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Colimner Silhouette Sweetgum really need Agri-Fos treatment for Root Rot? Is it something else? #750777

Asked May 19, 2021, 4:49 AM EDT

Just started in PHC work and am taking over a new client's landscaping property. There is a circle of slender silhouette colimner sweetgum in the back yard in a mulch bed. The previous treatment recommend from their previous PHC specialist was Agri-Fos for root rot. But as far as I understand this variety of Sweetgum tend to be relatively resistant to fungal root disorders, and borer pests. It is in semi-clay soil, and not under shade. They have fissures that look kind of like winter damage, and the one has that old wound that doesn't look great. The pictures were taken 5/11/21 with a lower than average GDD 145 BASE 50, right after the last freeze warning for the year. There are Magnolias growing very close by, in the same conditions, that are doing very well. Scale didn't even need to be treated this year, they look so good. Surrounding boxwoods look great too. Not sure if the Agri-Fos is a up-sell from the last PHC company, or if I am missing the underlying signs of disease/pest. Hope you can give me some insight. Thanks!

Kent County Michigan

Expert Response

Here are some possible issues with your client's Liquidambar styraciflua "Slender Silhouette."

These trees are rarely attacked by pests, but bleeding necrosis, a fungal disease, can occasionally be a problem. When infected, the tree will look like a can of oil has been poured on its bark at the soil line. Although there is no known treatment, experts believe that raising the soil grade around the tree fosters this disease.

They will not tolerate alkaline soil. Have you conducted a soil test? Self-mailer soil test kits from the Michigan State University Plant and Pest Diagnostic Lab are available. You can obtain them at the link below. Full instructions are there and also come with the kits. The cost is $25. The Lab will make recommendations for any needed soil amendments.

https://shop.msu.edu/product_p/bulletin-e3154.htm

In addition, these trees are not hardy in the northern areas of Zone 5. They are native to bottomlands and moist soils and tolerate only some (if any) drought. Existing trees often dieback
near the top of the crown, apparently due to extreme sensitivity to construction injury to the root system, or drought injury. Just looking at where these trees are growing, I would believe they may not be getting enough moisture.

An Ask Extension Expert Replied May 20, 2021, 1:14 PM EDT

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