dying leaves on Japanese maple: water damage, drought, or disease?

Question

we had this Japanese maple placed last year by our landscaper, and it did well. this year it seemed to be doing well, but we just noticed these scattered branches with a bunch of curled leaves, and what looks to be dead branches. the branches affected may be the new growth, but i'm not positive.

we live in Chicago. tree faces south with partial shade. we've been using drip irrigation set to a timer. we turned the water off during our wet and cool june, but restarted it every 3 days for 90min in july, and then bumped it to every 2 days right before we left for vacation after forecast of a dry warm week. truthfully, we didn't notice the problem until we got back.

we sent this pic to our landscaper, who later looked at it through the gate and thought it looked like "drought damage". recommended to just keep watering it.

i'm not much of a gardener, but it didn't make much sense to me. we have a silhouette sweetgum tree a few yards away that's doing well, and none of the surrounding plants look like they're wilting or damaged.

i was originally worried that maybe we were overwatering, but i now understand 90min of drip irrigation should be okay (true?).

so, i guess i'm looking for a diagnosis and advice.

1. could it be drought damaged? should we worry about irrigation problem?
2. could it be sun damage?
3. could we be overwatering it?
4. is it diseased? if so, should we prune these branches before is spreads?

i'm hoping someone might be able to figure this out on sight. and since a picture is worth a thousand words...

(note the faded dry leaves and branches at the top of the tree, as well as the branch with red curled leaves to the left.)

thanks in advance, everyone!

Answer 1

Newly planted trees are not able to take up as much water as your well established sweetgum so it's a good idea to irrigate. The recommendations for Japanese maples are:

• moist, organically rich, well-drained soils in full sun to part shade.
• light sun dappled part shade.
• Avoid hot and dry sites. Leaves may scorch in full sun in hot southern summers.
• Plant in a location protected from strong winds.

I notice that all the damage seems to be closer to the wall which is cement with a white finish. I think the wall is reflecting heat and baking the new foliage.Leaf scorch is common on Japanese maples:

• irrigate more
• mulch to a depth of one to two inches (not as much near the trunk)
• examine the placement: it sounds like a hot south facing site that does not have enough shade

Just keep watering and see what next year brings. Where I live Japanese Maples are sold every spring but I never see a large specimen. They are fairly delicate where you get hot summers and cold winters.

Answer 2

To follow up, the disease progressed. After some research with our landscaper, we determined we were most likely dealing with the fungal disease "verticillium wilt."

although numerous references go into great detail, some of the very consistent features and general facts include:

1. sudden scorched appearance of all of the leaves on a particular branch, without falling off.
2. occurs late summer, july/august
3. tell tale ring when cutting off infected branches

generally speaking, this is not good news. the soil is affected and there really is no treatment, other than trying to remove as many damaged branches as possible, and see if the tree survives. it sounds like many trees don't end up making it, and the general recommendation is replacing the tree after it dies with a different species that is resistant.

also important is sterilizing any equipment with a 1:10 household bleach solution between cuts to prevent inadvertently spreading the disease to other susceptible trees or plants.

i just performed a fairly aggressive pruning project, as now nearly twice as many branches became affected as when i first posted. not sure if will make a big difference, but i wanted to give some followup up in case someone else stumbles on this post.

good luck

http://www.ct.gov/caes/lib/caes/documents/publications/fact_sheets/plant_pathology_and_ecology/verticillium_wilt_of_trees_and_shrubs_05-08-08.pdf