Hi Jennifer,

Thanks for your message. Unfortunately, die back in bigleaf maple is being seen all over our region and is associated with higher temperature and drought (+ associated vapor pressure deficits). Symptoms of dieback include premature yellowing of leaves, thinning and entire crown dieback. Branches sometimes have clumps of unnaturally small leaves and heavy seed crops. Leaves may have edges that resemble leaf scorch. I've linked a resource below that talks about this in a bit more detail. Sometimes, drought-stressed trees are more susceptible to pests and pathogens as well.

Deep and infrequent watering may alleviate symptoms during exceptionally hot and dry weather. A fresh, thick layer of bark mulch around the base of your tree can protect it from lawn mower damage as well as keep moisture in the soil.

Something to note is that by the time several of these symptoms are seen, it may be too late for watering to be influential. At this point, you may consider species that will do better in these conditions, like Oregon White Oak or Incense Cedar.

Do you notice anything else going on with your bigleaf maple aside from yellowing leaves? Please feel free to send me photos. This will help illuminate what steps you may be able to take.

Hello Lorelle,

Thank you for the quick response although it is very disheartening. I am attaching a few photos. The first picture is the same tree in Aug 2023. It was lush, full and green and beautiful all throughout last summer. I did wonder, even last year if the leaves were the right size. They were not a full dinner-plate size even last year. Now they are still large, but not huge like I remember them in the past. The tree leafed out fully this year and then rather quickly yellowed up this summer. I am stunned at how fast the change has occurred.

About a month or so ago I noticed there was a powdery look to the leaves. But I saw that on the Big Leaf Maples up in the McDonald forest as well. Then early last week as heat wave was coming we took stock around and I noticed the yellowing leaves and profusion of seeds on this tree. So we gave it a good drink. Now in just over a weeks time the yellow leaves have browned and most have fallen. This week the tree looks visibly thinned out. It is worse on the south side of the tree.

Can you please be more specific about the watering recommendations? What we have done with large trees in the past is run a sprinkler on low for 2 hours once a week. Or put 4 or so 5-gallon buckets with a few holes, filled with water around the base to try and do more drip style. We are not sure what the right amount/method is for a huge tree. Please advise. We will switch from mowed grass around it to compost mulch if you think it may still help when you see the photos.

We would really like to save this tree. Any other suggestions for help, or recommendations for who can help would be very welcome. We contacted a tree service last year about another tree and were never able to get them to come back out to apply the nutrition they recommended. So I am at a loss for who to reach out to with this tree.

Fyi.. when I was looking up what to do I saw this article from the extension service in 2007. First off it recommends Big Leaf Maples as a native water-wise tree. I wonder if anyone would recommend them now? Less than 20 years ago. https://extension.oregonstate.edu/news/many-water-wise-trees-are-available-home-gardens

Can you please reattach the link you recommended? I do not see it.

Thank you again for all your assistance.

Jennifer

Here are 3 more photos from yesterday.

Hi Jennifer,

My apologies for not properly attaching the link! I've made sure to do it this time. Given that the tree is out in the open surrounded by field on most sides, I suspect the heat and drought in combination with other pathogens is stressing your bigleaf maple out. Although this is the leading theory for the region wide bigleaf maple decline, we aren't 100% sure what is causing the decline in western WA and OR. I've linked a study on the decline below. It looks like the leaves have powdery mildew on them, which is common in our area after a prolonged wet and cool spring like we had this year (see link below). Powdery mildew does not seem to be major cause of dieback in bigleaf maple. 

If you want to check and see if your trees are lacking nutrients, you can take a soil sample and submit it to a lab. If you want to go that route, I can locate the nearest lab to you. I've included a couple of links on tree watering below.

I'd say these are your options:

•  supplemental watering in time of extreme heat and drought
• mulch a wide heavy ring around the tree base (3-4') while keeping the mulch pulled back from the tree bole itself (not piled against tree)
• keep live grass away from the base of the tree as grass can suck quite a bit of water from the soil, possibly exacerbating the tree stress
• make sure no herbicides are used anywhere near the tree (especially ones you'd use to kill weeds in grass)
• submit a soil sample to a soil lab to make sure nutrient levels are sufficient

OR Dept of Forestry "Why is my bigleaf maple dying?": https://www.oregon.gov/odf/Documents/forestbenefits/tree-declines-bigleaf-maple.pdf

Powdery mildew on bigleaf maple (and how to control it): https://pnwhandbooks.org/plantdisease/host-disease/maple-acer-spp-powdery-mildew

Study on bigleaf maple decline in western Washington: https://digital.lib.washington.edu/researchworks/handle/1773/43386

Watering mature maple trees (with additional links inside): https://ask2.extension.org/kb/faq.php?id=802962

OSU Extension Watering tips: https://extension.oregonstate.edu/sites/default/files/documents/12281/wateringtips.pdf

I hope this helps! Please let me know if you have any additional questions.

Excellent help Lorelle, thank you. This tree provides much needed shade for us so we are going to take all the steps you suggested. Please do send the info on the nearest lab for soil samples.

Thank you again,

Jennifer

Hello again Lorelle,

You have been a great help so far. One last question (I hope).  This one is clarification about mulching under the tree for relieving drought stress. As I understand it, the articles on irrigating a tree say that it's important to water it at, and even a bit further beyond the tree's drip line.  We are willing to put compost around the tree. So, our question is how big a circle of mulch around a tree this size is optimal to reduce drought stress? Would it be more beneficial for this tree if we replaced the grass surrounding it with a thick layer of mulch to cover the whole area within the drip line? Seems like it would be better to add mulch a lot further out than 3-4 feet. I think it would take about a 30 foot diameter circle of mulch all around this maple to cover inside the drip line.  We would weed whack the grass down short and put one layer of newspaper under the compost. It's an expense for the compost but it seems like it would be the best way to limit the water competition and efficiently get the irrigation to the tree's roots. Again, we are willing to do quite a bit to keep this tree.

Please let us know your thoughts on that last point. Thank you, Jennifer

Hello,

It's hard to say exactly what will and will not work as this is a novel issue associated with a combination of environmental factors. The bigleaf maple decline is a recent issue and is still being studied by researchers in western Oregon and western Washington. I will say that you are unfortunately not alone and there are many reports of bigleaf maples quickly losing their leaves after they turn brown. I actually went to a park this morning with a forest pathologist to examine 3 bigleaf maples that shockingly quickly lost all of their leaves and they could not find any conclusive pathogen or pest and instead cited abiotic factors, such as heat stress. All I can say with certainty is grass can rob large amounts of water from nearby trees, so it may be wise to kill the grass around your tree with cardboard/mulch and try supplemental watering in hopes that this gives your maple the extra push it needs to survive.