Bay Leaf Tree (Laurus Nobilis) with severe scale

Question

I'm new to gardening as I have just bought my first house. I inherited a very large (about 6m tall) Bay tree that is severely sick. I took a sample to my local garden center and I was told that it is infested with Aphids/Scale (I think they mean Scale as I don't see anything that looks like an aphid) and they are producing honeydew, which has also caused the tree to be covered with a sooty mould. New leaves coming out are fine, but they soon succumb to the sickness. I am carrying out the garden center's recommendations but just wanted to ask here to see if they are in line with what you would do in my situation.

• I gave it a drench treatment of Thiamethoxam (following the directions for a 10m conifer) dissolved in 2 liters of water, as a systemic insecticide to hopefully kill the bugs feeding on it.

• Using a hand saw, I am now in the process of VERY aggressively pruning it back to basically just a pair of 3m high trunks with some main branches(as the tree is far too large anyway). I will then scrub the sooty mould off with soap and water.

• I also bought an oil insecticide which I plan to apply to any leaves that are left.

The problem is very severe and is infecting other trees in the neighbourhood, so it is important that I sort it out quickly. I think my Bay is the epicenter as apparently Bay trees are very susceptible to scale.

Do you have any other advice for how to treat a 6m Bay tree for severe scale? Is it OK to aggressively prune it back, as it is far too large? Is there anything else I should know about taking care of my Bay?

If it is important, I live in Cape Town, South Africa. We are in Spring, going in to Summer. The soil is sandy to loamy and we have already had most of our rain - our summers are dry and hot and our winters cold and wet.

EDIT: As requested, here are a few pics of my tree. Hope this is sufficient to identify the species, I'm not sure what to look at. I was told it is a Bay leaf tree (the kind you can use in curries). It is aromatic when you cut it. The tree has a silvery brown bark with some nodules and lots of scarring where the trunks have been damaged and pruned. The fresh leaves are oval-shaped and bright green, older leaves seem to be a dark green but there are no older parts that are not severely infected. At a guess I'd say the tree is between 30 and 100 years old (the houses here are about 100 years old) and the tree is well loved by my neighbours (and me) so I definitely want it to survive. On the advice of the garden center I have got stuck in with a saw but I'm postponing doing any more pruning until I hear more from this forum.

View from my roof (bamboo fence behind is 2m tall)

Another angle from roof

Close up of diseased leaf showing scale and sooty mould

Close up of fresh healthy new shoots showing one or two scale spots just starting

Trunks showing numerous scars from previous pruning and black sooty mould. There is a large wound on the one trunk that almost looks flaky and rotten on the inside.

Thanks for your interest and help!

Answer 1

The problem with a large tree like this is that trying to spray it requires professional equipment. Even with a pressurized sprayer you will get whatever you are spraying drifting onto to neighbors or public property.

In North America you would be opening yourself up for possible legal action by doing this. As you will not get complete coverage and scale that has not hatched yet may not be affected by the spray you will have to spray at least three times at five to seven day intervals.

My recommendations are:

• top dress with compost high in organic matter around the tree. Apply to a depth of one centimeter now and again in the fall, repeat yearly.
• apply a systemic using the application rates on the label
• thin the tree to make your job easier but there is no need to go at it with a saw

From here

When to lightly prune Prune in late winter or early spring. ...

How to lightly prune: No routine pruning necessary. Remove diseased, damaged, congested or crossing shoots. Shoots that are growing in unwanted directions can also be pruned out.

After pruning, mulch and feed.

What you want to do is a thinning pruning which is described here.

It took years for the tree to become badly infested with scale and it will take a few years to return it to health.

Edit: Ivan asks about re application of systemic pesticides. There are a number of different chemicals that are used so you are best to go with the recommendations on the label. As a rough rule, no more than once or twice a year. Keep in mind that by using a systemic you cannot use any of the leaves for cooking as they will contain trace quantities of the pesticide.

If you do a drastic pruning on a mature tree and take off sizable limbs you will get a lot of weakly attached sucker growth at the site of the cuts. This growth will be vigorous but after a few years can be so heavy that will break or be ripped off by wind. Not recommended unless you are willing to commit to pollarding

Answer 2

It is truly a beautiful plant! Get NEEM...this works very well and is pretty safe. Spray it at night so as not to hurt bees...just in case. Neem works very well with scale! You might have to do it every other week. Rent a sprayer or buy a cheapie 2gal pump sprayer. Spray the trunk, limbs and definitely under the leaves. This works very well and safely.

Answer 3

The lovely bay tree. I have noticed that my plants get infested with aphids etc when they are not in good health or are stressed. For some reason the aphids scale etc seem to arrive. I feed my plants with Seagro and also spray the plant with a seagro and water mix, as the plants get stronger the infestation goes. Before the seagro treatment, spray with sunlight liquid soap in a sprayer attached to your hose pipe. Its a mild mix of sunlight to water, about a teaspoon in a litre of water is what I usually use. Let it sit for just under an hour and then rinse off. This will kill off some of the infestation. You can also repeat this treatment say once a month, avoid spraying sunlight liquid too often as I find it can strip the gloss off the leaves a bit too much. Add compost to the soil regularly. The tree will heal itself when it's strong. Keep up regular feeding. Don't cut back too much it will weaken the tree. Enjoy your home and stunning tree xx