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curling leaves on Ash and Oak Trees and brown circles with green centers in lawn #424012

Asked August 29, 2017, 12:53 AM EDT

Hello, I have few different things occurring in my yard I could use some advice on. I have 2 - 15 year old Bergeson Ash trees that have always done well in my yard, but both seem to be thinning and the leaves are curling this year. I've included pictures. I also have a young Oak tree that is losing it's leaves. It does this every year at this time and I suspect it may be getting overwatered. Both the Ash trees and the Oak is in an area covered by my sprinkler system and I have been watering daily. Finally, once again this year in late summer I am experiencing brown circles with green centers in the lawn. Most of the lawn is really thick except for these spots. I do have a lawn service that applies 4 fertilizer applications per year. I haven't done a soil sample before. The last time I aerated was approx. 5 years ago. I suspect my soil may be pretty compacted and it is bumpy in certain parts of the lawn. The mature trees in the yard are doing well (mixture of large Oaks and Ash trees). I live in the River Oaks development of Horace, ND. Thanks for any advice you can provide! 

Cass County North Dakota

Expert Response

Good afternoon,

I think there are several things going on, and I'll do my best to answer them. 

First, regarding the ash tree, it has been under stress for at least 3 years, maybe 4.  Something happened to this tree in late 2014, I believe, and it has done poorly ever since.  I can tell this by the amount of growth on the twigs for the last 3 growing seasons. The thinning and curling leaves are a symptom of whatever long-term stress this tree is under.  It could be overwatering, it could be that it was planted too deep, or it could be that it had fill soil added over the root system 3 years ago.  Or even something else.  So, you will first need to figure out what the initial stress was from 2014, then try to alleviate that.

The growth on the oak looks okay, but not great.  I noticed that the lawn in the background is very full and lush.  I'm wondering if this tree has received some herbicide damage, possibly from chemicals used to control broadleaf weeds in the lawn.  It's hard to say for sure.  The bumps on the twigs are from the bullet gall wasp, a tiny insect that's usually harmless to the tree.

Both these trees could do with less watering.  Trees generally don't need watering unless there's been no rain, and even then, watering every 10-14 days should be enough for a mature tree.  Also, adding a lot of fertilizer can also cause problems for trees.  Specifically, if trees are growing extremely vigorously going into fall, they likely won't completely harden up for winter and will get damaged from the cold weather.  Generally, I recommend no watering for the month of August and no fertilizer after (about) Independence Day.  Of course the lawn won't be as lush, but it will reduce long-term stress on the trees.

I don't know what's happening in the lawn, as I'm not a turf expert.  I know that my colleagues often mention that spots like this in a lawn are often from dogs urinating in an area.  Could that be what's happening here?

Best wishes with your trees,

An Ask Extension Expert Replied August 29, 2017, 2:49 PM EDT
Thank you very much for the thorough and helpful explanation. I will plan to decrease watering and reduce the lawn fertilizing next Spring. Is there any chance Aerating around the Ash trees could help? This morning I also noticed some green moss growing on the north side of one of the Ash trees.
The Question Asker Replied August 29, 2017, 9:40 PM EDT

Aerating is not usually needed for trees, unless the soil has become compacted.  Decreasing the watering should actually increase the amount of air within the soil system.  That being said, aerating will not hurt the tree either.  I just don't know that it'll help.

Sorry for such a wishy-washy answer.

An Ask Extension Expert Replied August 30, 2017, 7:48 AM EDT

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