Needle cast on Pinus sylvestris

Horticulture
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Grab something to drink or eat, this will probably be a long one, but I want to give all info possible.

I collected a pine in spring of 2019, with a good root ball and planted it in pure pumice, didn’t touch the native soil. It grew ok last year and had a lot of buds this spring, even some buck buds. All seemed great, it had clearly survived the collection and seemed to be headed for a great growing season 2020.

In mid May I noticed the first 2nd year needles started to drop. I wasn’t worried as it had dropped needles quite early the year before as well. And only the weakest two year old needles were shedded. Some had black/dark spots but I thought it was some leftover damage from a scale infestation I had last year. In the past weeks more and more old needles have been falling but the candles have been extending nicely so I thought maybe the tree was balancing needle mass to give room for the new growth. We had an abnormally wet winter so I figured maybe some roots had died and the tree couldn’t support all foliage so it was shedding the oldest.
But the last few days I’ve started seeing last years needles also dropping and that’s when I noticed a distinct yellow/red/brown banding around the dark spots, so now I strongly suspect it’s needle cast.

I directly treated with a home remedy spray of apple vinaigrette, soap and water. I’ll get fungicide on Monday and start treatment. But due to my slow response the fungus has spread quite widely and I’m afraid I might lose almost all foliage apart from this years new growth.

So my questions are:

  1. Should I try to remove all infected needles, even the ones still firmly attached to the branches (to reduce the amount of spores) or do I let the tree discard the needles and pick them off when they almost fall on their own (to let the tree retrieve everything it can from the needle)?
  2. If I’m left with only this years needles on the tree, how likely is it for the tree to survive?
  3. Apart from being careful not to overwater and treat with fungicide, is there anything else I can do to help the tree recover?
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In his book BONSAI HERESY Michael recommends putting a tree suffering from overwatering into a Anderson flat or pond basket with two inches of pumice in the bottom and on all four sides. Do not disturb the roots but look to see if they appear black and rotted. I have a Ponderosa pine and a Douglas fir in flats now, and have seen positive results. I am learning to observe the trees before watering!
:thinking:

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As I said, I’m very confident it’s needle cast, not overwatering. The needles have the characteristic banding caused by needle cast and don’t have a uniform brown tip.

The tree is already in a very flat grow box with a lot of aeration in the bottom, with coarse pumice in the bottom and on the sides. So I don’t think moving it into another pot is worth the risk to accidentally break up the root ball during the transplant.

But I’ll be sure to be very observant with my watering, as I have been thus far. I only water the field soil starts to feel dry.

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So, the needle cast that you are seeing is last year’s infection. The spores infect the needle during the time when the first push from the candle but before they harden off. This is the time to spray fungicide to prevent an infection of this year’s needles. I apply every two weeks alternating between daconil and copper until the cuticle forms on the new needles.

I have observed that pines with poorer root health tend to be more susceptible to infection. Strong pines never really seem to get hit. I also only spray trees that have an outbreak to break the cycle then I look to improve the root system dynamics.

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