JRP yellowing needle tips

[Clicio]

It's Spring here in South America and some needles of my cascade red pine are turning yellow on the tips.
New growth (this year's) is blue/green with no yellowing; but old needles have visibly damaged tips.
I have searched online, and at other bonsai forums, but apparently could be from "normal" (old needles) to "killer fungus" (the tree will die any moment).
Any tips ? (no pun intended)
Thanks in advance!
Here below is the Bonhe graph, helpful but not in my case, and below that are examples of my tree at various angles .
Thanks @bonhe !

 

[Wires_Guy_wires]

In overwatered pines I see a lot of yellow tips. I don't see the band pattern of needlecast, but I do see some black round spots that indicate a minor infection.
I think it's a watering issue from the past.

 

[bonhe]

Thanks Clicio,
Your pine absolutely has normal sign of old needles. Don’t worry about it.
Incidentally, Osoyiung contacted me yesterday for possible update of my diagnostic chart which I am going to do it soon. ?
Thụ Thoại

 

[0soyoung]

In overwatered pines I see a lot of yellow tips. I don't see the band pattern of needlecast, but I do see some black round spots that indicate a minor infection.
I think it's a watering issue from the past.

ditto, IMHO. Too much water (i.e., let it dry out more between waterings).

Your pine absolutely has normal sign of old needles.

Also true, but I do think you'll get less of this tip yellowing, @Clicio, with less water (or maybe changing to a 'drier' substrate).

 

[Clicio]

Well, thank you guys!
@bonhe please post it as soon as you update it, it's very useful.
@Wires_Guy_wires , @0soyoung , I was wondering about the watering issue. We're having an unusual wet and cool spring here, and I didn't repot as apparently the soil would stand another season, it is draining OK. But the pot is deep, it's a cascade after all.
Let's see after the rain stops.

 

[bonhe]

Also true, but I do think you'll get less of this tip yellowing, @Clicio, with less water (or maybe changing to a 'drier' substrate).

Some of my pines have this sign and they are in well drained soil and importantly they are all healthy!
Thụ Thoại

 

[bonhe]

Well, thank you guys!
@bonhe please post it as soon as you update it, it's very useful.
.

Yes, I will try my best since I have been preparing for my board next year and others. I have to find the quiet time to sit down and arrange my thought ?
Thụ Thoại

 

[0soyoung]

Some of my pines have this sign and they are in well drained soil and importantly they are all healthy!
Thụ Thoại

Agreed.
I see similar things sometimes on older needles, especially on my JBP landscape specimen.

I also occasionally see yellow tips on newer needles that seems to go away when I reduce my watering frequency. I see this mostly on my JBP and JRP seedlings, but also on a 'thunderhead' in training. I cavalierly decided I 'know' when seeing a post from Jonas making similar 'overwatering' claims (confirmation bias?).

Either way, it has never been severe enough for me to be concerned about.

 

[bonhe]

Agreed.
I see similar things sometimes on older needles, especially on my JBP landscape specimen.

I also occasionally see yellow tips on newer needles that seems to go away when I reduce my watering frequency. I see this mostly on my JBP and JRP seedlings, but also on a 'thunderhead' in training. I cavalierly decided I 'know' when seeing a post from Jonas making similar 'overwatering' claims (confirmation bias?).

Either way, it has never been severe enough for me to be concerned about.

The reason I wrote so is that most of needles have this sign is old needles and not all needles have this sign. By that, the water issue is out of my mind. To diagnose problems, one should have look at all aspects before come into conclusion. This is the way I have been teaching my students in other field for years ?
Thụ Thoại

 

[Wires_Guy_wires]

Herbaceous plants can have burned tips when there's too much salts in the soil. Usually those salts come from nutrients.

People keep telling me it doesn't happen in pines, but pines express the same foliage deformation as herbaceous plants when theres a little too heavy feeding (curling of the foliage). I keep wondering why the 'burned tip' issue can't be just as similar.

 

[0soyoung]

Herbaceous plants can have burned tips when there's too much salts in the soil. Usually those salts come from nutrients.

People keep telling me it doesn't happen in pines, but pines express the same foliage deformation as herbaceous plants when theres a little too heavy feeding (curling of the foliage). I keep wondering why the 'burned tip' issue can't be just as similar.

Logically, I agree with you.

A possible explanation why things don't seem to be this way are leaf structure, veining specifically. For example, is guttation possible with a conifer leaf? I think of burned angiosperm leaf margins as being the low rH version of guttation (also reflecting soil moisture levels).
Another might be the diameter of xylem lumens. Conifers generally have much narrower ones than angiosperms that also have duct structures involved in water transport. I've seen sections of a pine branch apparently living on while the needles to either side of this area are brown and dropping.

 

[River's Edge]

The reason I wrote so is that most of needles have this sign is old needles and not all needles have this sign. By that, the water issue is out of my mind. To diagnose problems, one should have look at all aspects before come into conclusion. This is the way I have been teaching my students in other field for years ?
Thụ Thoại

Over watering usually displays as yellowing from the base of the needle out not the other way around. Older needles often show yellow tips as they age. Simply my observations in concert with other variables. I feel it is important to note all aspects of the situation. Ie: soil composition, water retention, drainage, surface vegetation. Color of Akadama if present.

 

[0soyoung]

Since we're all here, some examples of yellowing pine needles.

First, a pinus bungeana (snake bark pine). I would say that only older needle (expressed in 2017) tips are yellow, but there is some yellowing on new ones that I believe to be seasonal (excess xanthophylls for winter).

Next, a p. densiflora with yellowing on the tips of the long needles expressed in 2017. Then yellow needles (pretty much the full lengths) expressed in the first flush of 2018 and normal dark green needles expressed in the two apical branches of the second flush this year (2018). I have a total of 4 JPB 'mikawa' and 5 p. densi like this example in varying degrees. My conjecture was that the substrate was too wet during the first flush.

Third, a lodgepole pine sapling. Most new needles are strongly yellow, but some are dark green. Since I am now scrutinizing yellowed pine needles, I am unsure of my recollections, but they are that these yellow needles (which were expressed in yellow) will turn green next year (2019) but it may well be that they will just turn brown and fall off. I have a number of these from ArborDay and, hence, have no idea of their provenance. They've behaved this way for a number of seasons now and I really have no good idea why. I've thought about the possibility of these being related to the 'Chief Joseph' cultivar, but CJ turns green in summer, expresses new needles in normal green and turns yellow over the winter (because of an over abundance of xanthophylls) - pretty much opposite what my saplings do. Maybe it is pathogenic?

 

[Wires_Guy_wires]

Logically, I agree with you.

A possible explanation why things don't seem to be this way are leaf structure, veining specifically. For example, is guttation possible with a conifer leaf? I think of burned angiosperm leaf margins as being the low rH version of guttation (also reflecting soil moisture levels).
Another might be the diameter of xylem lumens. Conifers generally have much narrower ones than angiosperms that also have duct structures involved in water transport. I've seen sections of a pine branch apparently living on while the needles to either side of this area are brown and dropping.

I think guttation is possible in conifers, if salt levels are met. Conifers are good with retaining water unless salt levels force them to excrete. There is some anecdotal evidence supporting this http://suffolktimes.timesreview.com...to-blame-for-white-pine-trees-changing-color/. They have stomata and the duct structures all pointing towards the end of the needle would force it to only burn at the very tip and working backwards from there. Like what I think is happening in your second picture. Yellow would be the pre-stage to that.

I'm not entirely sure if all of this is right, but it might put some puzzle pieces in place that don't fit in anywhere else.