Tag: Fruit tree

Are they burr knots or crown galls on my apple tree?

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That was my big gardening question this week. I even put the question out on the garden Twittersphere, which is usually a very helpful and knowledgeable place.

I didn’t get an answer, which suggests it’s not a common problem (lucky me!).

Basically, I have some rather unsightly, tumour-like growths sprouting from the trunk of my 8-year-old Braeburn apple tree.

Burr knot or crown gall near base of apple tree?
Unsightly growths on base of apple tree, with small root-like projections

A Google search narrowed this down to one of two possibilities: burr knots or crown galls.

Burr knots

Burr knots are not caused by a disease. They are root initials growing in the wrong place. They are most common on woody plants grown on root stock, like my apple tree. There seems to be several possible causes – low light, high humidity and dry soil – and my tree ticks all those boxes.

Burr knot on apple tree

Burr knots cause several problems.

  • They weaken the affected branch or trunk, making it more prone to breaking in high winds or from the weight of apples.
  • They provide an entry point for pests and diseases, particularly woolly aphid.
  • If a lot of them join up, they can damage the living tissue of the plant (phloem) that conducts nutrients around the tree.

Crown galls

Crown galls are caused by a bacteria in the soil that gets into the tree through wounds in the bark: for example, from pruning or frost damage. The bacterial disease causes knobbly tumour-like growths, usually around the base of the plant, but elsewhere as well. They usually look like warts early in development.

Crown galls can affect the growth of the tree, and the bacteria can be spread to other plants on contaminated gardening tools. The bacteria also persists in the soil for a long time.

So … burr knots or crown galls?

I’m still not completely sure, but having scrolled through dozens of pictures and websites I’m veering towards burr knots, as they look like small root projections rather than ‘knobbles’ or ‘warts’.

Burr knots on trunk of apple tree

How to treat burr knots

So the bad news is, there’s not a lot I can do. Cutting them out risks damaging the tree even more and introducing canker.

Prevention rather than cure. I can try to prevent more from forming though. I’ve removed a couple of branches so that more light can penetrate and I will give the tree more water this summer. We’ve had two very dry summers and the tree is in a corner of the garden on a mound of clay-based soil, so I expect it has dried out too much at times.

To be honest, it has never produced many apples, so it may be on borrowed time anyway!

How to treat crown galls

Because the bacteria can spread to other plants, the tree and all its roots should be removed and destroyed, and you should wait a couple of years before planting any other susceptible plants in that soil.

So, I really hope mine are burr knots and not crown galls. To be on the safe side, I will make sure I disinfect my tools after working in that area.

If anyone can tell for sure from my pictures, please let me know!!

Late fruit tree pruning

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The clocks have gone forward and it’s officially Spring, but you’d never know it given the current weather, and neither does my apple or pear tree! Both are in bud but neither has produced any leaves yet, so I figured I could get away with some late ‘winter’ pruning this week.

Apple tree in winter bud

‘Winter’ apple tree – lots of buds but no leaves yet

Conventional wisdom advises pruning when the tree is dormant, between leaf fall and bud burst (late November to early March), so I’m pushing it a bit, but better to do it now than not at all.

5 simple rules for pruning fruit trees

If you’re not used to it, pruning can be a scary concept, especially when you start reading terms such as renewal pruning and spur bearers, so I’ve condensed it down to 5 easy-to-remember rules.

  1. Remove any dead, damaged or diseased branches.
  2. Remove any branches that are crossing or rubbing against each other.
  3. Remove any branches that are heading for the centre of the tree.
  4. Shorten the previous year’s growth on each main branch by about a third.
  5. Remove any young lateral branches that are causing overcrowding.

Remove any crossing or rubbing branches

Remove any crossing or rubbing branches

Use a sharp pruning saw or secateurs and cut just above a bud that is facing in the required direction (ideally you want your tree to keep branching outwards to avoid congestion in the middle).

Above all, prune the tree to the size and shape that fits your garden. It’s no good having a heavy cropping apple tree if it casts a shade over everything else you want to grow. I’ve had to hack a fair bit off my pear tree this year, as it was getting top heavy and leaning over the drive. I probably won’t get as many pears, but people will be able to walk to the front door!

Follow up with a good mulch and wait for that wonderful explosion of blossom. It’s coming …. honest!!