Hi!
I’ve noticed a lot of my 1yr old walnut seedling have gotten black spots on their leaves. I’ve tried searching google, as well as this forum, but didn’t find something matching.
The regular reply using google is anthracnose – however, I do not think my plant leaves looks like all the anthracnose-ridden walnut leaves on the interwebz 
…
Anyone got an idea? Is it a deficiency? A decease? Any bugs who could cause this?
Thanks!
Henrik
Hi Henrik! When was your last frost or temp below 5°C? I remember nights being quite cold at this time of year around Trondheim 25years ago. Low temperatures can damage tender growth on walnuts and any damage will turn black.
Something like this happened to my english walnut seedlings last year. By mid summer most had lost all of their leaves. Most of them survived though…and I suspect some that didn’t would have if I left them alone. No idea what caused it though; could have been transplant shock or something in my case. I started them inside and may not have hardened them off well enough before putting them in the ground.
Hi!
Actually, we’ve had zero frost since mid April – however, last weeks, we’ve had several nights with temps around 2°C-3°C…
If temps below 5°C can lead to this damage, then it’s highly likely that this is the reason for the spots! Thanks btw! 
Henrik, your pictures are typical of anthracnose. With that much leaf damage, I would expect it to spread and cause early leaf drop.
Maybe not 5°C, but 2-3 can when the leaves are very young and thin. I would guess (stress on the guessing) that is your primary cause of damage as it is mostly on the upper leaves rather than in the denser foliage and that opened a gateway for infection. Well established European walnuts can often handle it (anthracnose and its other fungal&bacterial friends) no problem (or with some fruit loss) unless the weather conditions are persistently in favour of the infection.
Since you are in a persistently wet part of the world (though CE feels like pond right now, too) and your plants are young, I’d apply fungicide (even it it weren’t anthracnose yet - to be on the safe side) and fertilise. And fertilise before budding next spring.
Which fungicide should I use? 
Something copper based. If you only have a few plants in pots, use a copper based spray for houseplants if you don’t have a garden fungicide and sprayer. Apply when the weather is wet. Maybe once in 2-3 weeks if you have drizzle on more days than not.
Out of curiosity, are walnuts commonly grown in Trøndelag or are pushing boundaries?
The only walnut I’ve seen in Trøndelag, or the Trondheim area, is juglans ailantifolia at Ringve botanical garden … oh, yeah, now I remember, I also saw two young trees in pots last year - at my local gardener 
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But, no - there are virtually zero walnuts in my region. However, my cold hardiness zone being 7a (although with a growing season 1.5-2 months shorted than central europe 
)…
Pretty much all my plants are rare - or the only specimen - in my region. Not a lot of apricots here, or Burr oaks, pin oaks, american chestnut, mulberry, persian silk tree, pistacia vera, moso bamboo, loquat, liriodendron tulipifera, lebanese cedar, etc… 
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If I need a fungicide, I’ll have to buy an agricultural one I believe, as I’ve got around 25 walnuts in 5L air-pots. But if fungicide is general, will it help with powdery mildew also? Had a horrible break out of powdery mildew on my American chestnut last year - I’ve got about 60 castanea dentata 
…
Thanks,
Henrik
Yes, most of the fungicides will be broad spectrum and list application to apricots, cherries, grapes, potatoes, tomatoes, etc. None that I know list walnuts - it is rarely done on established trees due to their size, so they don’t list it. Only the most common food plants. I don’t know if it will help, but try to space out your pots as much as possible for airflow to give them a chance to dry faster in wind.
Yeah, space… My plant hobby has grown out of space!!! … I need to add 100-150 square meters with fenced in area - I need tall fencing to protect against roe-deer 
… haven’t had time yet, or money, but I’ll maybe have to prioritize it now…
I come from a mountain region which can be rainy for all of our reputed 3 weeks of summer 
, otherwise it used to be somewhat similar to your area, minus the salt. I remember that walnuts from my childhood were about cherry-sized and the trees were affected by cool and wet summers and autumns.
