How to save dying english boxes?

Hi everyone,

I’m really worried about my English box plants and could use some advice. I have three of them, and over the last few months they’ve been getting worse. It started with one plant, then another began showing the same symptoms, and now they’re all struggling.

I’ve been trying to fix this for at least 4 months with no success. I’ve been pruning them weekly, tried using horticultural oil, and last week I started applying Bug Killa granular garden insecticide — but so far, no improvements.

I’m not even 100% sure it’s scale. I’m attaching some pictures so you can help identify the problem. Here’s what I’ve noticed:

Some branches have large, black, hardened bumps stuck to the stems (they look like domed shells, rough to the touch).
Some leaves have tiny black specks scattered across the surface.
New foliage is turning black, and in some cases part of the leaf also turns brown and dies off.

I love my English boxes and really don’t want to lose them. Can anyone help me figure out what’s going on and what I can do to save them?

Thanks so much in advance.I'm not sure what are these black spots, they don't look like scales to me.Looks like scaleLooks like scaleSome new foliage is turning black

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Comments

MitchellMc

Welcome to the Bunnings Workshop community @raonic. It's wonderful to have you join us, and many thanks for your question about saving your plants.

From your photos, there are definitely some hard black scale present, but not in the kind of numbers that would usually be the sole cause of the amount of dieback we’re seeing. Typically, if scale were the main culprit, you’d expect to see many more insects covering the leaves and stems.

It’s also important to remember that once leaves and branches have died back, those areas won’t regrow for some time — often not until the following growing season. So, the horticultural oil and other methods you’ve used may well have already killed off the majority of the scale, leaving only the minimal numbers we can still see.

A useful question to ask is whether the decline has continued since you began treatments, or if most of the damage was already done beforehand. If things have been getting progressively worse despite spraying, then it’s worth considering other possible causes.

One place to start is by checking your soil moisture levels and reviewing your watering regime. Both overwatering and prolonged dryness can stress box plants and make them more susceptible to pests and disease. If you can share more about your watering schedule and the soil condition, it might help narrow down the problem.

Please let me know if you have any questions.

Mitchell

raonic

https://www.workshop.bunnings.com.au/discussion/comment/55783#Comment_55783

Hi Mitchell,

Thanks for your reply.

To answer your question, unfortunately the decline has been continuing even after I started treatments. The first plant began showing symptoms around four months ago, and since then the damage has kept progressing — first to the second plant, and now the third. Even after using horticultural oil a few months back and starting Bug Killa last week, I’m still seeing more blackened leaves and dieback on new growth.

Regarding watering — I usually water them once or twice a week, depending on the weather. I use a soil moisture meter to try to keep the soil moist but not soggy. The soil feels like it drains fairly well.

If the scale isn’t the main issue, what other pests or diseases could cause this kind of blackening and browning on new foliage?

Thank you.

MitchellMc

https://www.workshop.bunnings.com.au/discussion/comment/90167#Comment_90167

Hi @raonic,

Given that the blackening is in the leaf tissue itself and not a surface coating like sooty mould, and considering the flecked or speckled pattern on the leaves, this could point towards a fungal leaf spot disease or possibly a viral infection. In box plants, fungal issues such as box blight or Volutella blight can cause leaves to develop small dark spots or speckles that expand, leading to the whole leaf blackening and dying.

If it’s fungal, the best steps would be to remove and dispose of all affected foliage (bag it rather than composting), prune to improve airflow, and treat with a broad-spectrum fungicide safe for ornamental shrubs. Cleaning your tools between cuts with methylated spirits or a disinfectant will help prevent spreading the problem.

Viral diseases can produce mottling, speckling, or unusual patterns in the leaves, and unfortunately, there’s no direct cure — infected plants are usually removed to stop the spread. That said, fungal problems are far more common in English box than viral ones, so it’s worth trialling a fungal treatment first to see if you can halt the progression.

Mitchell

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