Author Topic: Black spot on my Chinese elm  (Read 9271 times)

tanlu

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Black spot on my Chinese elm
« on: June 28, 2011, 11:11 AM »
I need help.

My Chinese elm (mall-sai) has black spot. I used a fungicide, but it keeps coming back. I actually repotted it a month ago because I thought it was a root problem since the tree was still in it's nursery pot with potting soil. The tree is now in pure turface, the roots looked fine, but there is an unsightly bulge at the bottom that I cut off during the process. Now the tree is significantly weakened, and the black spot isn't going away. I'm thinking I should just buy a stronger fungicide since the one I have is earthtone, which I hear is too gentle.

What should I do at this point?
 

plantmanky

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Re: Black spot on my Chinese elm
« Reply #1 on: June 28, 2011, 11:44 AM »
There is a fungicide to treat black spot on roses available at most of the box stores (lowe's, etc....)  You'll need to spray with it every 10 days or so and after each rain for the next month or so to get it under control.  This fall as you put your tree away spray it with a dormant spray of lime sulphur and horticultural oil at least 3 times during the winter months and then again as you see the buds color up next spring.  That should pretty much rid you of the problem.  Also, you need to keep all of the infected foliage off of the tree and off of the soil around the tree.  Elms are tough buggers and can come through a bout of black spot without much trouble at all.

hope that helps,
Randy
 

yamins

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Re: Black spot on my Chinese elm
« Reply #2 on: June 28, 2011, 03:45 PM »
Tanlu -- ALL of my elms got black spot last year, a few times.   The infections spread when weather was cool and rainy, which we have had a lot of lately.   

The solution that I arrived at eventually was to  remove ALL the diseased leaves (even those with just one spot) as soon as they were seen -- which meant removing hundreds of leaves from each tree the first time and then 10-20 leaves each day as the arose, for about a week.    This led to the total defoliation of two of the trees and near total defoliation of the rest.   At the same time,  I sprayed very thoroughly with daconil, a fungicide that is widely available (e.g. home depot, lowe's).     

Elms are very hard, so the defoliation wasn't much of a problem -- and they popped out a completely new set of smaller leaves within a few weeks.    We continued to have rain, but the daconil may have prevented the spread of the fungus to these new leaves (it won't "cure" already-spotty leaves.)

I now repeat the daconil before putting the trees away for winter, and then again when the trees are budding out, and continue to do so once every six weeks or so -- as we've been having a very cool, wet spring and summer.     So far this year, I've had almost no spot disease. 


 

yamins

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Re: Black spot on my Chinese elm
« Reply #3 on: June 28, 2011, 03:51 PM »
Also -- plantmanky's advice about making sure the infected leaves are not left around the plant seems is, I think, very important.

The first time I had the disease last year, I left some infected leaves lying around.  The second time I did the defoliation, I first put the tree on a large plastic bag, did the work welll away from the garden, and then threw away all the infected leaves in the home garbage.    Also, I disinfected the shears after the process (something I now do after every working on each and every tree).   

Following some kind of isolation protocol seems useful to prevent disease spread ...
 

tanlu

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Re: Black spot on my Chinese elm
« Reply #4 on: June 29, 2011, 12:26 AM »
Thanks everyone for your thoughtful comments. It's been very helpful, and I'll be extra careful in disposing the diseased leaves. I'm also going to keep the elm quarantined in a completely different part of the yard. It's been within a few yards or so of my Korean hornbeams, but hopefully that haven't been infected yet.

T

 

plantmanky

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Re: Black spot on my Chinese elm
« Reply #5 on: June 29, 2011, 08:16 AM »
I'll be extra careful in disposing the diseased leaves. I'm also going to keep the elm quarantined in a completely different part of the yard. It's been within a few yards or so of my Korean hornbeams, but hopefully that haven't been infected yet.

T

T,

Hornbeams are not likely to get blackspot so I wouldn't worry about them.  Black spot is most prevalent on members of the Elm family which would include Zelkova if you have them.  Roses are also affected greatly by black spot when it's around.  Black spot is a fungal disease and is transmitted from plant to plant by spores that float in the air and lodge onto the bark  and twigs of trees.  The best remidy is to ensure proper winter care by applying dormant spray and keeping infected leaves and branches away fromyour growing area.

R
 

Tim Gardner

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Re: Black spot on my Chinese elm
« Reply #6 on: June 29, 2011, 09:24 AM »
Do you put your elm in full sun?
 

tanlu

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Re: Black spot on my Chinese elm
« Reply #7 on: June 30, 2011, 01:13 PM »
Thanks again Randy. I sprayed it yesterday with a fungicide that looks like milk. My friend uses it for tomatoes. I used it on my Ishizuchi five needle pines which coincidentally also started to have some black fungus on the old needles, which have been plucked. No more signs of infection as of yet. Do you think that fungus on my JWPs is related to black spot found on my Chinese elm??

I'll keep my elm were it originally was then because I don't have any other trees that would get infected by it. It receives 6 hrs of full sun from early morning to early afternoon.
 

yamins

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Re: Black spot on my Chinese elm
« Reply #8 on: June 30, 2011, 02:03 PM »
From my understanding of how plant diseases usually work, I think it's very very unlikely that your elm will infect other non-Ulmus trees, or that the black spot fungus is related to whatever problem you're having with your white pine.   Even the black spot on roses is caused by a completely different disease agent (though they look similar and probably co-occur because they're both favored by cool, rainy weather).

I think it is much more important that your elm get absolutely as much sun as possible, and that the issue of spreading the infection to other (non-elm) trees is secondary ... if there's a conflict, definitely put the tree where it gets more sun, as that will be key in stopping re-infection and in prompting new growth. 
 

plantmanky

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Re: Black spot on my Chinese elm
« Reply #9 on: June 30, 2011, 03:17 PM »
Even the black spot on roses is caused by a completely different disease agent (though they look similar and probably co-occur because they're both favored by cool, rainy weather).

I think it is much more important that your elm get absolutely as much sun as possible, and that the issue of spreading the infection to other (non-elm) trees is secondary ... if there's a conflict, definitely put the tree where it gets more sun, as that will be key in stopping re-infection and in prompting new growth. 

Black spot on Elms and Roses are the same identical fungus  They have different stages "asexual" (known as Marssonina rosae) and "sexual" (Diplocarpon rosae) whch is the most common.  Direct sunlight alone will not cure the disease although direct sunlight during the day is the best thing for elms.  It is also importat to not water the foliage while the disease is active on the plant.  Spraying with a copper based fungicide  or equivalent fungicide every 7-10 days for a month is the best solution.
 

yamins

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Re: Black spot on my Chinese elm
« Reply #10 on: June 30, 2011, 03:33 PM »
Ah so are we not seeing "Stegophora ulmea" (or e.g. gnomonia ulmea) on the elms?  ... Those are the things that normally come up on google when I search for elm black spot.   But upon further investigation the images don't like like what I've seen on my elms -- which does like more like diplocarpon infection on roses.    So  you're suggesting that diplocarpon also infects elms?

Is there any reason to think it will infect anything else, e.g. carpinus, pines, etc?   
 

plantmanky

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Re: Black spot on my Chinese elm
« Reply #11 on: June 30, 2011, 04:10 PM »
  So  you're suggesting that diplocarpon also infects elms?
Is there any reason to think it will infect anything else, e.g. carpinus, pines, etc?   

Yamins,

Yes, diplocarpon infects elms and is the most common disease seen on bonsai chinese elm  but there are others as well such as your Stegophora ulmea which is more often seen in wild elm populations and manifests with a canker like nodule on the leaves.  Along with roses, it will also infect Zelkova (a member of the Elm family) which is also a common bonsai subject.  It certainly is not found on Pines which are usually infected with simple black soot mold on the needles if they are getting too much shade and moisture on the needles.
 

yamins

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Re: Black spot on my Chinese elm
« Reply #12 on: June 30, 2011, 04:37 PM »
That's very interesting -- I can't find a single reference to diplocarpon infecting elms, but you're completely right, the infection looks identical and not at all like the stegophora infection pictures I've seen.    (Can you point me to a source of reference for this?)   
   
When I've gotten the spots on my elm (not this year, knock on wood), the defoliation/daconil treatment seem to work well.   But if it's the same as rose spot, this suggests that the diplocarpon-specific fungicides, e.g. the one made by Bayer, might be even more effective ...
 

plantmanky

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Re: Black spot on my Chinese elm
« Reply #13 on: June 30, 2011, 05:33 PM »
  (Can you point me to a source of reference for this?)   
   

Follow this link then click on "black spot" and it will link to the disease description.  By the way, the Bayer product works well fo black spot on Chinese elm.  It's very imortant to spray with limesulphur and horticultural oil as a dormant spray as I indicated above to keep the fungus under control
http://en.wikipedia.org/wiki/Ulmus_parvifolia#Pests_and_diseases