Linden tree leaves dropping

Asked August 27, 2017, 7:28 PM EDT

Hello,
We have a five year old Linden tree that's showing signs of problems. But I can't tell if its stress, pests or a fungus. This is the first year since we've planted it that it looked great, had full branches and lots of new growth... until the first few weeks of August. Suddenly, it looks like several branches are dying. Leaves are turning brown and dropping. There are lace like holes on some of the leaves, which made me think of Japanese beetles or caterpillars. But I haven't seen any. There is also some black spots on some leaves. And marks on the trunk. Any advice would be greatly appreciated!

Oakland County Michigan

3 Responses

Hello,

Thanks for the pictures. The leaf damage could be feeding from beetles or chafers. It is cosmetic and the tree can recover from that.The holes in the trunk are the most urgent sign that something is wrong. There are a number of borers of linden including linden borer, redheaded ash borer, ambrosia beetle, and plum borer. Most of these insects are attracted to stressed trees. Since your tree just returned to normal growth, it has been stressed for some time. I also see that the tree was planted too deeply- the trunk goes straight into the ground with no root flare( a.k.a. Root collar) at the soil level. This restricts the amount of oxygen that the roots can receive, stresses the tree and shortens its life.

Another stress on trees is too little water. During droughts, like we are having right now, the tree needs slow deep watering so that roots are moist at least 12 inches down.

I recommend consulting a certified arborist to confirm the presence of borer insects and the best treatment. You can find them here by zip code- www.treesaregood.org

What you can do now is- keep the tree watered up to when the ground freezes this fall; attempt to expose the root flare by gently excavating the soil around the trunk - this may be several inches down; mulch around the root zone(don't let mulch touch the trunk or root flare); consider using a tree insecticide drench to control the borers - if you do not consult an arborist. If you do consult an arborist he/she will determine if insectidie is required and give you a tree care plan. Note that if you use insecticide you should move any edible plants away from the area for that growing season. Also, I would avoid using insecticide in spring when the tree is in bloom, since bees and other beneficials are frequent visitors to linden flowers. Wait until next spring to see which limbs are really dead before pruning them off, unless your arborist says otherwise.

Here are some links that explain the root flare, correct pruning, and proper watering of trees. In the "Tree Owner's Manual" see pages 13, 15 and 16.

http://msue.anr.msu.edu/news/tree_owners_manual_now_available

http://msue.anr.msu.edu/news/drought_conditions_begin_to_impact_michigan_landscapes

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Laura,

Thank you for all the information. We exposed more of the trunk flare (it was planted by a landscape company...but I should have noticed that sooner!) and I went to buy some general insecticide today but the only one I could find said "do not use on linden trees". I believe it was the Bayer Advanced brand. Is there an insecticide that you'd recommend?

Thank you!!
Teresa

Hello Teresa,

I am glad you read the label! Yes, if it says not to use on linden trees I would not.

According to my references Linden borer, and a wide variety of other insects, can be controlled with imidacloprid. I don't know why your label prohibits lindens, but you can call the 800 number on the label and ask them.

Another chemical listed for common borers is dinotefuron. This is available to homeowners as a granular product for trees. Note that you do not want to grow anything edible near this product. If you google search "dinotefuron granular", you will find products available. (MSU Extension is not allowed to recommend brands or retailers.) Many products now have their labels online so you can read them before making a trip to purchase the product.

Here are References for borers that affect linden trees:

https://www.extension.umn.edu/garden/insects/find/bronze-birch-borer/

http://cues.cfans.umn.edu/old/Web/164LindenBorer.pdf

http://byf.unl.edu/cd861c9e-0c8d-4133-97c2-76d2a0e20332.pdf

As a reminder, we do recommend you get a positive diagnosis before using any chemical.

Thanks, again, for using Ask an Expert.