Hi @flo
Thanks for your comment on your Browning and shot-holed Hawthorn leaves. What you're describing with the brown spots and blackening leaves on your hawthorns is an incredibly common issue that nearly every hawthorn owner encounters at some point. The good news is that, whilst it looks alarming, it's rarely fatal to these absolutely bulletproof trees. It looks like a Hawthorn fungus/blight caused by entomosporium leaf spot.
Entomosporium Leaf Spot
Based on your description of brown spots followed by blackening and leaf drop, you're almost certainly dealing with Entomosporium leaf spot (also known as hawthorn leaf blight). This fungal disease is caused by Diplocarpon mespili and is particularly fond of the cool, wet conditions we've been experiencing lately.
The fungus starts as small reddish-brown spots on the leaves, which then develop grey centres with darker borders. As the disease progresses, the tissue between spots turns yellow, creating that characteristic "green island" effect where healthy leaf tissue remains green whilst everything else yellows. Eventually, the leaves blacken and drop prematurely.
The timing of your outbreak makes perfect sense.
This disease thrives in cool, moist weather and spreads through water splash from rainfall or irrigation. If you've had a particularly wet spell recently, that's your smoking gun. The fungus overwinters on fallen leaves and young twigs, then releases spores during spring rains that splash onto new growth. English hawthorns (Crataegus laevigata) are particularly susceptible to this issue, especially popular cultivars like 'Paul's Scarlet' and 'Crimson Cloud'.
Why Fungicides Aren't the Silver Bullet You Might Think
I know your first instinct might be to reach for the one of the garden centre sprays but here's why I rarely recommend jumping straight to fungicides for hawthorn leaf spot issues.
Firstly, most fungicides work as preventatives rather than cures. Once you can see the spots, the horse has already bolted, and spraying at this point is largely closing the stable door after the damage is done. The fungicides that are available to home gardeners (chlorothalonil, myclobutanil, and similar) need to be applied before infection occurs and maintained throughout the growing season with repeated applications.
More importantly, the environmental cost of fungicide use is increasingly understood to be significant. These chemicals don't just target your problem fungus; they affect beneficial microorganisms in the soil and on the leaf surface that actually help your plants maintain natural resistance. Research has shown that synthetic fungicides can disrupt the phyllosphere microbiome, reducing populations of beneficial endophytic fungi that naturally compete with pathogenic species. You're essentially carpet bombing your garden's ecosystem to deal with what is, in most cases, a temporary aesthetic issue.
There's also the growing concern about fungicide resistance. The intensive use of these chemicals has led to rapid evolution of resistant fungal strains, and we're seeing this become a serious agricultural problem worldwide. In your home garden, repeated fungicide use can actually make future outbreaks worse by selecting for resistant populations whilst decimating the beneficial microorganisms that provide natural disease suppression.
Why Hawthorns Are Absolute Survivors
The good news is that Hawthorns are amongst the toughest trees you can grow in the British climate. These trees have evolved over millennia to cope with exactly the sort of fungal pressures you're seeing. Whilst Entomosporium leaf spot can cause significant defoliation, it rarely causes long-term damage to healthy, established trees. Your hawthorns have been growing happily for two years, which means they've developed good root systems and are well-established in their location. The best treatment is to mulch now before winter and then give them a good spring clip next year in April.
https://youtu.be/_Dc3B2I7bu4
Hawthorns are renowned for their resilience and ability to bounce back from adversity. They're used to dealing with harsh conditions, from exposed moorland sites to urban pollution, and a bout of leaf spot is really quite minor in the grand scheme of things. The tree may look rough for a few weeks, but it will very likely produce a second flush of healthy growth once conditions become less favourable for the fungus. Many experienced gardeners have learned to simply accept that their hawthorns will have a "tatty period" each year and focus on supporting the tree's natural recovery mechanisms.
What You Can Actually Do to Help
Rather than reaching for chemicals, focus on cultural controls that address the root causes and support your trees' natural resilience. Start with garden hygiene: collect and dispose of all fallen leaves from around your hawthorns. This disrupts the fungal life cycle by eliminating the overwintering sites where the pathogen resides between seasons. Don't compost these leaves unless you've got a very hot composting system; instead, bag them up for council collection or burn them if local regulations permit.
Improve air circulation around your trees by pruning any overcrowded growth and ensuring there's adequate spacing between plants. Good airflow helps leaves dry quickly after rain, creating conditions less favourable for fungal development. If you're watering your hawthorns (which you probably shouldn't need to for established trees), water at soil level rather than overhead, and do it early in the day so any moisture on foliage evaporates quickly.
Consider your soil conditions and nutrition. Trees under stress are more susceptible to disease, so ensure your hawthorns aren't struggling with waterlogged or extremely poor soil. A light application of general-purpose fertiliser in spring can help support vigorous growth, but avoid high-nitrogen feeds which promote soft, succulent growth that's more vulnerable to infection. Hawthorns actually prefer slightly lean conditions and can become more disease-prone when overfed.
https://youtu.be/5BhGtCjT2TQ
Finally, be patient and observe. Many gardeners are surprised to discover that their "diseased" hawthorns put on a strong second flush of healthy growth later in the season, once the initial fungal pressure subsides. Your trees may look decidedly sorry for themselves right now, but give them time to show you their remarkable powers of recovery.
Whilst your hawthorn leaf spot looks dramatic and concerning, it's really more of a cosmetic issue than a life-threatening crisis. These magnificent trees have been dealing with fungal challenges for far longer than we've had chemical fungicides, and they're remarkably good at it when we give them the chance to do what they do best: survive and thrive in the British landscape!
All the best
Lee Garden Ninja
Hi @flo
Thanks for your comment on your Browning and shot-holed Hawthorn leaves. What you're describing with the brown spots and blackening leaves on your hawthorns is an incredibly common issue that nearly every hawthorn owner encounters at some point. The good news is that, whilst it looks alarming, it's rarely fatal to these absolutely bulletproof trees. It looks like a Hawthorn fungus/blight caused by entomosporium leaf spot.
Entomosporium Leaf Spot
Based on your description of brown spots followed by blackening and leaf drop, you're almost certainly dealing with Entomosporium leaf spot (also known as hawthorn leaf blight). This fungal disease is caused by Diplocarpon mespili and is particularly fond of the cool, wet conditions we've been experiencing lately.
The fungus starts as small reddish-brown spots on the leaves, which then develop grey centres with darker borders. As the disease progresses, the tissue between spots turns yellow, creating that characteristic "green island" effect where healthy leaf tissue remains green whilst everything else yellows. Eventually, the leaves blacken and drop prematurely.
The timing of your outbreak makes perfect sense.
This disease thrives in cool, moist weather and spreads through water splash from rainfall or irrigation. If you've had a particularly wet spell recently, that's your smoking gun. The fungus overwinters on fallen leaves and young twigs, then releases spores during spring rains that splash onto new growth. English hawthorns (Crataegus laevigata) are particularly susceptible to this issue, especially popular cultivars like 'Paul's Scarlet' and 'Crimson Cloud'.
Why Fungicides Aren't the Silver Bullet You Might Think
I know your first instinct might be to reach for the one of the garden centre sprays but here's why I rarely recommend jumping straight to fungicides for hawthorn leaf spot issues.
Firstly, most fungicides work as preventatives rather than cures. Once you can see the spots, the horse has already bolted, and spraying at this point is largely closing the stable door after the damage is done. The fungicides that are available to home gardeners (chlorothalonil, myclobutanil, and similar) need to be applied before infection occurs and maintained throughout the growing season with repeated applications.
More importantly, the environmental cost of fungicide use is increasingly understood to be significant. These chemicals don't just target your problem fungus; they affect beneficial microorganisms in the soil and on the leaf surface that actually help your plants maintain natural resistance. Research has shown that synthetic fungicides can disrupt the phyllosphere microbiome, reducing populations of beneficial endophytic fungi that naturally compete with pathogenic species. You're essentially carpet bombing your garden's ecosystem to deal with what is, in most cases, a temporary aesthetic issue.
There's also the growing concern about fungicide resistance. The intensive use of these chemicals has led to rapid evolution of resistant fungal strains, and we're seeing this become a serious agricultural problem worldwide. In your home garden, repeated fungicide use can actually make future outbreaks worse by selecting for resistant populations whilst decimating the beneficial microorganisms that provide natural disease suppression.
Why Hawthorns Are Absolute Survivors
The good news is that Hawthorns are amongst the toughest trees you can grow in the British climate. These trees have evolved over millennia to cope with exactly the sort of fungal pressures you're seeing. Whilst Entomosporium leaf spot can cause significant defoliation, it rarely causes long-term damage to healthy, established trees. Your hawthorns have been growing happily for two years, which means they've developed good root systems and are well-established in their location. The best treatment is to mulch now before winter and then give them a good spring clip next year in April.
Hawthorns are renowned for their resilience and ability to bounce back from adversity. They're used to dealing with harsh conditions, from exposed moorland sites to urban pollution, and a bout of leaf spot is really quite minor in the grand scheme of things. The tree may look rough for a few weeks, but it will very likely produce a second flush of healthy growth once conditions become less favourable for the fungus. Many experienced gardeners have learned to simply accept that their hawthorns will have a "tatty period" each year and focus on supporting the tree's natural recovery mechanisms.
What You Can Actually Do to Help
Rather than reaching for chemicals, focus on cultural controls that address the root causes and support your trees' natural resilience. Start with garden hygiene: collect and dispose of all fallen leaves from around your hawthorns. This disrupts the fungal life cycle by eliminating the overwintering sites where the pathogen resides between seasons. Don't compost these leaves unless you've got a very hot composting system; instead, bag them up for council collection or burn them if local regulations permit.
Improve air circulation around your trees by pruning any overcrowded growth and ensuring there's adequate spacing between plants. Good airflow helps leaves dry quickly after rain, creating conditions less favourable for fungal development. If you're watering your hawthorns (which you probably shouldn't need to for established trees), water at soil level rather than overhead, and do it early in the day so any moisture on foliage evaporates quickly.
Consider your soil conditions and nutrition. Trees under stress are more susceptible to disease, so ensure your hawthorns aren't struggling with waterlogged or extremely poor soil. A light application of general-purpose fertiliser in spring can help support vigorous growth, but avoid high-nitrogen feeds which promote soft, succulent growth that's more vulnerable to infection. Hawthorns actually prefer slightly lean conditions and can become more disease-prone when overfed.
Finally, be patient and observe. Many gardeners are surprised to discover that their "diseased" hawthorns put on a strong second flush of healthy growth later in the season, once the initial fungal pressure subsides. Your trees may look decidedly sorry for themselves right now, but give them time to show you their remarkable powers of recovery.
Whilst your hawthorn leaf spot looks dramatic and concerning, it's really more of a cosmetic issue than a life-threatening crisis. These magnificent trees have been dealing with fungal challenges for far longer than we've had chemical fungicides, and they're remarkably good at it when we give them the chance to do what they do best: survive and thrive in the British landscape!
All the best
Lee Garden Ninja
Lee Burkhill: Award Winning Designer & BBC 1's Garden Rescue Presenters Official Blog
