How to treat Murraya Paniculata with yellow leaves?

[CarolynD]

I have a hedge of Murraya that is on a east facing wall, so gets all the morning sun. The leaves keep turning yellow and falling off and some leaves develop brown patches. I have thought that it is a nutrient issue so I have been putting slow release fertiliser and manure in the soil and spraying fertiliser on the leaves. But this year it is no better. I'm now starting to wonder whether it is a different issue? Does anyone have advice please?

[JacobZ]

Hi @CarolynD,

Considering the applications of slow-release fertiliser, manure and fertiliser being sprayed on the leaves, I doubt nutrients are the issue, if anything an inability to absorb them or an oversupply is the issue.

If the pH balance of the soil is off, it can affect your plant's ability to absorb nutrients. Check out How To Test And Adjust Your Soil Ph for some guidance on this.

I would also refrain from using too many products. I would simply use one balanced slow-release fertiliser such as this Scotts Osmocote All Purpose Controlled Release Fertiliser in early spring and leave it. 

You should also never spray any fertilisers on the leaves as they will have limited affect and they will magnify the UV rays, which can lead to sunburn on your leaves. If you are using any kind of fertiliser, it should be applied to the soil so it can be absorbed by the roots, where it is put to best use.

Allow me to tag our experienced gardeners for their thoughts. @Noelle, @mich1972, @robchin, @mashthyme.

You might also like to check out Planting, Growing And Pruning Murraya Hedges for some further guidance.

Let me know what you think.

Jacob 

[CarolynD]

Hi Jacob,

Thank you so much for your response. These are the fertilisers that I spray onto the leaves of my plants. I was advised by someone at a Bunnings store that the fertilisers are well absorbed through the leaves. I think perhaps my issue could be the soil pH as you have suggested. I will go about testing it as my next job. Thank you! 

[robchin]

HI @CarolynD 

The Murrayas do look quite bushy and otherwise healthy. I am inclined to agree with @JacobZ here - I think you may have a pH issue. If the pH is too high or too low - it affects the plants ability to take up one or more nutrients/minterals/trace elements from the fertiliser even if there is plenty of it available in theory. It is OK to foliar feed but we wouldn't normally think it was necessary for plants grown outdoors like this unless they are really nutrient deprived. These ones are clearly not. Did you do a pH test? What was the outcome? You can adjust the pH of your soil if you need to. The deficiencies won't dissapear overnight but you'll stop the problem getting worse. 

These nutrient and pH charts from Diggers are useful tools: Diggers Nutrient Deficiency Chart - The Diggers Club

There is a secondary problem with the brown lesions on the foliage. They appear quite random from what I can tell from the 1 picture. Certainly  something that needs to be looked at. Could be symptomatic of some insect damage or secondary infection of a fungus caused due to insect damage. I'd want to see some close up photos from above and underside of the foliage to be more definitive. Assuming it's a fungal problem any fungicide application would be useful. 

Good luck. 

[JacobZ]

Hi @CarolynD,

While these products say they are able to be sprayed on the leaves, I would suggest this is halted for the time being until they are back to green and healthy.

Water on the leaves can exacerbate issues like fungus and sunburn, so it would be best to avoid it at this time.

Check the pH balance and see what you find. I'm happy to advise further if needed.

Jacob

[CarolynD]

Hi Jacob,

You were absolutely right! I did a pH test on 3 different areas of soil and they were all about 9 or so. Very alkaline. So, I purchased liquid Sulphur from Bunnings this morning and will follow the instructions to apply all over my garden. Could this be the reason for my lemon tree leaves being constantly yellow too?

Thanks again for all your advice!

[CarolynD]

@robchin 

Hi Rob,

Thank you so much for your input! I did a pH test on three different samples along my Murraya's and yes, they were all around a pH of 9 or so. Very alkaline! So, I've purchased the liquid sulphur this morning and will apply it ASAP. 

As for the brown lesions, here are some close up photos. If it is a fungus, should I apply liquid copper?

[EricL]

Hi @CarolynD 

Thank you for sharing those close-up pictures of your plant. 

The damage visible on the Murraya paniculata (mock orange) leaf in your image appears consistent with leaf spot disease, likely caused by a fungal pathogen such as Phyllosticta or Cercospora species. The symptoms include brown to tan circular lesions with darker borders, which may coalesce over time and cause the leaf to die prematurely.

Suggested course of action:

1. Remove and dispose of all infected leaves (both on the plant and fallen ones on the ground) to minimise fungal spore spread. Apply a fungicide, preferably a broad-spectrum one such as: Copper-based fungicides, Mancozeb (particularly useful if the weather is warm and wet)
    
2. Repeat fungicide applications every 10–14 days, especially during humid weather, as this is when fungi thrive.
    
3. Improve air circulation: If the shrub is planted among others, consider pruning for better airflow and sunlight penetration.
    
4. Water management: Always water at the base, not on the leaves. Wet foliage encourages spore germination and spread.

Let me tag @robchin to make them aware of the photos you posted.

If you need further assistance, please let us know.

Eric

[robchin]

Thanks @EricL 

Can I offer one variation on this: Consider using one of the newer breeds of fungicides that will give you some systemic activity (it will give  you some residual benefit). 

Yates 500ml Anti Rot Fungicide - Bunnings Australia

Again - don't expect miracles in the colder weather but apply it now anyway. 

[CarolynD]

Thank you for your suggestion! I do have that fungicide so I'll get to work with it.

I'm finding black spots all over my garden (recently on my Butterkins and Anthurium). Is this a fairly common thing or is there something going on in my garden?

Thanks again!