Magnolia tree - insect death

Asked May 20, 2019, 4:51 PM EDT

I have a magnolia tree in my yard, which I estimate is at least 25 years old, that has died this year. I contacted someone at MSU last year but lost the emails and messages (I have reattached images I sent last year, I suspect you may be able to find the old emails?). I was instructed to send in branch samples, but considering the tree lost 95% of it's leaves last July - I opted to wait until this spring to see if it would die. I hold a PhD in animal science from UCONN and have taken multiple courses in botany, mycology and plant science. My understanding, and based on my research, is magnolias are not typically prone to boring insects and therefore the death of this tree is somewhat surprising and alarming. The tree has some apparent rot near the truck, but also appears to have damage from a boring insect. I found no evidence of scales. Given the harm of the ash borer and various other parasitic insects on the Michigan forests - would the MSU extension like to examine this tree to gauge potential harm to the surrounding areas (i.e., potential pest migration) before I remove it? My wife currently has a few bird feeders and a bird house (occupied by wrens) in the tree, and therefore I don't plan to remove it until sometime this summer (late July or August). Please let me know if you'd like to inspect the tree and/or collect tree or soil samples to identify the cause. Looking back, this tree died in waves over 2 growing seasons. The attached pics show the trunk damage, a clear picture of the boring holes, and the top of the crown taken last September (when the tree should have been in full leaf). My house is located in Cooper township less than 5 miles from the Allegan Co. line. Thank you. Sincerely, Chris Keator, PhD

Kalamazoo County Michigan insect damage magnolia

6 Responses

Hello. MSUE does not typically make house calls for issues like this. I suspect your tree succumbed to either verticillium wilt or phytophthora, a root rot. Are you familiar with these? The holes are probably secondary to the death of the tree. When you remove it, cut into the branches and trunk and look and see if there are darker rings which usually indicates verticillium.

Hi Marcia,

Thank you for the response. It may be verticillium wilt, the tree was definitely stressed and exhibited symptoms consistent with wilt (leaf scorch and last season produced a heavy amount of seed). I was more concerned that we have a new parasitic insect to deal with, and we have enough of those to already deal with on a regular basis.

My understanding is that this fungus this will persist in the soil for many years and the best way to deal with it is to simply plant a resistant species. We have a large amount of mycorrhizae in the mulch and soil in the flower beds (surrounding the tree and nearby areas) and therefore suspect there is a high load of soil fungi.

Do you have any recommendations for a replacement flowering ornamental tree, a species that would be naturally resistant (not engineered) to the fungus and grow well in SW Michigan?

The one flowering tree that shows up in lists of resistant trees is dogwood. The tag on the tree should say if it is a verticillium resistant type. It is important not to damage the new planting in any way, such as from lawn mowers or string trimmers or mulch right up to the bark of the tree. . Injury can give the disease an entry point. Also, do not use any wood chips that may come from the dying tree. Remove all the debris.

Thank you!

After doing some additional research, I believe the bug damage is from a shothole borer (https://www.canr.msu.edu/ipm/diseases/shothole_borer ).

We have a large number (20+) of apple, pear, peach and cherry trees on the property. So, although I don't see any borer damage on those trees, it's obvious they're on our property and now I'm worried about my fruit trees.

Based on the information I could find (in addition to the MSU sheet), it appears the borers are quite difficult to kill (based on emergence, lifecycle and size), but are there any any products that I can/should apply to the fruit trees?

All the fruit trees are healthy, but is there any treatment that you can recommend for this summer? I've only sprayed these trees once (the first spring we lived there, in 2015) and therefore the fruit is organic, but I'm more concerned about preserving the trees. I'm considering the use of a dormant oil in late Fall to smother any insects that may try to overwinter (but that doesn't help me during this summer).

The crucial element of the shot hole borer is that it’s usually found in dead or decaying wood. If this insect is present it probably appeared after the tree became stressed. I will forward your question to a fruit educator.

I don't think this is shothole borer on the magnolias. The beetle is very tiny and makes holes about 2 to 3 mm in diameter.

Regarding the fruit trees, there are not any effective trunk insecticides available for the homeowner. I would recommend examining the base of trees and crotches of large limbs for gumming. If gumming is seen, use the point of a knife or small screwdriver to probe for burrowing larvae. Kill the larvae, if found. This is an old time method of control used by fruit growers.