Help my poor magnolia!

Asked June 30, 2019, 12:01 PM EDT

Dear OSU Extension, I bought an Elizabeth Magnolia from Friends of Trees earlier this year and it isn’t doing so well. I’m guessing it might have some sort of fungus, which has left black spots on the leaves and veins, and has yellowed some of the leaves more than the newer green growth. I’ve sprayed it twice in the past few weeks with a copper fungicide but don’t know if it’s the right approach. My mother-in-law is an avid gardener and simply suggests I should cut it down and start over since rust/fungus is such a pain and another tree or another variety might be more resistant. That’s not my ideal solution though. What do you think is happening and can you please help my poor magnolia!? Yours, Perturbed in Portland

Multnomah County Oregon trees and shrubs magnolia

3 Responses

Thanks for you magnolia question. It may have a fungus (though it doesn't really look like one), but that is not the primary problem - the yellowing leaves look like a severe nutrient deficiency. Since this is a newly-planted tree, it may not have a well-established root system yet. But, if you have not tested your soil, I suggest you do so to see if it is lacking something - quite possibly Nitrogen, from the look of the leaves. Once your tree is established and getting the nutrients it needs, chances are it will fend off any other problems easily, so I recommend giving it another chance. You may need to wait until it puts out new leaves to see a real change in appearance.

Thanks for your response. I’ll get my soil checked and use some fertilizer in the meantime.

One question though, I’ve got the tree pretty heavily mulched with some woody debris that I chipped last year. I’ve heard that chips can sometimes rob nutrients from the soil. Is that true and should I be worried about that possibility here?

Wood chips on the surface of the soil, as mulch, are actually very good for the soil, and take little N from it. However wood chips mixed into the soil can indeed tie up N, as the microbes in the soil work to break down the chips. If your soil is already N deficient, then even chips on the surface might be contributing to to the stress your plant is under, but I would not advocate removing them - they do a lot of other good things for the soil like hold in moisture, reduce weeds, minimize temperature fluctuations, and gradually break down to improve it. Just add fertilizer, preferably a slow-release organic one, and wash it in well. You could pull some mulch back in spots to dig some of it in - getting it into the soil will make it available to the roots faster.
Here is a WSU publication on wood chip mulches if you are interested. https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=22&cad=rja&...