Brown or black discoloration on a pear tree’s foliage – certainly they spoil its good looks, but it tells you something about the tree’s health as well. It’s extremely important to make the diagnosis because in many cases, if left untreated, the tree will die – and worse, the problem can spread to more trees on your property. A little bit of action now will save you a lot later on.
It’s not at all uncommon to see pear trees develop clumps of shriveling, dry-looking leaves that turn brown or black or become dotted with rust-colored spots. So what causes this?
Brown or black leaves on a pear tree are usually caused by the bacterial infection fire blight, which must be properly managed to prevent spread to the rest of the tree. Other factors causing leaf browning include frost, lack of water and fungal infections, such as pear rust and fabraea leaf spot.
I’ll hope to explain the issues in an understandable way, so you’ll be able to diagnose the problem with your tree and know what to do! Being a pear-tree owner I’ve experienced this issue firsthand, and I’d love to help.
What is fire blight?
Fire blight is caused by the bacteria Erwinia amylovora and so-called because it’ll look as if part of your tree has been scorched by flame. Usually a clump of leaves, often together on a small branch, will be shriveled and brown or black; the branch itself may have darkish blotchy patches and the wood inside is stained a brownish color.
It affects many tree species (such as apple, hawthorn, cherry, mountain ash, cotoneaster) but pear trees are particularly prone. It’s an important commercial concern worldwide for pear and apple growers and has throughout many years spread to most countries worldwide (Australia has, with great effort, been able to keep it out of their country’s pear trees to date).
The infection is spread by insects (such as ants and bees) from tree to tree and from one part of the tree to another. It usually enters via flowers, and will destroy fruit, leaf and branch and eventually tree itself, as it spreads down towards the roots – this spreading can go as quickly as 2 inches per day.
Fire blight overwinters in ‘cankers’ – sunken blotches in the tree’s bark, often looking darker in color than the rest of the branch or trunk. In spring, when the temperature goes about 65°F (18°C), if there’s enough rain or humidity, the infection becomes active again and the browning and shriveling of flowers, leaves and twigs will begin. So it follows that fire blight is less common in cooler regions. In the UK for example, there isn’t as big a problem with fire blight as in warmer parts of the US.
What to do if you think your pear tree has fire blight
Dead and dying tree parts should always be pruned off of trees anyway, but with fire blight, if you do this wrong you’ll make the tree worse. The disease can’t be cured, but it can be cut off and controlled. It’s not too difficult if you know how.
There are three big principles of pruning fireblight:
- you’ve can’t just prune off the obviously diseased part – you’ve got to take off extra length on that branch as well, even if this means some other healthy-looking offshoots. How much depends on the time of year – see below. To assess how far the disease is spread, LOOK CAREFULLY at the branches that the brown leaves are on (not just the leaves themselves)… if the branch appears discolored, consider it diseased.
- Between every cut, you’ve got to sterilize your pruning shears. This is an infection that readily spreads. Use rubbing alcohol or alcohol-based hand sanitizer and make sure you work it into the cutting area, then allow them to dry. Household bleach (diluted with water to one-tenth its concentration) is an alternative. Hand sanitizer’s a good choice because you can sanitize your hands between cuts, at the same time.
- Any part that’s pruned off must be either burned or put into the regular trash. It must not be allowed to blow away, or be composted – it can and will infect other trees.
What time of year should I prune off fire blight?
|Time of year
|– Easier to identify infected areas from brown leaves and flowers.
– No waiting – you’re actively combatting the infection during its spreading stage
– Need to cut off more healthy shoot as well – an extra 12 inches past the infected area
– Lots of leaf debris generated – this must all be carefully picked up and put in the trash, or burned before it infects other trees
|– The disease is essentially dormant at this time, so you may be able to prune off less extra (healthy) branch – 6 to 8 inches may be adequate.
|You might miss some branches that have minor infection, particularly if your tree has lost its leaves for the winter – cankers are harder to identify than afflicted leaves, particularly on small branches
Some arborists will suggest that if fire blight has spread to branches that are more than an inch thick, you should cut twice as far into healthy tissue (so an extra 2 feet in summer).
What if the cankers are in the tree’s trunk? The tree by this stage is at risk of death from fire blight, which can soon spread to the roots, but you can scrape the cankers off with a sharp knife. You should make sure that the full thickness of the bark is removed and that you also remove a small border of healthy-looking bark, to ensure you fully excise the infected part.
The tree’s survival chances depend on how much of the trunk’s circumference you need to cut out. Check out this post for an insight into how much bark injury a tree can take and still survive and thrive.
Other fire blight treatments
Fire blight is susceptible to a number of antibiotic treatments including streptomycin and oxytetracycline, and copper solutions can be used. HOWEVER… there’s no substitute for proper pruning practices, and I would leave these treatments to a trained arborist.
Streptomycin in particular has lost some of its effectiveness against fire blight, because of improper and excessive use that has allowed the bacteria to develop resistance against it.
Most commercially available treatments for fire blight are non-specific to the disease, and won’t be effective enough. Time spent using these treatments will be time lost, so if you aren’t sure you can prune out fire blight, consult an arborist.
Brown spots on pear tree leaves
If it’s spots on the leaves of your pear tree (rather than leaves that are mostly or entirely brown) you’re usually dealing with a fungal infection. Thankfully, these aren’t lethal like fire blight, but they can still affect both flower and fruit production, which are two of the most important things about owning a pear tree.
Pear rust – Gymnosporangium sabinae
These orange-brown spots can have horn or string-like growths growing out of them called telia. Suspect this one if you have any juniper nearby – typically, this infection winters in juniper, and spreads to pear in spring and summer, enlarging until fall.
This infection isn’t lethal and doesn’t normally affect its growth and overall vigor much, but the brown blotches will affect the appearance of the tree significantly.
If you have any juniper trees on your property, go and see if you can see any similar orange lesions on them. I should mention though – it can spread from junipers that are hundreds of yards away or even further (the fungal spores are spread by wind), so not having juniper trees on your property doesn’t rule out this diagnosis.
Fungicidal treatments need to be applied early in the growing season before the spots appear. Most commercially available fungal sprays, such as those containing tebuconazole or triticonazole, will have a controlling effect if sprayed in accordance with the manufacturer’s instructions. However, I don’t use sprays yourself if you’re hoping to eat the pear fruit from your tree. In that instance, you should consult a trained arborist in your area.
Here’s a great summary video about pear rust that I found on YouTube.
Fabraea Leaf Spot, aka pear leaf blight – Diplocarpon mespili
This fungal infection is different from pear rust in that
- It requires no separate winter host tree, but instead winters in cankers, a bit like fire blight
- The leaf spots are smaller, dark brown or purplish-black instead of rust colored, and they don’t have ‘telia’ growing out of them
- It can cause more extensive damage to the tree, making fruit inedible and causing considerable leaf loss
If you think your tree has fabraea leaf spot, the important first step is to prune away diseased plant parts with secateurs that are sterilized after each cut to prevent spread to other parts of the tree, then careful disposal of what’s been pruned off – follow the instructions as above for fire blight.
Given the effect it can have on fruit, this infection’s a big issue for commercial pear growers. In agriculture, various fungicides are used to control the infection, but it’s a different matter when you’re using these at home. If your tree is only mildly affected and those parts can’t simply be pruned off (as for fire blight) I would consult a local arborist about chemical control.
Browning, blackening or spotty pear tree leaves – a quick reference table
|Frabraea leaf spot aka pear leaf blight
|Type of infection
|Withered brown or black leaves, dark ‘cankers’ on bark
|Rust-colored spots or blotches on leaves with ‘telia’ growing out of them
|Numerous brown-black or purplish tiny dots on leaves
|Risk to tree
|Eventual death via spread throughout the tree
|Mostly a cosmetic concern
|Can cause significant leaf loss and ruin fruit
|Pruning with a sterilized instrument, proper disposal of removed parts to prevent spread.
Antibiotics for experts
|Antifungal spray treatment
|Pruning with a sterilized instrument, proper disposal of removed parts to prevent spread.
Antifungal treatment for experts
Other causes of pear tree leaves going brown or black
If after reading through the above you aren’t convinced that your pear tree has an infection… yes, there are other causes to consider.
The default color change for an unhealthy pear tree’s leaves is towards brown or yellow. There are certainly other factors (apart from the infectious diseases discussed above) that can cause this type of unsightly foliage to appear:
Under or overwatering
Pear trees, particularly when younger, need irrigation during dry periods. Lack of water tends to show up early in the health of leaves, which can look withered, dry or curled, and exhibit color change. Similarly, waterlogged soil deprives roots of air, essentially drowning the tree and causing signs of stress in the foliage.
During dry spells, water your pear tree once weekly. Ideally, the irrigation should be directed to the whole root area (which will, very approximately, mirror the canopy of the tree above ground). Realistically this will take around 30 minutes with a sprinkler – longer if it’s particularly hot and dry, or your soil is sandy. It’s probably better to give the tree a heavy soak once a week than a light watering every day – you’re trying to get water deep into the soil, not just the first couple of inches.
If you’re not sure whether you need to water your pear tree, it’s easy to check – just dig your finger 1-2 inches into the soil. If it feels dry and/or the soil doesn’t stick to your finger – time to water.
Cold weather damage to pear tree leaves
Pear trees are relatively hardy, meaning they can survive cold temperatures. In the US, most will grow in areas as cold as USDA hardiness zone 4 (where the average annual minimum winter temperature is -30 to -25 °F (-34.4 to -31.7 °C). Here’s a reference map from the USDA’s website where you can check your own hardiness region. Frosts, particularly those that occur in late spring, can cause freezing at the tips of the leaves, resulting in brown edges that are curled or shriveled. These leaves don’t need to be removed unless they’re completely dead (it’s a good rule of thumb to prune off any diseased or dead tissue). Just make sure it isn’t fire blight first! It usually shows up on leaves during an increase in temperature (and humidity), rather than a decrease!
Wind damage to pear tree leaves
Young pear tree leaves can be quite sensitive to high winds, particularly in spring, and can result in browning leaves which may even die and drop off. This is likely to resolve when the tree’s older. Again, your priority is to make sure it isn’t fire blight.
I hope this post has been helpful. Please check out my other articles, all about gardening, the hands-on way!
Ninjatacoshell, CC BY-SA 3.0 https://creativecommons.org/licenses/by-sa/3.0, via Wikimedia Commons
Scot Nelson, CC0, via Wikimedia Commons