Shimpaku - Possible diseases?

[SuperBonSaiyan]

Hello everyone,

I bought a couple of young Shimpaku bonsai starters recently and have been leaving them to grow while I research what potting medium to use.

Upon closer inspection I noticed a few of the tips looked strange on just one plant.

Does anyone know what this is? Is it a disease? Can it spread to my other plants? What treatment should I use? Should I just cut it off? Hopefully I won't have to dispose of the plant...

Otherwise, the tree seems to be growing healthily, with a long shoot extending.

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[Grant Bowie]

Looks healthy with just a few damaged tips. Looks more like accidental mechanical handling damage ie damage during transport or handling of trees. Some masters will slap your hand if you unnecessarily handle the foliage.

Grant

[shibui]

I agree with Grant's assessment.
Overseas there are some diseases that affect shimpaku but I have not seen them here. Just monitor to check that the problem does not get worse on this tree but I don't think you need to isolate this plant.

[SuperBonSaiyan]

Thank you both for your reassurance, it definitely helped put my mind at ease.

[SuperBonSaiyan]

I re-potted the tree today and noticed a number of curl grubs in the soil.

Because of this, I removed most of the soil to make sure they were all gone.

I've read that you're not supposed to bare root conifers because it can overly stress them, but would I be correct in assuming it's more stressful to have curl grubs in the mix?

At any rate, I'm thinking to bare root any nursery plant now, because of possible curl grubs - should I not do this for any reason?

[shibui]

Many things become blown out of proportion in bonsai, including repotting conifers. I've been repotting junipers in the past few weeks and often bare root them.
Young trees like yours are far more resilient so it should not skip a beat after this transplant at this time of year. The older the tree the less resilient they tend to become.

Curl grubs can also be treated with insecticide if you don't want to repot everything. I would be wary of bare rooting deciduous trees that have new leaves open now. Most conifers and natives and deciduous that have not yet opened leaves should still be OK now.
I just monitor soil structure in the pots to spot curl grub infestation. Grubs burrowing in the soil tend to loosen the soil or push up mounds so I can now spot curl grub activity by feeling the soil for soft patches if there's more than just a few.

[SuperBonSaiyan]

Many things become blown out of proportion in bonsai, including repotting conifers. I've been repotting junipers in the past few weeks and often bare root them.
Young trees like yours are far more resilient so it should not skip a beat after this transplant at this time of year. The older the tree the less resilient they tend to become.

Curl grubs can also be treated with insecticide if you don't want to repot everything. I would be wary of bare rooting deciduous trees that have new leaves open now. Most conifers and natives and deciduous that have not yet opened leaves should still be OK now.
I just monitor soil structure in the pots to spot curl grub infestation. Grubs burrowing in the soil tend to loosen the soil or push up mounds so I can now spot curl grub activity by feeling the soil for soft patches if there's more than just a few.

That's great to know. I'd rather get rid of poor soil now (especially right under the tree) while the tree is still able to handle it. Gives it a good head start so I (hopefully) won't need to bare root in the future. Even if I do, it'll be easier to remove larger grain substrate than general potting mix.

[SuperBonSaiyan]

One of my shimpaku is getting bronze foliage...

Here are some pictures. I'm concerned it may be in trouble but I don't know why.




It has been in the same potting mix as the others, in the same position, watered the same, fertilized the same...

In one of the pictures is a side by side with a perfectly healthy plant.

Why would one tree get stressed and the other few be fine?

Any idea what is causing this and how I can keep the tree healthy?

[SuperBonSaiyan]

Had a closer look at this tree and noticed a few specks of brown / black on the foliage.

Not sure what it was, but it was fairly stuck to the foliage, and I had to scrape it off with a fingernail. When squishing this brown / black speck, it just mushed apart - not a bug...

I inspected the other trees around this one and saw a few with the same speck (a ball around 0.5mm wide). I removed all the other specks. Found none in the trees further away.

Couldn't take a picture as it was too small to focus on with my phone camera, but imagine the size of this full stop.

No idea what it is - some type of fungus? mold? Hope the tree recovers anyway.

[treeman]

I'm concerned about the plant on the right. It appears to have been infected with one of the juniper diseases.
Possibly Phomopsis Tip Blight:
''This disease is caused by the fungus Phomopsis juniperovora and begins by infecting the tips of branches smaller than the diameter of a pencil.
The new, immature growth becomes infected while the darker green, mature foliage remains resistant to infection. Infected twigs first become pale, then turn reddish-brown and finally become brown after death. Scraping away the bark will reveal a sharp line between discolored, dead wood and healthy wood. Watch for disease development during the spring or summer flush of new growth when warm, wet conditions are present.''

Also possible.... Cercospora Twig Blight:
''This disease is caused by the fungus Cercospora sequoiae var. juniperi. It begins by infecting the oldest needles that are located on the lower branches, inside of the plant. As disease development progresses, the needle browning spreads upward and outward. Branch tips usually remain healthy and green. Needles of spur branches turn brown and die usually in the late summer, leaving a plant with an inner crown devoid of foliage. This disease is sometimes confused with mite damage''.

In my experience, once infected they can continue to survive for some time but do not fully recover and even if you prune out the damaged parts and spray they inevitably show diseased branches again.
Whenever I find this in any of my plants now, I destroy them regardless of their development. I also disinfect my cutting instruments with a flame before and after I cut junipers. Dipping in methelated spirits is probably ok too. The problem is ''controlled'' to some extent but continues to appear in a very small percentage of plants. A regular preventative spraying with a copper based fungicide or Mancozeb should probably be standard practice. It is probably also a good practice to spray for insects as they may be vectors. This (these?) diseases were not seen here in junipers 20 or 30 years ago but it seems they are here to stay and should be ruthlessly dealt with as soon as they are observed.
I have seen this in itowigawa, and the ''blue'' shimpaku but more infrequently on Kishu. Plants such as J. X Media ''Mint Julep'' and J. sabina seem to be very resistant or completely immune.
Everyone who has such plants, please remove them from your collections and spray and observe them, do not propagate from them and if the problem persists - burn them.

[SuperBonSaiyan]

Thank you for the detailed response. I'm worried about the other plants I have near this one now - I've since isolated it, but who knows whether the others are infected. Guess only time will tell.

A regular preventative spraying with a copper based fungicide or Mancozeb should probably be standard practice. It is probably also a good practice to spray for insects as they may be vectors.

I'll buy some copper based fungicide shortly and spray the lot with it. Would you recommend pyrethrum for insects? I've sprayed that on my maples before which resulted in leaf burn, but if conifers are more hardy I'll give it a go.

Thankfully I haven't noticed any issues on the Itoigawa - that's kept separate from these younger Kishu's. Again the question - would you recommend I spray copper + pyrethrum on the Itoigawa as a preventative?

Lastly, when doing a closer inspection yesterday I noticed a number of black aphid bugs around the stem of one of my Kishu's... so it may well be that they're the vector (hence why I'm considering the spray with pyrethrum).

Edit: One more thing to ask - when using fungicide or insecticide - is it better to spray more often at a lower concentration than recommended (over a few days), or to use the recommended concentration?

I figure the recommended is for plants growing in the ground, not in a constrained environment like we practise in bonsai.

[treeman]

. Again the question - would you recommend I spray copper + pyrethrum on the Itoigawa as a preventative?

If you are worried about infection, I would recommend regular spraying. It certainly can't hurt. Always check possible chemical damage by spraying a small unwanted section and observe that for a couple of days before going the whole hog.

Lastly, when doing a closer inspection yesterday I noticed a number of black aphid bugs around the stem of one of my Kishu's... so it may well be that they're the vector (hence why I'm considering the spray with pyrethrum).

Edit: One more thing to ask - when using fungicide or insecticide - is it better to spray more often at a lower concentration than recommended (over a few days), or to use the recommended concentration

No use recommended concentrations but test first. Definitely get rid of aphids. Maveric insecticide was used for aphids by a commercial fern grower I knew and he reported no damage from that so it must be quite safe.

[shibui]

ALWAYS use pesticide/fungicide/herbicide at recommended concentrations.
Diluted insecticides/herbicides,fungicides can allow some resistant pests to survive and breed. That's where chemical resistance comes from.
Stronger than recommended use may damage the plants.

[GavinG]

Thanks for your advice, Shibui, which is always generous, useful and crisp. Once you get to 30,000 or so "thanks" we may propose you for a knighthood - "Sir Shibui of Yackandandah" - I can hear it now, bellowed out over the halls of Buck House.

Gavin

[SuperBonSaiyan]

I'm a bit paranoid about my Itoigawa now. It's kept separate from the problem Kishus, but I noticed the growing tips were a little brown. Not sure if this is normal or not - so I took a few pictures to show.




Should I be concerned about this? Would rather treat early if needed, but will leave it alone if this is normal.

Most of the growing tips are fine, except for the ones where my fingers are holding them up in the pictures.

Finally - is any tree susceptible to disease? Or is it only "weak" trees? E.g.: Does keeping up with fertiliser, water, air flow to the tree help it naturally fight off disease?

Thanks.