Crab Apple Leaf Blight

[Frax]

Four crab apples at a condo. One near dead, and 3 others nearby but on the other side of the street show leaf growth that seems stunted. Growth seems sparse on every branch of each tree. Image shows blighted leaves - at last I'm assuming its some kind of fungal blight. Leaves also with curled brown patches. Possibly related to our cold wet non-spring. Black winged aphids too but I'm guessing these are secondary.


leaf blight on crab apple by altacal, on Flickr

I'm going to troll through Sinclair and Lyon but all help appreciated.

 

[KTSmith]

Here's my usual disclaimer of trying to ID from a distant photo, but I'd start with "frogeye leaf spot" also known as Sphaeropsis leaf spot. A little time with a good microscope slide would clinch it quickly.
Diagnostic features include: host species and the concentric rings with a tan necrotic center and a purplish outer ring. As fall develops, you should get the tiny black spots or pycnidia in the tan center. Sphaeropsis is the asexual stage of Botryosphaeria obtusa.
More significant than the leaf spots themselves, is that they serve as a source of branch cankers on the same or adjacent trees. The cankers are commonly referred to as "black rot cankers".
Check it out in your reference books and see if it fits.

 

[Frax]

Thanks Kevin


I do believe you got it.

I looked in my 'scope and it looks as you describe. The images in Sinclair and Lyon look teh same as my trees too. I'm going to drive by this aft and see if I see branch cankers.

Thank you!

Can you tell me if its typically lethal.

 

[KTSmith]

Not usually lethal but the cankers can lead to canopy dieback and branch breakage. I think it is considered more of an orchardist problem than an arborist problem, except perhaps for cosmetics. The foliar infection does lead to premature leaf drop and a general unthriftiness, as a grower might say.

 

[SouthernTreeGuy]

Do you have any suggestions for treatment? Have a few with similar condition in SC and owner cherishes the tree, any thoughts would be helpful.

 

[KTSmith]

Sanitation is critical for managing this disease, meaning removal and destruction (as in burning rather than composting) of diseased foliage, fruit, and pruned branches with cankers.

How far you are willing to go with sanitation or other treatment depends on the crop. If it's simply a cosmetic concern, that's one thing. If one is a commercial fruit grower, that is something else.

There are likely fungicides available...check with your individual state ag folks. In SC, Clemson is a great source of information. For this disease, check out:
http://www.clemson.edu/extension/hgic/pests/plant_pests/trees/hgic2000.html

 

[RopeShield]

Strange or mb not so strange is any CrabApple planted with Taxus spcs shows low to moderate infection.

Proof is; same species, same enviro, same almost everything and the tree without Taxus companion was highly infected and with taxus=well below acceptable threshhold.

Food for thought or chalk one up for companion plants.

Just an observation I made years ago and try to be aware of day to day in the field.

Trees have developed over their history with companions and if these companions are missing it is likely health and vigor is lacking. Most likely all levels of life are involved from the micro to macro biota.

 

[Frax]

Well, its a reasonable hypothesis RS. the apple - cedar rust and juniper - hawthorn rust show this relationship.

No taxus here though. Or should I say quite rare. But I have also not seen this infection befoore either.

 

[KTSmith]

Thanks RopeShield, I hadn't heard that observation! You bet, what we don't know is far greater than what we do know!

 

[RopeShield]

Two more interesting ones from the other day on the same property.
Siberian peashrub and Tomato. Tomato plant was enormous with mb 1" or more dia stem.
Beautifully healthy Cornus mas growing just outside the dripline of the Honey locust. It is also fruiting encredibley this year.
Root nodule bacteria can fix enough nitrogen to secrete excess nitrogen/ammonium into the soil.

Rhizobium, Companion planting for phytochemicals, plant hormones, mycorrhiza, etc
A read a book years ago "The Secret life of Plants". I remember it vaguely. I should revisite it. It was the reason I got into plants in the 1st place.

There are techniques for cover cropping a struggling tree to improve soil and inturn tree vigor.
Orchards do it so why not for a troubled planting of Crabapples. Mb overseeding with clover and Alphalpha.

 

[Frax]

Complete derail but I agree and its my thread so continue on! I think that the fact that peas (Fabaceae) fix nitrogen goes underused as a strategy. Eastern aboriginal tribes made use if this when planting "the 3 sisters" corn squash and beans. And before we had to find a use for vast quantities of war materials rebranded as chemical fertilizers clover was added to grass seed mix on purpose.