7

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)

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

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 diseased leaf showing scale and sooty mould

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

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.

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!

  • 1
    This is a very aggressive treatment plan. Cutting back the foliage is not something I would do at the same time as a systemic. We need a photo or two to identify the species and be more accurate. – kevinsky Nov 17 '14 at 12:10
  • Thanks kevinsky. Perhaps I should then wait a bit for the systemic to do its thing before I cut it back any more? It is very big and bushy and needs pruning anyway as it is blocking all the light in my yard - I applied the systemic yesterday and lopped off about 10% of the foliage - how long should I wait before pruning the rest? I will post a photo of it tomorrow. – Ivan Nov 17 '14 at 13:57
  • 1
    I have edited the post with some photos and a bit of a a description. Let me know if you need any more info! – Ivan Nov 17 '14 at 17:40
  • @kevinsky I won't go as far as to recommend it, but this is how my inlaw got rid of a huge scale infestation. He just cut all branches off. After that, new shoots came out and the tree is back to normal. Bay leaf seems to be a very vigorous plant. – user10810 May 23 '16 at 8:50
  • 1
    @jbcreix in the end, that is what I did. Couldn't get rid of the scale and figured if I kill it, then the decision would be made. Tree growing back quickly, beautifully and healthy! Remains to be seen whether the sucker growth will stand up to the wind but so far, so good. – Ivan May 23 '16 at 8:54
5

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

  • Arg... years? That's a pity. Thanks for your help, I'm going to follow your advice. Spraying isn't really an option because of the size and location. Will accept yours as an answer, but just one last question - can I reapply a systemic and how often can I do this? – Ivan Nov 18 '14 at 12:03
  • What would happen if I cut off ALL of the diseased foliage and allowed the tree to grow back from the main trunks, treating leaves as they emerge? The scale is infecting other plants in the area and I don't have years to sort the problem out. – Ivan Nov 18 '14 at 15:27
  • 1
    After pruning, make sure that you collect all the debris and dispose of it properly - or burn it. Also a pressure washer can be an effective tool in your arsenal for managing scale as long as you are careful not to damage the bark and foliage with too much pressure. – That Idiot Jan 6 '15 at 12:29
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.

  • Thanks! I think it will be beautiful when it's healthy. I think Neem is a similar thing to what I got, I don't have the container with me but I will check when I get home. It is an oil pesticide that suffocates the scale. Problem is, the tree is huge and very difficult to get at (especially if I have to do it twice a month). Would you recommend chopping off say half the foliage then spraying the rest? – Ivan Nov 18 '14 at 7:23
  • Pruning will help the tree if it is done correctly. With sterilized by-pass pruners or a good tree saw, cut branches that aren't healthy, that aim into the center of the tree, branches that have a diameter far smaller than the main branch it is attached to, branches that don't receive enough light to be productive. Use alcohol to clean pruners, cut branches off at their base! Don't do more than 1/3 of the tree and probably even less. This will help when you spray. A dormant oil is ok, but Neem is a bit different. Find out what a professional would charge... – stormy Nov 18 '14 at 23:13
  • Thank you for mentioning bees. Too often people apply "organic" pesticides without realizing that these are often just as toxic to non-target species. – That Idiot Jan 6 '15 at 12:27
  • Us humans depend on bees! When they go, we go very soon afterwards. Very happy that you care!! Let us know how your tree is thriving. We really need more feedback to let us know that our information helps...thanks!! – stormy Jan 6 '15 at 19:55
  • Hi Stormy, just an update (not sure if a comment is the best place for this?): the treatment (pruning/systemic insecticide) seems to have helped a lot, there is much less scale and much less sooty mould. However I decided against spraying as it would affect neighbours and it is just far too big. I have been watering and giving it a little food. It is still not healthy though, and I'm considering giving it another dose of systemic in the next month or so. Not sure how long it lasts in the tree's system or how long it remains effective. – Ivan Jan 12 '15 at 14:13

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.