Category Archives: Diseases

Identify Sudden Oak Death – Phytophthora ramorum

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The fungus behind sudden oak death or SOD, Phytophthora ramorum, is a new disease outbreak, first recorded in the early 1990′s.

In America, it has had a potent effect on their local Oaks (Quercus group). In Europe, it mainly attacks other unrelated plants, especially:

  • Rhodedendron.
  • Camellia.
  • Peiris.
  • Larch.
  • Ornamental viburnums like bodatense and tinus.

Native British oaks do not seem to be very susceptible.

Symptoms of Sudden Oak Death:
It can produce cankers that ooze a black liquid.

It can cause leaves to turn brown and die in a spreading patch from the edge.
You can read more about identifying it here.

Is Sudden Oak Death a major concern in the UK?
Yes.
According to this Telegraph article,  Mr Charlton Clark of the Forestry Commision described the area of Bristish trees that have recently been cut down & which will soon be cut down as being enough to fill 4,400 football pitches.
The estimate is that 4 million trees will be cut down.
Individual trees are are being removed in large numbers and Larch forests of up to 50, 000 trees are being cut down.

Why can you do about it?
If you spot it, you can report it to FERA, or the Forestry Commission if the trees are in a public wood.

Were you a Derby Day loser?

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We are getting a few enquiries about box blight from customers (and non-customers) who are worried that their box hedging might have contracted the dread disease.

When we are sent samples only about a quarter prove to be suffering from box blight which probably means that it is not as serious as people think – more “scare” than “there”. Where it is box blight, almost invariably the gardener concerned followed the old saw about never clipping your box hedge before Derby Day.

A lot of work has been going on researching the causes, treatments and outcomes of box blight.  We know that it is caused by two fungal organisms working in concert, that it spreads by infecting cuts on leaves and stems and that it is most likely to do so in warm, damp weather.

A lot flows from that:
1. Clip your box hedges so that the tops are NOT flat. Make them domed or pointed as this stops water resting in the leaves and creating a moist microclimate for fungal infections.

2. Try to clip them when it is COLD. At Highgrove they have had good results clipping their box at…..  Christmas. When it is cold and blight is sensibly sleeping. (It is at its most active in May-August, so it makes sense to clip outside these months if you can).

3. Spray your box hedging to prevent an outbreak.  Alternate copper fungicide and Scotts Roseclear3 and spray to 2-3 sprays a season.

4. We think box “grows out” of blight. There is a lot of evidence to that effect, but it need to lose a lot of top growth first.  The good news is that it will probably survive if you get blight.  The bad news is that box hedging grows so slowly that if you have blight in an established hedge it is going to look pretty grotty for quite a while.