It seems recently some of my Alder trees have developed this issue, they are Alnus glutinosa 2-3 years old.
I wonder what could it be, appears to be a pathogen, maybe bacteria or fungus?

Can anyone identify this disease?
If I am not mistaken i have seen this before on other species in photos but I am not sure.

I have to say I am bit upset to see this happening i was looking forward to planting them in the garden this year.

It's Nectria canker: in the last picture (most likely the first lesion to appear) the canker has already taken the diagnostic cateye shape.

The fact so many trees were affected tells me you live in an area of high incidence and that at some point in the past they suffered drought: Nectria always hits the hardest when the weather turns rainy after long spells of drought, especially in the Fall.

To the best of my knowledge there is literally nothing that can be done but help the trees heal by themselves. This means avoiding stresses and especially injuries where further inoculum can happen. Pruning the worst affected branches may be necessary.
If the trees are healthy and no more lesions form, it's very likely they will make a full recovery, albeit the trunks will remain scarred. I have a Beech that fully healed from Nectria canker so if you want to see what awaits you I may post a picture.

Thanks for the reply. Well they had some stress indeed, transportation to me then kept a while just in water with minerals then only planted or potted. They were sent bare roots.
Interesting both the planted and potted one s have this canker.
The growth was something fantastic in just several months they grew a lot and formed very big root systems, especially in the air-pots.

But yeah the area is rather pathogenic so to speak various plants get various issues.
I was hoping this species is more resilient because it likes lots of water.

I started looking around and I have noticed that this same issue is present in some roses and in some hylotelethium, interesting these are quite far from each other and even separated by fences but the issue is present none the less.
Even if I have always washed and constantly disinfected tools and pots.

Maybe the various substrates we have been buying contain the same pathogens and all this washing of hands, gloves or tools becomes ineffective alongside stressful weather.

Even more interesting is how some hylotelethium even if there were side by side the canker ones are actually clean.
I have added some photos.

Roses: 'Paul Noel', 'Felicite Parmentier'.








Hylotelethium (sedum) 'Crystal Pink', and another cultivar.