I’ve seen some cases of pear trees getting black leaves but I wasn’t too familiar with what exactly causes it. So, I did some research to find out. Here’s what I found.
Pear trees get black leaves from diseases including fire blight, fabraea leaf spot, and pear scab. While fire blight is a bacterial disease, leaf spot and scab are fungal. All three diseases are highly contagious and difficult to get rid of, with the best method being prevention. Pruning and sprays may help.
So, while pear trees get black leaves from several causes, how can we tell which issue is causing it, and how can we fix it? Let’s take a closer look.
3 Reasons Why Pear Trees Get Black Leaves
1. 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, blacking, and disfiguring of the leaves and fruit, sometimes killing the tree.
This disease spreads most often in the springtime when it’s warm and wet (spreading the fastest when the temperature is above 70ºF). However, during the winter, fire blight is dormant. This is why providing preventative treatment to the trees during the winter is important in handling this disease.
The bad news is that fire blight is the most common pear tree disease, and there is no cure for it.
The good news is some treatments prevent and slow the spread of fire blight (more on these later). With these, fire blight is manageable and should have little to no further impact on your trees.
To see a fire blight map of the US, check out this map on uspest.org.
Also, to read more about this disease, feel free to visit my other post: Fire Blight Treatment: Non-Organic & Organic Solutions.
2. Fabraea Leaf Spot (Also Called Leaf Blight or Black Spot)
Fabraea leaf spot (Fabraea maculata) is a fungal disease that causes pinpoint brown and black spots on pear tree leaves, fruit, and branches. Usually, this disease is active in late May and early June, and excessive infection can lead to yellow and dropping leaves. Pruning while the tree is dormant is best.
Like the other fungal diseases on this list, warm, wet, and windy weather commonly blow around these fungal spores, spreading the disease to other leaves and trees.
3. Pear Scab
Pear scab (Venturia pirina) is similar to apple scab, causing circular, velvety olive-black spots on the tree’s leaves, fruit, and branches. Over time, the lesions turn grey and cracked. Pear scab is most common from March to late June. This disease can be managed with pruning and some sprays.
One effective method of managing pear scab is companion planting. Specifically, interplanting chives with pear and apple trees has been shown to help prevent scab (source).
For more information about pear tree companion plants, including how they can help prevent pests and diseases, check out my other post: The 10 Best Companion Plants for Pear Trees.
How to Treat Black Leaves on Pear Trees
Whether your pear tree has a bacterial or fungal disease, the treatments are largely the same.
Treatment for these diseases include the following methods:
Let’s break each of these down a bit.
As you might have guessed, prevention is the best way to minimize and stop plant diseases. Prevention is more proactive than other approaches and includes using proper gardening practices such as not spraying the leaves with water, using naturally resistant trees, and selectively breeding pear trees for more resistance.
For example, when watering, avoid spraying the leaves as this spreads the infection from leaf to leaf. This also causes the leaves to die and fall off the tree sooner. Instead, water the soil and minimize splashing.
You can also use pear tree varieties that are naturally resistant to the disease. While no pear tree varieties are completely resistant to fire blight, some have a slight to moderate resistance:
- Harrow Crisp
- Harrow Gold
- Harrow Delight
- Harrow Sweet
- Harvest Queen
- Old Home
- Starking Delicious
Pruning is one of the best practices to limit the spread of most diseases. By pruning the diseased branches, you’re preventing the spread of the disease to other branches that have yet to be infected.
Many diseases can easily 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 cleaning pruning shears might seem unnecessary, remember that these diseases are highly infectious and can be easily transmitted from branch to branch. Add to this that pruning exposes the tree’s cells—giving these diseases direct access to the tree’s immune system.
Pruning in the Summer
Because plant diseases 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 blackened or diseased areas start.
Pruning in the Winter
In the winter, especially below 50ºF, many diseases are largely dormant. Because of this, you can cut the infected branches right before the start of the diseased site (unlike the 12-18″ suggested in the summer months). Since you can remove the branches while the disease is dormant, pruning in the winter greatly limits the spread.
However, especially with fire blight, it’s highly recommended to prune diseased branches whenever you see it, no matter the time of year.
Keep in mind, that if you’re not a fan of pruning, there are other effective options (more on these later).
Some copper fungicides are effective in dealing with certain pear tree diseases. When applying copper fungicides, all parts of the tree should be covered in the spray and used until runoff. Instructions vary depending on the product, so refer to the label for more specific information.
While chemical sprays can be useful at times, many have been discontinued due to safety issues or ruled as ineffective. Because of this, many gardeners are looking for other, more natural options.
The best organic solutions to treat pear tree diseases are vinegar and essential oils. For example, 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 a few times per year.
Let’s take a look at how these solutions work for many gardeners.
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 pear tree diseases, I found a solution that’s 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 disease.
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).
S.Tianna DuPont, WSU Extension Specialist, Assistant Professor. Washington State University Extension.
In case you missed it, here are the essential oils that are recommended to treat fire blight:
- Celery Seed
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 most diseases with a solution before the blossoms open, as this is when the tree is at its 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 and other pear tree diseases, 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 pear tree diseases.
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.
Even though chemical sprays are an easy way out, like all easy and convenient things, there are usually long-term costs. Namely to the plants, soil, and surrounding beneficial life. Before using conventional sprays, weigh the pros and cons and consider using organic or permaculture-based treatments first.
Along with the above sprays, here are some of the most effective organic methods that I’ve found to manage black leaves on pear trees and other plant diseases:
- Minimize tree stress (use best practices such as deep watering, composting, and mulching)
- Homemade whey spray
- STUN method
If you’re interested, I’m adding two videos below so you can learn more about organically managing diseases on fruit trees.
Homemade Whey Spray
Stefan Sobkowiak – The Permaculture Orchard has a great video on a safe, homemade, and most importantly—effective fungicide (hint: the secret ingredient is whey).
Mark Shepard, on his 100+ acre farm, uses a method called STUN (sheer total utter neglect) and it works wonders for him. He uses no chemical fertilizers, sprays, or any other dependencies. Through the struggle, his fruit trees become stronger and his job gets easier.
Check out the below video for more about Mark Shepard and STUN.