After learning about some conditions that apple trees can contract, I was surprised to see that there wasn’t a lot of information on how to treat fire blight organically. So, I did some research to find out more. Here’s what I found.
Research from Washington State University has shown that oregano, thyme, and cinnamon essential oils are a viable treatment for fire blight. Use a spray of 23% thyme oil or 60% cinnamon oil on the tree a few times per year. Vinegar sprays have also been found to work.
So, while there are solutions to treat fire blight, how can you identify fire blight, and do these solutions actually work against it?
What is Fire Blight?
Fire blight (erwinia amylovora) is a highly infectious bacterial disease that affects members of the rose family—including apple, pear, crabapple, rose, cotoneaster, mountain ash, hawthorn, quince, spirea, and pyracantha. Fire blight causes browning, blackening, and disfiguring of the leaves and fruit, sometimes killing the tree.
Fire blight spreads most often in the springtime when it’s warm and wet (spreading the fastest when the temperature is above 70ºF). During the winter, fire blight is dormant. This is why providing preventative treatment to the trees is important in handling this disease.
The bad news is that there is no cure for fire blight.
The good news is some treatments prevent the spread of fire blight. With these treatments (and pruning), fire blight will become manageable and have little to no further impact on your trees.
How to Identify Fire Blight
Fire blight can be primarily be identified from branches, flowers, and leaves turning brown or black. This disease resembles the tree being scorched in a fire, hence the name. Unlike other diseases, plants affected with fire blight often retain their brown leaves and flowers. New branches will also bend 180º.
The most common ways to identify fire blight are from the following symptoms:
- Brown branches, flowers, and leaves
- Brown leaves and flowers not shedding
- A scorched appearance
- A 180º bend in branches (“shepherd’s crook”)
- Cankers forming on infected branches
Unfortunately, leaves and flowers typically don’t shed with fire blight, which makes it easier for the bacteria to spread to new branches. This is why pruning is highly recommended to combat fire blight.
While the browning of the flowers and leaves can sometimes be caused by other issues, such as under-watering, a telling sign of fire blight are the branches’ infamous 180º bend, or “shepherd’s crook”.
Additionally, some branches might form cankers and start to ooze sap from the bacteria. As a result, infected branches commonly turn a reddish-brown, or rust, color.
Treatments for Fire Blight
By far, the best practice to prevent and treat fire blight is to prune the diseased branches as soon as you see them. Keep in mind that pruning fire blight is done differently in the summer and winter (more on this later).
Additionally, you can get trees that are grafted onto a fire blight-resistance rootstock (such as Geneva rootstocks for apple trees). However, this won’t protect the scion, or upper part of the tree.
As a side-note: if you’re located in Washington, the best model to predict seasonal spikes of fire blight is CougarBlight.
Non-Organic Solutions
While I’m focusing more on the organic solutions in this post, I didn’t want to ignore the conventional solutions out there. So, I did my best to summarize them below and provided some specific information for you in case you’d like to research them further.
Antibiotic Sprays
Even though using antibiotics was effective in treating fire blight at one point, they were discontinued for use in orchards in 2014 due to harmful side effects. Because of them being discontinued, I won’t be covering them in much detail here.
However, I found many resources on antibiotics when doing research on fire blight. So, if you’d like to research this option more thoroughly, a simple Google search of “antibiotics fire blight” should give you plenty of information. For the current use of antibiotics on fire blight, make sure to check that the date of publication is current (after 2014).
Copper Fungicide Sprays
While copper fungicides are quite effective in treating many plant diseases, there are some potential side effects such as the disfiguring of leaves and fruit. Copper fungicides can be found at most garden stores or nurseries, and even on Amazon.
Biological Sprays
Some developments are being made with using certain strains of yeast to treat fire blight. A common example is Blossom Protect. These sprays work by using the yeast to compete for the same nutrients as the bacteria found in fire blight.
Additional products, such as Buffer Protect, change the pH on the surface of the plant, which helps the yeast grow faster than the bacteria, eventually outnumbering and overpowering them.
While these products have shown good early results, they are still in testing and not widely adopted or supported.
If you decide to treat fire blight with any of the above sprays, and you’d like more information, including which products to use and when to spray your trees, check out this resource by Washington State University.
Organic Solutions
Pruning
Pruning is the number 1 best thing you can do to limit the spread of fire blight. By pruning the diseased branches, you’re preventing the spread of fire blight to other branches that have yet to be infected.
Fire blight can easily be spread from external factors such as rain, insects, and especially—pruning. For this reason, it’s best to avoid pruning in wet weather.
Additionally, this is why cleaning your pruning shears after each cut is vital (something I often ignored when I was younger).
You can disinfect your pruning shears by dipping them in a 70% isopropyl alcohol solution after each prune.
While this might seem unnecessary, remember that fire blight is highly infectious and can be easily transmitted from branch to branch. Add to this that pruning exposes the tree’s cells—giving fire blight direct access to the tree’s immune system.
Pruning in the Summer
Because the fire blight bacteria commonly spread in temperatures above 70ºF, pruning the infected branches in the summer can be a bit tricky. The best approach in the summer is to prune the branches at least 12-18″ below where the diseased areas start.
Pruning in the Winter
In the winter, especially below 50ºF, fire blight is largely dormant. Because of this, you can cut the infected branches right before the start of the diseased site (unlike the summer months). Since you can remove the branches while the bacteria is dormant, pruning in the winter greatly limits the spread of fire blight.
However, it’s highly recommended to prune branches with fire blight whenever you see it, no matter the time of year.
Vinegar Spray
While organic solutions typically get a bad rep for not being as effective as chemicals, there are many anecdotes of them working for many organic orchard farmers. For example:
Alice and Dale Bautz of Great Falls report successfully using white vinegar to treat their fire blight-infected apple tree in 2010 at their former home in Dickinson, N.D… Bautz said they doused it before, during and after the blossom times, and paid particular attention to any wounds left from pruning.
Great Falls Tribune
If you’re interested in using vinegar to treat fire blight, I found a solution that has been shown to work:
- Add 6 cups of water and 4 cups of white vinegar to a 1-gallon garden sprayer
- Spray the tree from top to bottom (including the trunk, branches, leaves, blossoms, and fruit)
- Repeat again in 2 weeks
Remember to prune any infected branches before applying the vinegar solution. This will greatly reduce the spread of fire blight.
Essential Oil Spray
Even though I use peppermint essential oil in my homemade toothpaste, I have a hard time accepting other uses of them—especially when it comes to treatments. However, new research from Washington State University shows that using essential oils to treat fire blight has shown promising results.
Essential oils (e.g. from thyme, mint, cinnamon, oregano) have known antimicrobial activity. In one laboratory study active compounds from Origanum compactum (oregano family) and Thymus vulgaris (Thyme) were most effective (Kokoskova et al., 2011). In another study, Apium graveolens (celery seed) and Curcuma longa (turmeric) essential oils showed a reduction in Erwinia amylovora virulence (Akhlaghi et al.). These oils are rich in antioxidative phenolic compounds which are believed to be responsible for their antimicrobial activity (Chizzola et al., 2008).
Washington State University
In case you missed it, here are the essential oils that are recommended to treat fire blight:
- Oregano
- Thyme
- Celery Seed
- Turmeric
- Cinnamon
If you’re interested in recreating the promising treatment used in the studies, here are the measurements and directions that I was able to gather:
- Use a 23% solution of Thyme oil or 60% Cinnamon oil
- Apply when flowers reach 80% bloom, 1 day after 100% bloom, and when the petals start to fall
It’s important to hit fire blight with a solution before the blossoms open, as this is when they’re most vulnerable. Additionally, sprays after bloom and during petal fall are also recommended.
And this isn’t only for small orchards either. Essential oil products such as Thymegard, Thymox, and Cinnerate are available to commercial growers.
For more information using essential oils to treat fire blight, refer to the resource linked above.
Other Organic Sprays
Most other organic sprays contain citric acidic, which reportedly has mixed results. These sprays can also be easily washed off in the rain. However, after they remain on the leaves for at least 3 hours, it can help prevent and treat fire blight.
If you do decide to opt for a spray, remember that trees should be sprayed when they’re dormant and at the first sign of budding.
Fire Blight Resistant Apple Trees
| Most Resistant | Moderately Resistant | Least Resistant |
|---|---|---|
| Haralson | Honeycrisp | Cortland |
| Liberty | Zestar | Keepsake |
| Red Baron | – | McIntosh |
| SnowSweet | – | State Fair |
| Chestnut crab | – | Sweet Sixteen |
| Dolgo crab | – | Beacon |
| – | – | Fireside |
| – | – | Honeygold |
| – | – | Paulared |
| – | – | Wealthy |
If you’re interested in more information about fire blight resistant trees, check out this resource from the University of Minnesota.
My Recommendation
While I have yet to run into fire blight on my plants, I have no doubt I’ll see it in the future. If you would have asked me before I researched this post, I wouldn’t have thought essential oils would be an effective treatment. However, the recent research from Washington State University has shown otherwise.
From this research, I was able to gather enough information and anecdotes to confidently recommend organic solutions such as vinegar and essential oils.
Some final tips from me—make sure to avoid high-nitrogen fertilizers as this is shown to increase the growth of the fire blight bacteria. Also, mulch your plants to reduce the chance of soil bacteria splashing up onto the plant during watering (and to retain more water in the soil).
Remember, pruning is one of the best practices to use to manage the spread of fire blight. By pruning the infected branches, you’re limiting the bacteria from spreading to other branches. Just make sure to clean the pruning shears after each cut!
