Yellowing big leaf maple leaves - Ask Extension
Hi team of experts! I planted two young big leaf maples in my Portland yard last fall. They got off to a good start this spring, but leaves are turnin...
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Yellowing big leaf maple leaves #764977
Asked July 31, 2021, 4:46 PM EDT
Hi team of experts! I planted two young big leaf maples in my Portland yard last fall. They got off to a good start this spring, but leaves are turning yellow. In response to the unseasonably warm days (high of over 100 a few weeks ago, 85+ every day for the past 60+ days, no natural precipitation) I have been soaking them once a week for 60 minutes or so, in addition to the regular drip irrigation they receive almost every day. In researching the problem, some suggest a lack of iron in the clay soil, or inability of the trees to take up the available iron in the soil. Both trees seem to be affected, one somewhat worse than the other. They are situated about 20' from each other, receive about same sun/water, soil conditions should be identical. I really appreciate your willingness to help!
-chuck
Washington County Oregon
Expert Response
Hi, Chuck,
Bigleaf Maples are one of the trees that have been suffering in recent years. Here's an article from the Department of Forestry about their decline.
Some of the damage on your trees does look like heat/sun exposure. In addition to watering, you could shade them on particularly hot afternoons and add mulch (though it looks from the picture like you have already added some mulch). It also looks like the tree with more yellowing might have had some insects sucking on its leaves, possibly leafhoppers. If so, that could have something to do with the decline (see article linked to above).
There's also a possibility that your trees have Verticillium Wilt, which is caused by a fungus in the soil. There isn't really an effective treatment other than keeping your trees in good vigor, which is difficult in young trees with the weather we've been having. You don't need to remove the trees right away since this fungus is common in the soil and you won't get rid of it by getting rid of the trees anyway. Work on giving them the conditions they need and they may recover.
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. Here's one in our area. Instructions for how to take the sample are at the link. Make sure to tell them what plants you are concerned about and they'll give you suggestions on what nutrients to add if they find that some are lacking as well as how to adjust soil pH if necessary. (Improper pH can make it so that plants can't access nutrients even if they are there in the soil already.)
Finally, it may be that they are being overwatered. Try digging down 6-8 inches in the soil just outside their root zones (so as not to damage roots) and make sure the soil is just moist and not soggy. If you find that the soil is drenched, let it dry out for a week and test again. In this case only water when the top 6 inches or so are mostly dry and then water deeply.
Bigleaf Maples are one of the trees that have been suffering in recent years. Here's an article from the Department of Forestry about their decline.
Some of the damage on your trees does look like heat/sun exposure. In addition to watering, you could shade them on particularly hot afternoons and add mulch (though it looks from the picture like you have already added some mulch). It also looks like the tree with more yellowing might have had some insects sucking on its leaves, possibly leafhoppers. If so, that could have something to do with the decline (see article linked to above).
There's also a possibility that your trees have Verticillium Wilt, which is caused by a fungus in the soil. There isn't really an effective treatment other than keeping your trees in good vigor, which is difficult in young trees with the weather we've been having. You don't need to remove the trees right away since this fungus is common in the soil and you won't get rid of it by getting rid of the trees anyway. Work on giving them the conditions they need and they may recover.
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. Here's one in our area. Instructions for how to take the sample are at the link. Make sure to tell them what plants you are concerned about and they'll give you suggestions on what nutrients to add if they find that some are lacking as well as how to adjust soil pH if necessary. (Improper pH can make it so that plants can't access nutrients even if they are there in the soil already.)
Finally, it may be that they are being overwatered. Try digging down 6-8 inches in the soil just outside their root zones (so as not to damage roots) and make sure the soil is just moist and not soggy. If you find that the soil is drenched, let it dry out for a week and test again. In this case only water when the top 6 inches or so are mostly dry and then water deeply.
Larina,
Thank you for the thoughtful note. Really too bad to hear that big leaf maples are suffering. They are beautiful and essential trees. I will look into the possibilities you propose.
Thanks again for taking the time to help me and my trees.
-chuck
