Mystery tree spreading itself all over yard

Question: Hello. This tree is sending up shoots all over our yard, and they are especially numerous and widespread this year. It appears that the shoots come up from roots already spreading throughout our yard. I would like to know what kind of tree this is, and how to eliminate and prevent the shoots it is sending up everywhere. Cutting them back just seems to cause an even greater number of them to soon sprout.

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied June 23, 2023, 3:26 PM EDT
response: These look like alder tree leaves but I didn't realize they spread like this. Dig one up: are these separate seedlings, or connected to the large root system (meaning they are suckers). Shoot me a photo or two of the whole area, including the crowns of trees. Do you know which tree is the "mother" of these problem plants? This article on unwanted vegetation from OSU Extension covers covers herbicide application methods. Do you want to remove the whole tree with all the unwanted suckers? Keeping the tree and removing suckers is more challenging. From this University of New Hampshire page: "Unlike water sprouts, suckers should be removed as soon as they appear. Once suckers start developing on a tree they will usually continue to occur for the rest of that tree’s life and will need to be removed regularly. Suckers that grow up in lawns are easy to manage with a lawn mower; those that grow from the base of the trunk or from roots in landscape beds will need to be removed by hand. Ideally, they should be cut back to the point where they emerge from a root or the stem, as leaving a stub can make the problem worse by causing multiple shoots to form. Removing suckers that arise from roots may require a little digging. There are products for sale that contain synthetic auxins (NAA) that are labelled to control sprouts on certain trees. Unfortunately, little research has been conducted on their effectiveness on landscape trees. Similarly, some herbicides have been shown to be effective at controlling and suppressing suckers, but they are not recommended for use on ornamental plants. Herbicides applied to suckers have the potential to harm the parent plant."

responder: The Question Asker Replied July 20, 2023, 1:18 AM EDT
response: Hi, thanks for the info. Sorry about my delay in responding, but things got really busy during the first half of July!The sprouts are definitely coming from roots of the tree that have apparently spread all over our yard! I see in the article you sent that such sprouts need to be cut off all the way back to the root, and I did not know that, so earlier this spring I just mowed them off close to the ground but not all the way to the root. That must be why I have been overrun with new sprouts.There are actually two very large trees along our property line that are likely the mothers of these sprouts. I would love to get rid of the trees and the sprouts, but a tree service quoted me around $5,000 to remove both large trees, so we have not taken action on that.I am attaching a photo of the overall tree (with a dogwood and some rhododendrons in the foreground). Also attached are a few more photos of some of the sprouts. The second photo shows the trunks of the two large trees that the sprouts are probably coming from. So you’re thinking they are alder trees?Thanks,-Mark WillkeOn Jun 23, 2023, at 12:26 PM, Ask Extension <<personal data hidden>> wrote:

responder: Jacki D., Master Gardener Diagnostician Volunteer (Washington, Multnomah and Clackamas Counties) Oregon State University Extension Service Volunteer Metro Master Gardeners (http://metromastergardeners.org/) Replied July 20, 2023, 2:15 AM EDT
response: These might be elm trees. Please cut a twig and post a clear photo on a simple background. Provide the same with a couple of leaves. See this Oregon Stare Landscape Plants page. There you’ll see twig and leaf photos and that’s the sort that will help me confirm identification.