chinese elm black spot?

watchndsky

All of my elms were doing great - explosive growth agian this season, etc. Pruned back course growth to shape - when I started noticing the yellowing of the leaves. I was pretty sure I wasnt overwatering, (and its been pretty dry around here anyway) To me it didnt seem to just be old growth dropping either.

So I checked for any signs of pests - saw no signs and read up on black spot. Ive never had this problem before - but I read the article of blackspot fungus, and realized I had been guilty of watering thru the foilage as the new growth was coming out - a real no-no. So I thought this was the problem.

I applied two round of daconil (waiting to apply the third), all but two trees seemed to be stable (I had removed the yellow or fallen leaves when I applied the fungicide)

But those two trees (which are the the oldest with nice thick trunks unfortunately) seem to be continuing to yellow etc. Any ideas? Did I misdiagnose? I had read that after being infected they might not look so great for the rest of the season, but to me, they dont seem to be responding to the treatment. There isnt any dieback on branches (yet) but Im worried because these are my favorite elms that i have. They still have a little new growth on them but they are looking pretty bad - and they have always been very healthy.

Am i too impatient - should I be concerned? Or continue to wait it out. Im afraid Ill have dieback in the branches etc, and lose some of the shape.

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watchndsky

Alot of the leaves are yellow but some are green with the balck spot. Some of the leaves are simply yellow or yellow with green spots. However, most have the black spots on them that are dull and dried out looking.

bonsaimeister

Maby this will help
It was written by thomas J.

One of the biggest problems with chinese elms is their tendency to get Black Leaf Spot, an awful fungual disease that will do serious harm to your tree if it's not treated ASAP. This disease starts its life in the Spring when the new leaves have started opening and the Spring rains are quite often. It only affects new tender growth that hasn't hardened off yet. After the leaf has been infected it will follow through to the branches making them look like they've been burnt at the tips and cause them to shrivel up. The tree naturally is under significant stress because of this. If steps aren't taken to completely eliminate the fungus, the tree will probably die. Even after treatment begins the damage will probably last throughout the rest of the growing season. A serious treatment with an antifungual must be started immediately, and a watchful eye to see that the disease is being eliminated during the course of the treatment. A product called Daconil is a good one to use for this. Use it by drenching the crown of the tree and work your way down so as to wet all leaves; those that are infected and those that are not. Do this with your watering can.
All this trouble can be eliminated though in most cases, by not doing one specific thing, and that is to not water the new leaves until they harden off. This will probably around six to eight weeks form the time they open. Once you notice the color of the leaves turning from light green to to bit of a darker green, and they don't have that tender look to them, you should be safe. And when I say no water on the leaves, I mean no rain water also. That means if you know that rain is in the forecast, you must do whatever you have to to shelter it. Sounds pretty drastic I know, but this simple precaution will eliminate a lot of trouble later on. If your tree should come down with this disease, continue to fertilize as usual even during treatment to allow the tree to bear the stress that it will be going through. As I said the damage will remain throughout the growing season, but next Spring should have the tree showing no signs of what it went through the preceding year.

hope this helps,
bonsaimeister

__________________
"On its root I firmly commit
In its trunk I keep my soul
Through its leaves, I reflect my vision..."

- Robert Steven

watchndsky

Thanks I had already read that and read through BT forums for chinese elm yellowing.
I guess what Im asking is did I diagnose/treat this correctly (4 of 6 trees seem to be stabilized and no longer yellowing dropping etc)
The other two (the nicest ones) dont seem to be rebounding very well are continuing to yellow and drop leaves.
The only thing that made me doubt it was not black spot was that partiuclar article said that it affects new growth only and this was new and old growth.

watchndsky

Any suggestions? Wait it out?
I checked the soil - it doesnt appear to be breaking down either, no funny smells etc.

DrDirt

How often are you watering, and is the soil staying saturated?

watchndsky

Mostly every other day - depending on the temps. Sometimes daily. I never let the soil dry out completely but its not so fast draining that I have to water every day either.

I watered the same in the past with no ill effects, so I really wasnt thinking that it was being overwatered. Do you suspect that fungus isnt the problem?

ALDEVAUX

The spots shown on your pics definitely look like leaf spot of elms caused by Stegophora ulmea.
It is not true that these spots do not infect old leaves although the younger leaves are definitely much more susceptible. There are also different strains of the pathogen, the inported one being most aggressive on young elm shoots. Some strains attack mostly older leaves.
The normal control for this disease is to apply fungicidal sprays early in spring, and before rainy periods because the fungicides can only protect healthy tissue and do not eradicate existing infections.
As in your case, when infections have occured before fungicidal applications, you should not expect infected leaves with visible spots to become normal. Many of the leaves which do not show visible spots could also be already infected because they are not visible during early stages of infection and they will eventually show up even after fungicides have been applied because the fungus is inside the leaf where the fungicide does not go.
The only thing that the fungicide can do is to protect non infected leaves to be infected by the fungus as it kills the spores before they can germinate to enter inside the leaves. In other words, the fungicide is effective only as a preventive measure.
The best way to protect non-infected leaves is to to use a sprayer that will deliver a very fine mist that will cover completely both sides of the leaves especially the undersurface where most infections take place. This is the kind of complete coverage you will observe in orchards when they are sprayed to protect the trees from fungal infections. Spraying with a watering can is innefective and a waste of the fungicide.
Furthermore, the sprays should be renewed every 15 days, or earlier when the leaves are wet, until all the new leaves do not show anymore infections.

watchndsky

EXACTLY what I was looking for!!!! Thanks for the confirmation.

Since the that particular tree continued to "get worse" - I was starting to wonder if I was wrong in my diagnose or if leaves would continue to fall off that had already been infected prior to treatment but were just not showing the signs at the time of treatment.

I appreciate the help!!!