Is this what fertilizer burn looks like?

[Desert O'Piñon]

I fertilized this honey locust (and all of my trees) about a week ago, and this is the only one that has this occurring. It is only on the very tips of a few branches. I'm not too concerned about overall health, just wondering what might be the cause. I have several seedlings younger than this (honey locust) that have no damage whatsoever. None of my other species have this either. This sapling has been in potting soil for three years from seed (I know, I know, but I didn't know when I planted the seed.), as are the other four 1-year seedlings.

 

[Kievnstavick]

I don't have too much experience on identifying if the damage is fertilizer burn or not. My first thought is that the damage is too concentrated to be fertilizer burn. I'd expect fertilizer burn to show up more systemically as the plant can't hydrate itself effectively.

Are those damaged leaves crispy or are they still hydrated yet curled?

 

[rockm]

Looks like too much sun and possibly underwatering or windy dry air

 

[Desert O'Piñon]

Are those damaged leaves crispy or are they still hydrated yet curled?

They were crispy. I just am not sure what caused it, because I didn't notice it on any other tree, and this one is older than the other honey locusts by at least 2 years. It seemed to only affect the very tips of a few leaves, as in the youngest leaflets on those leaves.
I got a nice big bend low in the trunk, and a potential new leader popped about a week ago, so if I can figure out how to reduce the roots on a legume, this one has potential.

Looks like too much sun and possibly underwatering or windy dry air

This is possible, but why would only this one tree be affected? We've had some hit, windy weather, dry in the 90s, but nithing too extreme for this area. There's still so much I have to learn about how and why one tree does this and its next door neighbor does something completely different.

 

[Kievnstavick]

I'd agree with rockems line of thinking in underwatering. In my experience with the legume leaf, the tree drops some of the bipinatte "leaves"

Taking another look at the plant, it seems that only the outer portions and/or tips of the leaf are the damaged or curled bits.

Now as to help answer your question of why this one burnt and the other ones didn't

Just like you and I, the trees of a same species and different ages have different water needs. It could have been creating a large bend in the trunk caused it to expend a lot of water to help repair the damaged tissue, or because it was damaged ot wasn't efficient in carrying the water to the leaves.

Someone who is sick might drink more water then a comparable healthy person for a more relatable example.

Unless you applied a lot more fertilizer to this plant and not the others, I'd probably lean more towards underwatering.

Knowing the light requirements of your species can also help in identifying correct placement. A plant found naturally in a shady area is more then likely not genetically equip to handle the higher water needs of full sun exposure.

Also, a bit of unsolicited design advice...
The trunk emerging from the soil is quite straight compared to the pretty serious bend you put in it. This leads to a strange visual disconnect in how the tree started and grew with time.

You'll want the tree to have a nice flow to it. So if you have a serious bend like that, the rest of the tree should follow suit. Planting the tree at an angle on the next repotting will help alleviate this somewhat.

Keep at it with those tough bends

 

[Desert O'Piñon]

I'd agree with rockems line of thinking in underwatering. In my experience with the legume leaf, the tree drops some of the bipinatte "leaves".

It's definitely possible it was underwatered, as I've been very careful not to overwater in the heavy soil it's in.

It could have been creating a large bend in the trunk caused it to expend a lot of water to help repair the damaged tissue, or because it was damaged ot wasn't efficient in carrying the water to the leaves.

This could be the case, but it's been a slow bend over about a year using rebar and cord. Every month or two I pulled it down about another inch. This one will probably never be a showpiece, especially with that gnarly nebari (talk about a user name!), but it's a great learning tree. I'm experimenting and practicing some beginner styling techniques. Next year, I'll practice air layering some of the branches I've been shaping, just to see if I can.

Knowing the light requirements of your species can also help in identifying correct placement. A plant found naturally in a shady area is more then likely not genetically equip to handle the higher water needs of full sun exposure.

All the honey locusts around town are in full sun all day. They are also in the ground, and mine is just in a large terra cotta flower pot, so there's obviously a difference. December '26 or February '27 I'll try to repot it in a better substrate.

 

[nuttiest]

When some browning like this happens I snap it off and hold the cutting horizontal and angle cut the end into the trash, to look for any staining of a stem disease.
Also legumes should not need nitrogen.

 

[Shibui]

There are many reasons why one tree dehydrates while others don't.
The first few come to mind because you mention this is older than the others.
Trees that are root bound dehydrate quicker simply because roots have filled many of the spaces in the soil where water was able to sit last year. Every year roots grow and therefore continue to fill those spaces that are so important in the pots. I find it gets progressively harder to water trees each year until a repot replaces some of the roots with fresh soil and fresh spaces for water. This is definitely a thing. I've seen it over and over through 40 years.
Larger trees require more water as they have more leaves. Larger tree in similar pot will obviously dry out much quicker than a smaller tree in similar pot.

Other possible explanations:
Tree at the end of a row may receive less water or more exposure to drying.
Tree in a drier zone in the watering system - usually where sprays don't overlap completely.
Different exposure to wind/sun/etc. It does not take much extra to push a tree into water deficit. We may not even be able to sense the difference, only see the consequences.

 

[Shibui]

Also legumes should not need nitrogen.

Legumes use rhizobium to convert gas N to plant available N but they can also absorb it directly from the soil through the roots. There's no such thing as a free lunch, even in the plant world. The Rhizobia need to be 'paid' to do the conversion so wherever N is available the legumes will take it for free and get a greater benefit from that N.
You will definitely see greater growth on legumes that receive additional fertiliser.

 

[Desert O'Piñon]

There are many reasons why one tree dehydrates while others don't.
The first few come to mind because you mention this is older than the others.
Trees that are root bound dehydrate quicker simply because roots have filled many of the spaces in the soil where water was able to sit last year. Every year roots grow and therefore continue to fill those spaces that are so important in the pots. I find it gets progressively harder to water trees each year until a repot replaces some of the roots with fresh soil and fresh spaces for water. This is definitely a thing. I've seen it over and over through 40 years.

This is the most obvious reason, and I completely overlooked it altogether. The seed was planted in this pot three or four years ago, and has never moved, or any root work done. Also, because I had fertilized a few weeks before this application, it's had an abundance of growth, and more new leaves than ever, so it's transpiring much faster.
Too many roots, lots of new growth, and a keeper who's too careful about ensuring he doesn't overwater. I think we've solved the "mystery." I'll back off and fertilize less frequently in order to slow the overcrowding in the pot.