Unhealthy Western Larch Unidentified Pest

[lillarch]

This Western Larch has had a rough growing season. As icing on the cake I noticed one of the branch tips has a large number of what look like eggs (see photos below).

I have been trying to figure out why suddenly in mid June my larch trees started dropping needles. It was odd because the Seattle area didn’t see many days over 75 deg until late June. Conversely, we experienced an unseasonably warm late January-early February with many daily temperatures exceeding the historical average by 5-10 deg F. See photo below of larch buds moving from January 22nd! I unfortunately decided it was a good time to repot. Soon after in late February we experienced freezing temperatures again. It is my theory that this period of unseasonable warmth and repotting followed by freezing temperatures shocked the Larch trees and caused the problems I saw later in the spring and early summer and the pests I am seeing now.

1/22/22 Larch buds moving early after warm January


2/4/22 Mistake to repot. Fooled by warm temperatures in mid winter.



6/24/22 Weak new growth followed by needle drop. Apex lost less but still saw browning and dropping



9/16/22 unhealthy foliage with yellow tips and no vigorous growth



9/19/22 unknown pest


9/19/22 unknown pest eggs

 

[andrewiles]

How much root mass did you remove when you repotted? I suspect you're correct and the early repot stressed the tree this summer. It looks like you have good buds set for next year so you should be ok come spring.

We also had a very warm summer with a record number of 90+ degree days. So stressed tree plus shallow hot pot also may have tripped it up. I know this wouldn't explain the June behavior but it might explain why it didn't bounce back with a second good flush in July and August.

No idea what the eggs are but seems they would be unrelated to the sluggish growth this year. I'd clean off those needles and focus on the other issue.

Also wouldn't hurt to protect the pot from deep freezes this winter, if we have any.

 

[lillarch]

How much root mass did you remove when you repotted? I suspect you're correct and the early repot stressed the tree this summer. It looks like you have good buds set for next year so you should be ok come spring.

We also had a very warm summer with a record number of 90+ degree days. So stressed tree plus shallow hot pot also may have tripped it up. I know this wouldn't explain the June behavior but it might explain why it didn't bounce back with a second good flush in July and August.

No idea what the eggs are but seems they would be unrelated to the sluggish growth this year. I'd clean off those needles and focus on the other issue.

Also wouldn't hurt to protect the pot from deep freezes this winter, if we have any.

It was growing in a 5 gal pot that had its rim cut to be about 8” deep. Took about 4-6” off the bottom of the rootball when it was reported into the pot you see in the photos above.

 

[Leo in N E Illinois]

My experience with larch is limited to eastern larch, Larix laricina. Here, if the winter is not cold enough, the eastern larch gets all screwed up and dies. Eastern larch is difficult to grow in climate zones 7 and warmer. It really does best zone 6 and colder.

You are in zone 8. Seeing any green at all on a larch in January suggests it was being wintered too warm. I do not know specifically the winter requirements of western larch, but most larches fail if winters are not cold enough. Consider if that is a possible cause of your trouble.

 

[0soyoung]

Many different varieties of larch are common landscape trees in my environs; both Japanese (kaempferi) and European (decidua) and others that appear to be distinctly different (but unknown to me).

I suspect the roots have been drowning. Watered too frequently and/or a substrate with insufficient air filled porosity. Under 'watered too frequently' one should note that this becomes particularly problematic with shallow pots that have "ample room (width) for growth".

 

[lillarch]

Many different varieties of larch are common landscape trees in my environs; both Japanese (kaempferi) and European (decidua) and others that appear to be distinctly different (but unknown to me).

I suspect the roots have been drowning. Watered too frequently and/or a substrate with insufficient air filled porosity. Under 'watered too frequently' one should note that this becomes particularly problematic with shallow pots that have "ample room (width) for growth".

Thanks for the information. Could you please elaborate on shallow pots being more problematic with over watering? I also have a suspicion that Western Larch has different water needs than other species of Larch that others find in bogs. I have heard for years that Larches like a wet environment and to keep the soil wet. The environment in which I found this and my other Western Larches is quite dry in the summer as it is east of the Cascades. When I am there in the summer the ground is not even close to bog-like where these trees grow.

 

[Leo in N E Illinois]

Many different varieties of larch are common landscape trees in my environs; both Japanese (kaempferi) and European (decidua) and others that appear to be distinctly different (but unknown to me).

I suspect the roots have been drowning. Watered too frequently and/or a substrate with insufficient air filled porosity. Under 'watered too frequently' one should note that this becomes particularly problematic with shallow pots that have "ample room (width) for growth".

Yeah, I probably should not talk about what grows or doesn't grow in your neck of the woods, I really don't know much about the Pacific Northwest. Folks, follow @0soyoung 's lead, I don't really know that much about the Pacific Northwest.

 

[Potawatomi13]

From 1959-1989 had one Western Larch in flower pot with garden dirt substrate amazingly did fine until miserable worthless neighbor did not water when vacation time came. Never had any Winter protection.

 

[0soyoung]

Thanks for the information. Could you please elaborate on shallow pots being more problematic with over watering? I also have a suspicion that Western Larch has different water needs than other species of Larch that others find in bogs. I have heard for years that Larches like a wet environment and to keep the soil wet. The environment in which I found this and my other Western Larches is quite dry in the summer as it is east of the Cascades. When I am there in the summer the ground is not even close to bog-like where these trees grow.

With every medium there is a level that is effectively saturated with water, depending upon the particle size (and to a lesser degree, shape). With tall/deep nursery containers, the layer of saturated soil is typically far below the plant's roots. In shallow pots, the tree's roots are in the saturation zone which means they will not get oxygen until the substrate/soil dries so that enough air can fill the pores to sustain the roots.

Species that are said to 'like' water, such as maples and spruce, have roots that rapidly adsorb water. In my view, this is why maples can be grown in trays that are only an in humor two deep. Conversely, one has great difficulty putting pines in such shallow pots - their roots do not adsorb water rapidly. Further, the wider the pot compared to the root spread, the greater is the volume of water that must be removed before the roots to get air. One can actually drown a root pruned maple returned to the same pot by watering as was previously done (I've done it --> one must reduce the frequency of watering after repotting, depending on the extent of root reduction).

I think this also explains why there is a 'rule' to cram pine bonsai into the smallest possible pot and why that pot is usually several inches deep. Furthermore, one tends to use deep pots and a much larger grain size substrate when growing out pines than most other species (or, this is my experience).


The condition of your larch is similar to what I have experience with drowning pine seedlings. Likewise, cutting off half of the root plug and plopping it into a bonsai pot is a familiar experience, though not specifically with larch. Maybe change the substrate to quarter-inch (-ish) pumice or a Cinderella sized pot if you are done with development. As you said, things suggest making 'drier' root conditions is a good idea.

 

[lillarch]

Update: Some of the new spring foliage has started to yellow already. This coincided with the first stretch of sunnier weather. Any thoughts about what is causing this and what to do?

 

[andrewiles]

I've seen this as well, and have some collected larches that also have some yellow needles right now. And yeah, it coincided with our warm stretch. I also have western larches in full sun that have no yellow needles, so they can clearly take that 80 degree weather and our zone 8 warm winters. In their native habitat they certainly get above 80 in mid summer, though root temps are considerably lower all summer.

I don't know the underlying cause. I'm also still learning the species. My best guess is that they are having difficulty growing roots aggressively in our climate and can be water stressed quickly if it warms up. I'd wager it's root temps rather than foliage temps, but these are all guesses. If I keep mine out of afternoon sun, or have them under mist, they don't tend to show yellow needles. Both of these approaches reduce transpiration but also, perhaps more importantly, pot temperature. If they go through a full season in this healthy state they are less likely to have trouble the next year, even with more sun and no mist.

This would seem to match your case as well, since your tree was stressed with root reduction last year and was weak. And it's in a small pot that can heat up quickly.

My 2 cents is that you should keep it in morning sun and mist periodically this year, trying to keep the roots cool.

Hopefully others have more definitive data here. I'd really like to understand this probablem as well.

 

[lillarch]

Update 11/1/23: Tree was healthier this season and kept more of its foliage through the growing season. It has more foliage than in the photos from last fall. My theory is that the tree would be healthier if it was in a pumice, pine bark, lava 1:1:1 mix rather than the organic native soil it is in. Its watering cycle is 3x as long as other larches in more free draining soil. Goals for next two growing seasons are to get it into more free draining soil and a deeper pot to achieve better drainage.