Orange fungus on apple leaf. Picture provided by Beth Witherup
Hi Ruth,
It looks like we have some sort of orange fungus growing on our apple trees. What is the best way to fight this while keeping our apple trees organic?
Thank you,
Beth
Dear Beth,
Cedar Apple Rust on Foliage, Photo from NC State
The orange spots on your apple trees are a type of rust. Apples are susceptible to three kinds of rust: cedar apple rust, quince rust, and hawthorn rust. All three rusts are caused by spores that overwinter as galls on trees in the juniper family – especially the Eastern red cedar, Juniperus virginiana. Spring rains cause the galls to swell and produce gelatinous “horns” that start producing spores. Only ONE large gall can produce billions of spores. The spores are quickly released during wet periods in spring, and are carried on air currents infecting apples, crabapples, quince, pear, hawthorne, serviceberry, and mountain ash. Cedar apple rust galls resemble something from outer space, and their spores can travel over 2 miles. Hawthorne rust spores have been known to travel almost 14 miles. What? Yes…14 miles. In late summer the apple (or host tree) produces spores that can, in turn, infect the cedar tree. Here is a chart about all three rusts.
Cedar Apple Rust Gall with Telia, Photo from NC State
The primary infection period on apple trees is between the pink stage and three weeks after bloom. Once the spores have been released for that year, there is no secondary infection period. Most of us won’t even notice that our trees have rust initially, but by early summer the orange spots on leaves and fruit are easily visible. Once the trees have been infected, there is not much you can do for that year.
OPTIONS FOR CONTROL OF RUST for Organic Gardeners:
Eastern Red Cedar Tree, Photo from NC State
- Removal of Cedar Trees: Eliminating all red cedar trees within at least a 500’ radius (preferably a 2 mileradius) of apples and other susceptible trees would be the ideal remedy for this problem, but that is impossible in urban settings.
- Planting Resistant Varieties: From an organic maintenance perspective, choosing rust-resistant apple varieties is imperative, and more than one Cooperative Extension site emphasized the importance of selecting resistant cultivars. Farmer Tom Elmore grows only disease-resistant apple varieties and he reports seeing very little rust on his trees. However I have seen a lot of rust showing up on cultivars that are less disease resistant. Choosing resistant cultivars is tricky because a particular cultivar may be very resistant to cedar apple rust, but highly susceptible to quince rust. Cultivars must be cross-referenced for resistance to each one of the rusts. The most important rust to watch out for in WNC would be cedar apple rust. Additionally, I highly recommend cross referencing apple cultivars for susceptibility to the dreaded fire blight (very prevalent in the southern Appalachians). Here is a chart that cross references the main apple diseases. I suggest cross-checking lists on various sites, checking for updated lists, and finally compiling your own list – especially if you are researching fireblight resistant varieties because sometimes the information is conflicting.
Cedar Apple Rust Aeciospores on Leaf, Photo from NC State
Rust Prevention with Fungicides/ Fungicide Possibilities:
If you have a susceptible tree that you want to protect from rust, organic solutions can be tough. The key words here are prevention and timing. Proper timing of the fungicide applications is vital to prevent rust. Fungicides should be applied from the pink stage until about three weeks after bloom. For Certified Organic growers, many of the allowed fungicides were allowable only with restrictions, so growers should check with their certifier before application of fungicides. According to the labels – Seranade, Copper, Oxidate, 70% Neem, and Sulfur will control rust, but it is somewhat mind-bending to navigate the particulars of the next paragraph.
- Bordeaux mixtures are a combination of copper sulfate and lime (calcium hydroxide) and they work to control both fungus and bacteria (like fire blight). Baby leaves are very sensitive to copper, so bordeaux mixes are usually applied when the plant is dormant.
- Copper should not be applied from 1/2” green through 4-5 weeks past bloom as it can cause damage to fruit (russeting) and leaves, and should always be used cautiously once foliage appears. Many coppers are not labeled for use on apples past petal fall.
- Fruit/leaf damage is also a concern when using Lime-Sulfur after tight-cluster (lime-sulfur is really a dormant spray that should not be applied to plant foliage).
- Oxidate can also cause russeting and must be applied at exactly the right time to be effective.
- Sulfur washes off easily, so you may need to re-apply it every 3-5 days and you will need to apply it just BEFORE it rains (do not use sulfur if you have applied an oil spray within the last month or when temperatures are expected to exceed 80°).
- Applications of Neem should begin at the first sign of spring budding. Neem oil should be applied late in the day to prevent leaf burn and to protect bees.
- Unfortunately, Neem and Serenade were not fully discussed on Cooperative Extension sites. In all cases the leaves should be coated with the fungicide to the point of run-off.
Orchardist Michael Phillips mentions using elemental sulfur sprays in an older article and micronized sulfur in a
Cedar Apple Rust Aeciospores on Fruit, Photo from NC State
different article. He says, “I use the minimum amount of sulfur I can get away with during this time – about three applications on average” and warns that “sulfur applied in excess…eliminates the microbial allies that are essential for keeping disease under control in a holistic orchard”. In his most recent book, The Holistic Orchard, he uses four holistic springtime sprays at: (1) week of ¼” green, (2) early pink, (3) petal fall, and (4) first cover (7-10 days following petal fall). His holistic spray is a mix of 100% neem with a little soap, liquid hydrolyzed fish, effective microorganisms (EM’s), blackstrap molasses, and liquid kelp. Remember to always read and follow the safety precautions and instructions on pesticide labels.
Whew! What else can you do?
- Buoy the Trees Immune System: Trees with cedar apple rust may lose some of their leaves and fruit quality can be compromised. Over time, defoliation can weaken the trees; so you will want to prevent further stresses to the tree during the growing season. Make sure you provide adequate water during dry periods. Respond quickly to other potential issues like fire blight. Applications of seaweed and compost tea can have a tonic affect. After leaf fall in autumn, remove infected leaves and fruit from the property.
- Provide Just Enough Nitrogen: New succulent green growth is always more susceptible to diseases and insects. Provide adequate amounts of nitrogen for growth, but not so much that you have an abundance of succulent growth. This is particularly true with fruit trees because your objective is to harvest fruit, not leaves. As an organic gardener, pay attention to the details of nature and use this knowledge to your advantage.
Beth, I hope this answer helps with next year’s apple crop. Bottom line…if you don’t want to spray at all, only buy cultivars that are known to be resistant to the main pest pressures in your locality. And always give your plants what they need to be strong and resilient.
All my best,
Ruth
Want to network with other farmers? Consider joining CRAFT: A farmer-led effort to bring established farmers, farm apprentices, and aspiring farmers together for year-long training in the art and science of sustainable agriculture, straight from the hearts, mouths, and fields of seasoned local farmers in Western North Carolina (WNC).
Ruth Gonzalez is a former market farmer, gardener, local food advocate, and founder of the Tailgate Market Fan Club where she blogs at http://tailgatemarketfanclub.wordpress.com. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.
Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School
Ask Ruth © 2013 Ruth Gonzalez & Organic Growers School
Author: Ruth Gonzalez
Ruth Gonzalez is a former market farmer, gardener, and local food advocate who wants to see organic farms proliferate and organic gardens in every yard. She also served on the Organic Growers School Board of Directors. In her job at Reems Creek Nursery, Ruth offers advice on all sorts of gardening questions, and benefits daily from the wisdom of local gardeners.
Hi Ruth, Thank you for the article. It seems that the treatment needs to be of at an early apple growth stage.
My apple trees have cedar-apple rust on leaves. I did not notice the disease until now (early summer) when the orange spots appear on the older leaves (not seem to be on the new leaves). Is there still treatment at this stage?
For the most part the damage is done. Best to spray copper around early to mid-spring or around blossom stage. Also consider removing any eastern red cedars on your property if you’ve got them. If you don’t want to cut down the eastern red(s) (which are prized by many a bird!), hand pick the fruiting bodies of cedar apple rust in late winter.
I also discovered the rust after spots appeared on leaves. So am I to gather that there is nothing to do at this stage? Also, for next spring, is there a mixing ratio formula for Michael P. formula mentioned above?
Looking back on the articles we have by and about Michael Phillips, no reference is made to mixing ratios for the formula he shares. When creating compound mixes myself, I simply follow the directions for each product. With soap, which serves to hold the mixture to the leaves, an ounce per gallon seems to do it for most sprays — 2 oz won’t kill less hardy plants than apple trees. Note that by 100% Neem, Phillips is referring to the oil imported from India. You may want to contact one of the holistic orchards listed here for more information on your options.
Hey, Ruth! such a great post dear i really liked it. keep sharing. cheers!
Help!
My apple seeding has rust!
What do I do!?
Hi Elaine, I have a few questions which will help me find a solution to your problem: Is your plant a newly grafted tree? Is it in the ground or in a pot? How long has it been planted?
My husband bought a Cortland Apple and a Gala Apple from TSC, both potted. They both have apple rust. Do I just plant the trees and treat them next spring or is there something I should do now?
My tree is infected. Am I correct there is nothing to do now? Just let the tree do its thing this season and at the end of the fall spray it then spray again at the beginning of spring?
Hi Folks,
I would plant the apples that are still in pots right away. Even though the weather is hot, plants in containers are usually more vulnerable to stress because they dry out more easily than plants in the ground. Once they are planted, keep them well watered. Using common sense to moderate this advice if needed, I recommend watering your apples twice a week deeply to the bottom of the root ball until mid-December and then start watering again around mid-February or when you see the buds beginning to swell. It takes 1-2 years for a plant to become established.
There is not a lot you can do at this point for the rust, as it must be prevented early in the year. Preventing further stress to the apple tree is one thing you CAN do now — make sure it is well watered and that the mulch is not touching the trunk of the tree. If trees are infected with rust every year eventually it can begin to compromise the immune system of the tree. If you have an Eastern Red Cedar tree in your yard, then remove the tree (see article for more details), but the spores can travel quite a distance (miles). Choosing apples that are not prone to rust and fire blight is recommended — my two top choices are Liberty and Enterprise.
Next spring use fungicide sprays to prevent rust. The timing is very specific and is detailed in the article, along with fungicide recommendations and deeper information.
All my best,
Ruth
I have a question about the cedar Apple rust…we have a Snowsweet variety apple tree. If I bagged the apples (using plastic sandwich bags, for pest control) in early June, before the rust spots showed up on the leaves, will that help prevent spots on the apples themselves? Thanks.
HI what is best fungicide I can use on my cedar tree to stop apple rust?
Hello my apple tree is new just planted in the garden 3 weeks ago, still with flowers I just noticed the rust spots on a few leafs,last week I spayed neem oil just once but they advised me to use all seasons spray oil.I wish I could include pictures to show you…should I spray the air or is not useful anymore? Thank you.
Hello, I have a ? about rust. I grew a bunch of apple trees from seed. They can be any of these varieties when full grown (Envy, Honeycrisp, Gala or Juici) don’t matter to me what they are lol, but I noticed on the leaves this year – rust. They are 2 – 3 yrs old at this point. I have no juniper or cedar trees on my property of 5 acres in Southwest Pennsylvania (that’s not to say my neighbors don’t). What can I do to keep the rust from continuing year after year? I just now planted peach, cherry, pear, blueberries, elderberries, serviceberries, strawberries and a variety of blackberry and raspberry plants (yes, I’ve been extremely busy 🙂 ). I would also like to know if this will affect any of my other plantings? Thank you so much for your time. Please e-mail a response to me so I know I will see it.
i have a bradford pear tree, and the leaves are falling off and they have colored spots on the leaves, and the trunk and the limbs have like green spots on them, looks like an algae or something, what can i do?? i did spray on a disease control from lowes and sprayed the leaves and sprayed around the trunk also.
Hello Jackie. Thanks for your question. Ruth recommends you take quality pictures (from both close up and far away) and a fresh sample of the leaves to the Cooperative Extension in your county and confirm what the problem actually is. There are many moving factors…has the weather been wet or dry? Is there drought stress? Lots of rain often creates perfect conditions for leaf spot. Has the tree been over-fertilized? Is there air movement around the tree? Is mulch touching the trunk of the tree? What time of year is it? Is it nearing fall and the leaves of some trees are starting to decline or even fall off? Closely observe conditions before going to Extension.
I do not recommend applying chemicals when you don’t know what the problem is. Always try the softest, least toxic remedy first.
P.S. Bradford pears are beautiful spring bloomers. Unfortunately they are an extremely invasive plant.
Hello Karen. Thanks for your question. Ruth suggests taking another close read of this article, as proximity to cedars and spray regimens are discussed in the article. Feel free to write back if you have any further questions!
Hello Federica. Thanks for your question. Ruth suggests taking another close read of this article, as proximity to cedars and spray regimens are discussed in the article. Feel free to write back if you have any further questions!
Hi Harold! We will try to email you a response shortly !
Can cedar mulch used around the base cause this as well?
It is possible the cedar mulch could carry the fungus that causes apple rust, so yes!