How to treat Tahitian Lime new leaves turning black?

[Nabila]

Hi,

I have a Tahitian lime, 1 year old. I use lime fertilizer fortnightly and the citrus spray for it whenever needed. It gets full sunlight. Recently there are a lot of new leaves in the plant. But today I just spotted the new leaves are turning crispy black. First I thought it might be soothy mould. But it's on edges on many new leaves and they are kind of crispy. I checked the water level and seems fine. Not sure what to do. Please advise.

 

 

  

[MitchellMc]

Hi @Nabila,

Could you please show us what fertiliser you're using fortnightly? Not many citrus fertilisers require such a regular reapplication interval. I want to ensure this blackening of the leaves isn't due to overfertilisation.

As you've likely found when searching for black leaves on citrus, the results are flooded with sooty mould, as it's quite common. I don't believe that is the issue here.

Let me call on one of our horticultural experts, @Noelle, to see if she has some thoughts.

On a side note, it would be great if you could supply some images of the base of the trunk around the graft line from all sides. You have some quite lanky leading shoots, which appear to come from down low. This is unrelated to the blackening leaves, but you might have a case of suckers from the grafted rootstock that need to be removed.

Please let me know if you have any questions.

Mitchell

[Nabila]

Hi Mitchell,

Thank you for your prompt response and help.

I am sending here the pictures. The plant had 3 root suckers that I cut already in January this year. But I could not completely remove the shoots. I tried but realised it is not possible to cut it from base with my pruners. I need something like knife shape maybe. I don't know. I fertilised the lime plant two days ago. Thank you again for your help.

  

 

    

[MitchellMc]

Hi @Nabila,

When applied as directed, Scotts Osmocote 500g Citrus and Fruit Controlled Release Fertiliser lasts up to six months. So, if you've been applying it every two weeks, this could be a reason for the leaves turning black. I would suggest you stop fertilising.

It's great to see you've nipped off those suckers. I'm not entirely convinced those three lower shoots right on the graft line are not suckers too. Do any of them end up being this lanky growth I've circled below?

Mitchell

[Nabila]

Hi Mitchell,

So are my leaves going to die? Pretty much all of the new leaves are turned black. Can they survive?

About the root suckers, I am not 100% sure. The lanky growth have a small flower bud and I thought it's from the lime plant. The lanky growths did not come from the lower trunks. Would you please take a look at other photos and let me know if all the trunks are above the graft line please? 

Is my lime plant going to die now? It just got its first flower in 2 years.

Thanks for your help.

 

 

 

  

    

[MitchellMc]

Those shoots appear to be coming from above the graft line @Nabila, so you'd presume they were normal growth from the plant and not suckers.

I haven't been able to find information that would point to a cause for the blackening of the leaves. It also does not look similar to what I'd expect from fertiliser burn; I believe the leaves would brown and drop. This appears to be a specific affliction and my hopes are that @Noelle or @mich1972 might be able to provide some insight.

Mitchell

[Nabila]

Thanks Mitchell 

[Noelle]

Hi @Nabila 

The black leaf margins on your Tahitian lime may be the result of two or three issues.

Mitchel has already touched on over-application of the Osmocote Citrus fertiliser - while the blackening isn't typical of fertiliser burn (as in too much nitrogen burning leaves) it can be caused by an over-supply of minor and trace elements including iron.

It can also occur when there is an abundance of soft new growth (stimulated by over-feeding) during colder weather - cold wind can cause damage like this, as can frost.

The very long spindly growths need to be cut back quite hard and the weaker of the side shoots coming from just above the graft union (where the bark on the main stem changes colour) should be cut out. Because the tree has had too much fertiliser available, especially nitrogen, it has produced abundant stem growth at the expense of flowers and fruits.

I would be inclined to cut it back, repot it into fresh citrus potting mix and not add any fertiliser at all until late Spring - fresh mix will have fertiliser in it to keep the plant healthy until then.

[MitchellMc]

Great advice, @Noelle; I trust @Nabila appreciates your expert input.

Mitchell

[Nabila]

Thank you so much Noelle. I appreciate your help. Sorry for late response. I did not realise I have a notification. Thanks again. I will follow accordingly and update you all.