- they’re HUGE, and they’re really active right now, during the monsoon. I like their fancy spiked collars! Here’s another!
Emily

Letter 3 – Gall or Seed Pod??? Deformed Magnolia Seed Pod

 

Subject: Iowa Gall found under Honey Locust
Location: Des Moines IA
July 31, 2014 5:10 pm
This morning I found this growth on the ground below a honey locust tree. It was under a suburban tree in the Grandview park area of Des Moines with no other trees very close.
I don’t take very good pictures, but the growths appear to underlie some sort of scaled leaves, as each is covered by a tissue with a midline, and there are scale-type structures further down the stem. The stem is woody and it appears some rodent has been gnawing at the base.
It weighs about an ounce and is roughly 6″ long, with 6-10 nodules the size of marbles.
Beyond my curiosity, I’d like to know if this is something we should be concerned about controlling in the trees around where I found it.
Thank you for your time. I can try for better pictures if you need or want them.
Signature: Ash

Seed Pod, we believe
Deformed Magnolia Seed Pod

Dear Ash,
We do not believe this is a Gall.  In our opinion, it is a Seed Pod.  You observation that it was gnawed by a rodent is further evidence that perhaps a squirrel transported it from another tree.  If you open it, we believe you will find seeds beneath what you have called the “nodules the size of marbles.”

I don’t want to disagree, but it is not at all symmetrical, and I’ve been familiar with the native brush and weeds for 50+ years. It might be viral. I’ve been an outdoors-woman and hunter all my life. I’m not saying I’ve seen everything, and I am still surprised but mostly it’s been insects I overlooked or invasive species.
I have asked the state entomologist and agronomist and will let you know what they say. If it were a normal plant structure, I would anticipate more symmetry. Also squirrels are almost as opportunistic as rats.
I’ll pass on their feedback.
Thanks for your time!

Please let us know what you learn.

Update:  Deformed Magnolia Seed Pod
Please see this deformed Magnolia Seed Pod on the Missouri Botanical Garden website where it states:  “This magnolia seed pod is deformed due to poor pollination
.”

Very cool! We do have several magnolia species in the area. The scaled structure is very close. I’ll read more, but that looks like a win.

Authors

    by
  • Bugman

    Bugman aka Daniel Marlos has been identifying bugs since 1999. whatsthatbug.com is his passion project and it has helped millions of readers identify the bug that has been bugging them for over two decades. You can reach out to him through our Contact Page.

  • Piyushi Dhir

    Piyushi is a nature lover, blogger and traveler at heart. She lives in beautiful Canada with her family. Piyushi is an animal lover and loves to write about all creatures.

6 thoughts on “Is Cedar Apple Rust Harmful to Humans? Find Out the Truth”

  1. I’m loving the recent gall posts. To me, galls are one of the most beautiful things in the natural world. They are often outwardly beautiful, but even when they are not, the interaction between an insect and a plant that goes on to bulid such a structure is surely one of the most intimate and beautiful interactions in the world. So thanks from a huge gall fan.

    Reply
    • We wish we had time to post more about the relationship between insects and the plants that they form Galls upon, but much of that is already posted in our archives.

      Reply
  2. I just found pods very similar on my Magnolia tree that I planted 10 years ago. I had never seen anything like it until just this spring. Actually it is on 4 of my magnolias and appears to be killing them! Any idea what I can do to stop it? I have taken pictures of the pods but not sure how to add them to this post.

    Reply
  3. I am from NJ and it’s July 29th 2015. I just pulled a handful of deformed pos off my 6′ Magnolia just like the one in the photos above. Should I be concerned, the plant looks healthy enough.

    R. Pichette

    Reply
  4. I have the same issue on my magnolia. Despite the fact it might be an insect the only way to know is to open it. Having opened it you would have found red, round seeds of the magnolia tree that it belongs to. Squirrels often take them and open them up in my blue tip spruce so I find the same red seeds relocated in a different area.

    If you seriously have spent 50+ years exploring outdoors you would have found that discovery is second to curiosity and the best way to answer your own question would be to dissect what you have found and attempt to give more information.

    Reply
  5. How do I treat for Creosole Gall. I have several Croesole bushes dying. What can I use to treat the bushes. Please help me. Thanks

    Reply

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