Is this Box blight? How do I deal with it?

[HarryHsieh]

Hi, 

These plants have been at the property when we bought it so I don't know exactly what it is. By looking up it might be a Box bush? There are 3 bunches of them in different big pots. They have been slowly dying of different pace but I don't know what to do with it (photo taken after cutting some leaves and branches off). Is this box blight or something else? I can't find caterpillars on them. What can I do with them?

Thank you!

[EricL]

Hello @HarryHsieh 

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

Would it be possible for you to post a close-up picture of the leaves of the first plant. It looks like a fungal infection judging by the uniform appearance of the leaves. Box blight if I recall correctly look like burn marks on the edges of the leaves and you get black marks on the branches and twigs as well.

When you touch the surface of the leaves does it have a powdery residue on its surface? Does it have a distinct mouldy smell? Do you see any insects crawling under the leaves? Any extra information you can share with us about your plants will allow us to give you a better diagnosis.  

If you have any other questions we can help with, please let us know.

Eric

[HarryHsieh]

Hi Eric,

Thank you and thank you for getting back to me. I have taken a couple of leaves to take photos of. I can't find any insects crawling, but yes the leaves do have a powdery touch. 
Some leaves I previously cut off had very tiny black spots on them that when I touched would become black powder on my fingers. 

I hope these help you diagnose better!

Appreciate it,

Harry

[Jason]

Thanks for the extra detail @HarryHsieh.

Let me tag expert @Noelle to see if she can share her thoughts on your plants.

Jason

[Noelle]

Hi @HarryHsieh 

In my humble opinion, your plant looks to be infected with a mildew of some sort, especially as the powder you have found present is blackish in color. Mildews usually occur on the undersides of leaves but may show through on the upper surface as discolorations, as per your close-up photos of the leaves.

Box Blight does not involve powdery fungal deposits. It is prevalent in the UK and is now in Australia and NZ. Often the first sign is leaves developing a burnt appearance. Your plants don't look burnt but definitely do look like they're infected with a fungus.

Start by treating affected plants with a general copper-based garden fungicide making sure to thoroughly wet the foliage especially the undersides of the leaves. If you are not all that keen on the plants, then it may be best to bin them, wash the pots thoroughly and start afresh with something you do like.

[HarryHsieh]

Hi Noelle,

Many thanks for your opinion. I will have a look in the store for the fungicide next time!

Harry