Sudden larch death

[WNC Bonsai]

I have been growing some larch for a forest planting. I started in 2018 by purchasing 10 American larch plugs even though I am in zone 7a. I still have all 10 of them. Then in 2019 I decided to add some more for a larger forest. However the American larch were nowhere to be found so I opted to go with 10 Japanese larch. After all, these supposedly are more tolerant of warmer conditions. Well I managed to lose 4 of them in an August heatwave. So in 2020 I went back for another 10 J. larch. By the spring of 2021 I still had all 10 American larch and 16 J. larch. I repotted all but the 6 J. larch from 2019 since they were very large and in large flat pots. All 10 American larches did fine but I got some sunburn on a handful of the J. larches. They limped along for a couple of months and finally 6 died leaving me with 10 American and 10 J. larch. Then over the fathers day weekend one of the big J. larch wilted and died. Initially just the growing tips wilted, followed by their needles going limp. Finally all the needles fell off yesterday leaving only a few small green buds which actually look like they are wilting. I have always attributed this to heat stress but this last one is a puzzler since it was in a group of very vigorous large J. larches. At this point I still have all 10 of the American larch, 5 of the large J. larch from 2019, and 4 of the smaller J. larch from 2020. Does anyone have any experience with J. larch and can comment on this? Is this the sudden larch death I have heard of? Below is a photo showing the most recent loss next to a healthy tree—the two looked identical until last saturday.

 

[butlern]

My larch gets full sun even in extreme heat… but I keep it very well watered. At least 2x each day. And it’s in 100% akadama. Perhaps they got too dry?

 

[0soyoung]

Bad soil (low air filled porosity) and/or over-watering = root death by suffocation. It happens suddenly with Japanese larch in my experience.

I suggest just knocking the plastic pot off the two you've pictured. Dead will have no white root tips; live should have some (on the surface of the root-soil plug) - live guy can simply go right back into the pot.

 

[PA_Penjing]

sounds to me like American larch are potentially more heat tolerant. I've heard the same, that Japanese and European larch were both more heat tolerant than our native larch. But who do I know that has ever run an experiment? no one, well til now sort of. Just because a a piece of information gets repeated over and over doesn't mean it's a fact. Some people still believe that spiders climb down their throats while they sleep, because somewhere along the line some liar said we swallow ten spiders a year in our sleep?! what? Oh and while I'm at it, some folks say the needles don't reduce on larch, I hear that a lot but you can definitely shrink them big time. Myths abound!
Could definitely be a pathogen or problem undiagnosed but I have, first hand, watched many larch die suddenly during the growing season. I have sold mine off because of it. Even the great Jim Doyle has lost all but one of his larch. I was there to see two of them suddenly decline over the last two summers.

 

[rorror]

Could you show us the roots of that tree?

 

[WNC Bonsai]

I will check the roots as soon as I am sure those little green buds fade for sure. The puzzling thing is these guys look so healthy one day and then are gone the next. It sounds like a root thing to me since they suddenly collapse. Phytopthera disease on larch trees is sometimes also referred to in the UK as 'larch tree disease', 'Japanese larch disease' and 'sudden larch death' so I am wondering if that is present here as well? This is the same disease responsible for sudden oak disease in California and my larch plugs came from Oregon.

 

[cbroad]

Could it be from borers?

 

[RKatzin]

My Western larch have been grown in pumice. I just got a new one this spring and changed out the soil to pure pumice and she's doing great. I lost several years ago that I had growing in potting soil. I grew some in turface, and turface/pumice mix and gravitated towards more and more pumice. Now that's what I grow them in and they really flourish. Been a long time since I lost a larch. Even cuttings take right off.

 

[0soyoung]

My Western larch have been grown in pumice. I just got a new one this spring and changed out the soil to pure pumice and she's doing great. I lost several years ago that I had growing in potting soil. I grew some in turface, and turface/pumice mix and gravitated towards more and more pumice. Now that's what I grow them in and they really flourish. Been a long time since I lost a larch. Even cuttings take right off.

I presume your pumice grains are generally larger than those in Turface MVP - right?

 

[RKatzin]

I presume your pumice grains are generally larger than those in Turface MVP - right?

Yes, I sift the pumice into sizes, and use different sizes for different trees and/or different stages of development. The turface is very fine for the most part, most of it passing through a window screen. With the pumice this is the stuff I use for seed starter and cuttings. Most of my trees are in 1/8"-1/4" so yeah that's a big difference.
Now, the turface does well enough, I have a couple of trees still from my days of using just turface still in the same pots, I'm guessing, eight years now. But it's expensive and hard to find and I can get pumice by the yard. No brainer huh.

 

[0soyoung]

Yes, I sift the pumice into sizes, and use different sizes for different trees and/or different stages of development. The turface is very fine for the most part, most of it passing through a window screen. With the pumice this is the stuff I use for seed starter and cuttings. Most of my trees are in 1/8"-1/4" so yeah that's a big difference.
Now, the turface does well enough, I have a couple of trees still from my days of using just turface still in the same pots, I'm guessing, eight years now. But it's expensive and hard to find and I can get pumice by the yard. No brainer huh.

So it seems my suggestion/hypothesis that the problem with Japanese larch is due to root suffocation is also supported by your experience.

Bad soil (low air filled porosity) and/or over-watering = root death by suffocation. It happens suddenly with Japanese larch in my experience.

It gets hot. One instinctively water more frequently. Roots drown. Use a more open substrate (larger grained) and watering more frequently when it gets hot doesn't drown the roots. Instead it just keeps the roots cool and happy.


Regardless. get some pumice for your Japanese larch, @Cofga.

Hardiness and heat zones for larix Kampheri doesn't seem to support ideas that it is the summer heat.

 

[Potawatomi13]

Was repotting done after trees started growing?

 

[Paradox]

I have had one larch for several years.
It's in pumice, lava, akadama. It gets watered every day and is in a spot that gets morning sun and afternoon shade. It seems to thrive under these conditions.

 

[sorce]

It's rather hard to follow the purchase/repotted/death pattern amidst all the text, but it seems like repotting is the culprit.

We definitely don't have enough repotting information to waste time speculating other problems.

Even ones that died before repotting will be subject to when they where last repotted and the condition of the roots then.

I don't like dark plastic pots and I think that may be where your problem lies. The problem being, not being able to figure out why some die and some don't.

I feel like once roots make it to the too hot side of the pot, they die and the tree goes with.

If the core is remaining too wet as well, your sweet spot for root growth will be somewhere in between. The same place where a previously uppotted nursery tree will have all it's good tips at.

So then as long as the roots stay there, it's happy, but when they make it to the edge, they die and kill the tree.

I'd like to see them all with easier to follow information on repotting time, method, etc.

Sorce

 

[WNC Bonsai]

My soil is a mixture of pumice, haydite and pine bark. For these I think I used about 30% pine bark and water goes through them like shit through a goose. So although they are not saturated the pine bark content retains moisture. I pulled the dead one out of the pot and there are plenty of roots but did not see any fresh white tips on the outside of the root ball. Now that it is decidedly dead I will rake them out and see what the inside looks like but there is no sour smell. This roots ball looks and smells just like the ones that are still alive. These trees get full sun until about 1 PM each day and then they are in shade for the heat of the afternoon and evening. I water them each morning about 9am and mist them each afternoon. This still is a puzzler as right now I am running over 50% loss rate with J. larch but 100% success rate with my American larch all treated essentially the same way and in zone 7a.

 

[WNC Bonsai]

Yet another website reference to a larch killer. They don’t say whether it is phytopthera or some other mysterious wilting disease, but I am beginning to think it has found mine.

Pests and diseases: Aphids, caterpillars, scale insects and bark beetles are some of the most common insects that can cause harm to your larch bonsai. The “mysterious wilting disease” is almost always fatal to larch.

 

[0soyoung]

"Wilting diseases" are about a pathogen that either clogs up the xylem directly or causes a damage response that does.

In your autopsy of the sudden-death larches did you find stains in the wood consistent with either of these effects, @Cofga ?

 

[WNC Bonsai]

"Wilting diseases" are about a pathogen that either clogs up the xylem directly or causes a damage response that does.

In your autopsy of the sudden-death larches did you find stains in the wood consistent with either of these effects, @Cofga ?

I am still holding off on that as the cambium is still green. Phytopthera is also known to attack in two ways (1) through the vascular systems, and (2) directly through the foliage. On a previus tree the cambium died a week or so later than the foliage and in soite of the fact that all sources say recovery is unlikely I will keep checking.