How to deal with sudden tree death
Sudden tree death is a particular tragedy for small and middle-sized gardens. We only have a few trees. And each one is special.
We have a smokebush (Cotinus coggygria ‘Grace’) which has grown to a height and spread of around 7 metres (about 25ft).
Its glorious red foliage is the main focus in the garden, especially in autumn when it changes from glowing copper to burnished gold almost in front of our eyes. It shields us from nearby windows (for more about trees for privacy, see here.)
This year has seen a long, cold, wet spring followed by a hot, dry summer. In the middle of August the Cotinus suddenly turned brown on one side. All the leaves off one main branch had died.
Step one – try Google
I searched for ‘Sudden tree death’ and ‘Cotinus coggygria dieback.’ The specific query was more helpful. Second from top of the page was the RHS advice on Verticillium wilt.
The symptoms matched. There was also a list of other susceptible plants, including elder and rose. Two years ago a black elder and a Rosa ‘Rosarie de la Hay’ both looked dead.
We cut back the black elder and it has since revived. It seemed likely they were both affected by Verticillium wilt.
Other trees have also died in this garden. We thought honey fungus was to blame, although we couldn’t see or smell it. It’s possible that verticillium wilt was the culprit, not honey fungus all along.
Step two – phone a friend (one who knows more than you do)
Posy looked at the tree and spotted that all the dead leaves were attached to one branch. She advised cutting it off. She also agreed that the symptoms looked like verticillium wilt.
The tree looked more graceful, and appeared completely healthy. Phew. A lucky escape.
However, a month later we returned from a long weekend to find leaves browning and curling up in another section of the tree.
Matt Jackson is a garden consultant, and works on large estates (as well as smaller gardens). Some have lots of trees, so he’s accustomed to peering at bark and rootling around roots. ‘But on a large estate, a dying tree either isn’t a problem – we just take it down. Unless it’s a very big problem because it may have a notifiable disease that affects a whole swathe of trees.’
In a middle-sized garden, a dying tree is quite a middle-sized problem because the tree will leave a big hole when it’s gone. And it takes years to grow a tree to seven metres high.
On the other hand, the middle-sized gardener often sees a hole as an opportunity.
Matt recommended that I scrape away a bit of bark to see what was going on underneath. ‘If you can see green, then the tree is probably fundamentally healthy,’ he said.
I can see green, but I can also see the striations of fungal infection.
Step three – post it on social media.
I posted ‘Has my smoke bush got verticillium wilt?’ on Twitter, along with photographs.
Nobody sniggered. A few people got back to me and said they agreed it was probably likely.
Step four – join the RHS and send a sample
The RHS run a personalised advisory service for members. You can send a sample of material, plus photographs.
I went out to snip some dead leaves off, and also noticed that there were tiny, flea-like insects on the leaves.
It’s all been bundled into a bag and is ready to post. However, if it is verticillium wilt, it’s not treatable and will stay in the soil forever, according to the RHS.
You can also consult the Forestry Commission‘s diagnostic and advisory service, Forest Research. They also take postal samples, but charges apply.
Step five – consult a tree surgeon
The problem is that not all people who call themselves tree surgeons are qualified to diagnose diseases.
The Arboricultural Association has a Find-a-professional service here. However the nearest one to us was around 40 minutes drive away, and that makes visits expensive. Qualified tree surgeons (quite rightly) charge several hundred pounds a day.
They can do things like improve the soil and nutrition around the tree, but it’s not a guaranteed cure. You could spend a few hundred pounds and still lose the tree.
There are lots of people who live nearer and who call themselves ‘tree surgeons.’ Some I would describe as ‘Chain-Saw Man’, whose only aim is to cut trees down. See the difference between arborist, tree surgeon and chain saw man here.
Step six – plan for the worst and hope for the best
We have decided to prune the tree in the winter, and also to plant another tree nearby. It must be one that is resistant to both honey fungus and verticillium wilt. Matt recommends Liquidambar styraciflua, which is resistant to verticillium wilt and rarely attacked by honey fungus.
We’ll mulch the area. When spring comes we will also look into giving all our trees some extra nutrition.
When pruning a tree back, then always think about the shape. Even if you’re having to cut away dead branches, it’s worth thinking about pruning it for both light and privacy.
Update in 2021…
The following spring the cotinus grew back well. But we had another dry summer, so another chunk died.
We have since slowly cut it back every autumn, bringing it back down to the size of a large shrub rather than a small tree. The summer of 2021 was relatively wet, and the tree shows no signs of dieback.
So if you think your tree is suffering from verticillium wilt, don’t rush to cut it down. It’s very difficult to get viruses and funghi out of the soil permanently, so your only option is to plant trees and shrubs that don’t suffer from those problems.
You can see how healthy it looked in 2018 in this post on the best trees for autumn colour.
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