Help with a sick tree #595456 - Ask Extension


Help with a sick tree #595456

Asked September 08, 2019, 9:05 PM EDT

Hello, I live in Denver and over the past few weeks, my tree has developed something affecting the leaves. Can you tell me what it is and what I can do to make the tree healthy again? Thank you so much for your help!

Heather Feigelson

Denver County Colorado

Expert Response

That looks like a red Oak and the spots may be from heat stress and lack of sufficient moisture. The photo, however, is dark and it is hard to make a diagnosis from it. It would be helpful if we could see a stem with leaves in better light and also a photo of the whole tree that shows the base and surrounding area.
Gardening Help Replied September 11, 2019, 12:37 PM EDT
Thanks. Here are some more pictures 
The Question Asker Replied September 11, 2019, 6:00 PM EDT
Thank you for those; they are helpful. The lawn under your tree looks very green and healthy which suggests that despite the recent hot weather you have been applying supplemental water to the area.

Your tree is chlorotic, a term which describes a plant's inability to uptake enough iron (or other nutrient). This is a common condition in Colorado's alkaline soils. It starts with the leaves yellowing but can advance to browning and dieback. Read more about it here: We see it more often on Pin Oak (Quercus palustris) but less often on other species of Oak. I'm wondering if in your case, your soil is very clay-ey with poor drainage and watering the turfgrass has resulted (or worsened) the chlorosis in the tree.

The tree is going to drop those leaves in another month so I would recommend that this fall you work on getting rid of the lawn around the base of the tree in an approximate 5' diameter circle. That way mowers/weed wackers won't nick the bark and cause wounds - sure death to trees. Replace the turfgrass with a couple of inches of shredded wood mulch but make sure the mulch isn't touching the trunk. You want the mulch to cover the roots, not rest against the bark.

This fall after the tree goes dormant, give the tree a good soak to better prepare it for winter weather events. Then concentrate on watering it once a month through the winter if there is no snow cover/precipitation and the ground isn't frozen 

Next spring, keep your eye on the weather and don't overwater the area which can make chlorosis worse. Also next spring you can try applying a chelated iron product to the rooting area which may help.

Gardening Help Replied September 12, 2019, 1:07 PM EDT

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