Questions on: Poplar
Ron Smith, Horticulturist, NDSU Extension Service
Q: I saw your column and am hoping you can shed some light on my poplar tree problem. We have an old poplar tree in our backyard here in Oklahoma. About 40 percent of the branches have leaves on them. The rest of the branches are bare and appear to be dead. The branches with leaves are at the bottom of the tree. One tree service has recommended we cut the tree down. It said poplar trees are prone to disease and insect infestation. Is there any truth to this? Is there a common disease or insect problem that would cause the tree to exhibit these characteristics? (e-mail reference)
A: Your local arborist is right about poplar trees. There is a text devoted to the problems these trees have. Just a few of the problems are borers, bark beetles, stem cankers, fungal leaf spots and vascular disease. Have it cut down and used for firewood.
Q: I have three poplar trees on my property line that are more than 100 years old. I am getting odd trees popping up around my home's foundation. The leaves look like poplar leaves, but five times larger (about the size of a dinner plate). The trees are growing very fast. I didn't remove them when I should have (I just cut the trunk about 3 inches from the ground), so the trees keep growing back. I want to take a saw to the base, but I am concerned that the root system still will grow and the trees will reappear in a few months. How can I get rid of these things before they crack my foundation? (e-mail reference)
A: What you are dealing with are suckers coming from the root system of the old poplars, which very likely are in a state of decline. Poplars tend to develop this type of growth from the roots as they age. Once it begins, is very difficult to manage. I strongly suggest that you contact a qualified arborist to inspect the mature poplars to see if there is something that can be done, such as installing a root barrier, to prevent further spreading. The arborist should do a complete physical on the trees because this species often develops a hollow trunk that would make these trees a hazard in high winds. To locate a certified arborist in your area, go to http://www.treesaregood.com/ and click on "Find A Tree Care Service."
Q: I found your column on the Web and am hoping you can answer a question for me. I have six hybrid poplar trees in my backyard about 25 to 30 feet from my foundation. After eight years, the trees are quite large (more height than width). All of the trees have shallow roots growing in all directions and at least two of these trees have shallow roots that have grown close to my house. I was told that these roots follow the path of least resistance, so the roots will turn when they reach my foundation. Is that true or do I need to be worried? I can see the shallow roots that are spreading, but are there more underground that I can't see? (e-mail reference)
A: You received the correct advice. Roots will develop only in a soil system where there is a balance of air and water. Dry or compacted soil will stop the roots. Think of the root system as a "mining system" where the roots pull moisture and nutrients out of the soil in the presence of air. If the foundation of your house is not broken and leaking water, the roots will not damage it, especially at 25 feet away. There are a lot more roots to these poplars than you see. Other than having problems with the surface roots making mowing difficult, you likely will have more trouble with the branches as the trees continue to mature than the root systems causing foundation problems.
Q: We have a shelterbelt with two rows of spruce and a row with a mixture of acute leaf willow and tower poplars. The towers are suckering a lot, so it is a major undertaking to cut these down every year. The suckers are now spreading to the spruce trees. If we cut these towers down, will the suckering stop or will the roots keep sending up more? (e-mail reference)
A: Poplar tree suckering can become a nightmare. The way I found to conquer this invasion of unwanted sprouts is to wait until the trees completely leaf out this spring and then cut them down. This uses up the food reserves from the roots that were stored last year going into fall. At the point of full leaf-out, the reserves will be at their lowest, resulting in reduced or weakened sprouting. The sprouts that do emerge can be controlled with careful applications of glyphosate (Roundup). If you persist, the battle will be over this summer. Cutting the trees down before they leaf-out allows all the carbohydrate reserves to remain in the roots, which then are available for a strong surge of suckering that will drive you crazy!
Q: My neighbor and I planted 13 hybrid poplar trees in our backyards in 1997. They have grown to about 35 feet and were healthy until last spring. All of the trees bloomed in early spring and had leaves. In May, one of the trees started to drop its leaves. A month later it started to grow new branches with some leaves, but as soon as the drought started, the leaves and branches died. The tree was dead by August. A few weeks ago, I cut down the tree. All the branches shattered when it hit the ground. The remaining 12 trees look good. What happened to the tree? Was it bugs, disease or physical damage from an ice storm last November? (Wahpeton, N.D.)
A: Generally, a broad environmental disaster, such as an ice storm, would have impacted more than one tree. From your description, it sounds like a vascular wilt fungus that killed the tree. If you haven't done so, take the stump and roots out or at least cut a trench between the roots of the dead tree and any adjacent poplars.
Q: We have three large poplars in our yard that are causing problems. The roots are shallow and even growing aboveground. They are difficult to mow around and I'm concerned about people tripping on the roots. What are my options for dealing with the roots? I enjoy your column and have learned a lot. (e-mail reference)
A: You donít have a lot of options. You could build a large bed around the surface roots and plant the area with shallow herbaceous plants. Another option is to cut the trees down. The temptation is to cut out the roots or cover them with topsoil, which many people do. Some get away with it. In many cases, the soil over the roots eventually will lead to a decline in the tree or death. Removing the roots puts the tree at greater risk of toppling during a strong wind. Thanks for the very nice comment about the column!
Q: I had a client bring me a poplar tree sample. The leaves turn brown and leathery before falling off. The infected leaves start to yellow from the outside edge. When you cut open the ball on the leaf, it is full of little bugs in various stages of life. The mature bugs have wings and look like green fruit flies. Any information on what these bugs are and how to control them would be great. (e-mail reference)
A: This is a case of the "barn door" syndrome. There is nothing that can be done at this time. Next spring, prior to leafing out, have the tree spayed with dormant oil. This will kill the emerging insects and their overwintering eggs. Cottonwoods are tough plants once they are established, so the tree probably will come back OK.
Q: I have some Lombardy poplar trees that are dying or dead. Can the trees be used for fire wood? (e-mail reference)
A: Yes, that's about all this tree species is good for.
Q: I want to remove a row of aging poplars and apply Roundup to the stumps to kill the suckers. The trees are close together and have extensive root systems. Will Roundup affect the smaller poplars or other trees in the vicinity? (e-mail reference)
A: Roundup wonít work. You need to purchase a stump killer, which should be available at a garden supply store in your community. Such products are specific to the type of tree stump they are applied to and do not affect adjacent trees.
Q: I thought Iíd ask another question because you did so well answering my last question. I have a young aspen that is giving me trouble. There are three trunks in very close proximity (all one tree?). Oddly, one has very yellow-green leaves while the other two have dark green leaves. I assumed that this was due to chlorosis and added some liquid iron (planning to get the soil tested this spring before doing any further amending). Later in the year, the tree appeared to exhibit signs of shoot blight. Iím guessing that the decreased vigor of the plant and our cool, wet summer had something to do with it. It may have been infected last year, but I didnít notice because we bought the house in June. Could you offer any suggestions as to an appropriate course of action? (e-mail reference)
A: Take out the problem tree trunk. If you donít, it only will go downhill from here. The root system is damaged or diseased and will not improve. I speak from experience in attempting to correct maladies as you describe. I have tried iron injections, aeration, vertical mulching, etc., but to no avail.
Q: We have three poplars in our backyard that are probably over three stories tall. The last two summers we have noticed a decline in the number of leaves. This summer we only have some leaves on the lower branches. We are assuming the trees are dead. A few of our neighbors are also having the same problem. How do we get rid of them if they are dead? Is there a company that will take out the trees? If there is, how much should we expect to pay? (Fargo, N.D.)
A: Unfortunately, poplars dying in our area are very common. There is a competent, honest, qualified individual who has done work for me and others that I can have you contact. His name is James Danielson, owner of Cougar Tree Care. His phone number is (701) 729-7208. The cost of removing the trees depends on where the trees are located, how many hazards are in the way and their size. It would be a good idea to get them removed at your earliest convenience because they may have heart rot, which could result in the tree falling on your house, car or even you on windy days.
Q: About three weeks ago I planted 10 tower poplars in my back yard. I chose this tree because I read they are fast growing and make good privacy screens. Our back yard is right off a busy street. However, after reading some of your columns, I'm having second thoughts and wondering if I made a mistake. In addition, at least one of them appears to be dying and four others seem to be heading in the same direction. The leaves are turning brown and falling off. I'm so disappointed, but I don't know what to do. Should we take them all out and replace them with better trees or can we save them? Should we replace the sick ones? (e-mail reference)
A: At least you didn't plant the Lombardy poplar, which is the worst of them all! The tower poplar is a hybrid and is considered an improvement over the Lombardy because the disease pressure isn't as great. It does sucker, which can drive people crazy. I have seen healthy tower poplars that look terrific, but many succumb to leaf spot and canker diseases. You have to accept that, if you plant a poplar species, you are very likely to have some disease or insect problems at some point. I would suggest removing the trees that have problems and replacing them with populus tremula erecta. Its common name is upright European aspen. Of all the poplars, it has the best resistance to disease and insect problems.
Q: I have a poplar tree that is approximately 20-years-old. From previous experience, I have found that they rot from the inside. Can you tell me how to check if it is rotted without cutting it down? Some of the bark looks like it is no longer snug against the tree. (e-mail reference)
A: One way to find out if a tree is hollow is to thump it with a rubber mallet. Another method is to use an increment borer which drills into the tree, taking out a core. This will tell you if the tree is hollow, solid or solid but rotting. A regular drill with a small bit would work too. As you go into the tree, if the center is hollow or rotten, you'll feel a change in resistance to the drill. Just remember to use a small bit. Trees can recover from small wounds pretty quickly. (JZ)
Q: We have a Lombardy poplar right at the property line. The trunk is 2.5 feet in diameter and about 50 feet high. We obviously know this tree will be trouble, because there is a block property wall within two feet, a backyard sprinkler system, a house foundation (slab) within 30 feet and we have neighbors concerned about their children's safety. We are going to have the tree removed by a local tree trimming service, but I want to prevent any future root or sucker problems. I understand that after taking down the tree, we should treat the stump and roots. Should we treat the stump or have it removed? You have recommended using RoundUp, but we have dogs and are concerned about their health. I have heard of treating stumps with rock salt. If this is the case, how much of the stump should remain, how should we prepare the stump and how should we apply the rock salt or other sucker-stopper herbicide that will translocate into the vascular system? (E-mail reference)
A: Have the tree and stump removed. As the suckers come up from the roots, spray them with a weed killer called TRIMEC. It translocates quickly and will be effective in killing the roots. Keep your dogs away from the sprouts for 24 hours after an application.
Q: I want to plant some poplar trees where spruce grew for 30 years. There is a thick bed of pine needles in the area. Someone told me nothing will grow in that area. Also, I want to transplant asparagus. Does transplanting require any special care or consideration? (E-mail reference)
A: The spruce needles make excellent mulch. While in place, very little will emerge from the nice thick mat that has developed over the years. If you pull the mat of needles back and plant into the rich soil below, I'm sure the poplar trees will establish themselves and grow if given proper care. Move the asparagus as soon as reasonably possible. Set the crowns about six inches below the surrounding soil, with ample compost, peat moss or rotted manure. Be sure it is planted in a full-sun location.
Q: You suggested we remove our Lombardy poplar trees in order to rid the yard of new trees that pop up, sometimes yards away from the mother tree. We took your advice and cut down nine huge trees. The company that cut down the trees removed the stumps and applied some type of chemical to supposedly kill all the roots and trailers. Do you believe removing the trees and using chemicals will take care of the problem or will we have to tear up our yard in order to get rid of new growth? I'm having a hard time believing that new trailers don't already have a good start and will keep growing on their own. Any suggestion on new trees to plant in their place? We are looking for some fast growing trees. (E-mail reference)
A: You are right to be a skeptic but, don't despair. Treat the suckers that will be coming up with a broadleaf weed killer. Trimec, applied two or three times this season, should take care of the problem. If you want the same tree form as the Lombardy, you might try the upright European Aspen. It has fewer disease problems and grows rapidly. Botanically, it is known as populus tremula 'Erecta'. It is a native of Sweden.
Q: I removed two Lombardy poplar trees this fall and I wonder what you would recommend for replacement? Which is the better evergreen, the Blackhills spruce or the Ponderosa pine? (Garrison, N.D.)
A: Try to locate either the upright European Aspen or the tower poplar as a substitute. As far as the evergreens, you can't go wrong with either. Both are native to North Dakota.
Q: This spring I planted a row of seven poplar trees, a row of 35 Lilacs, a row of 15 sumac and a grouping of three red maples. All of the plants came from our county Soil Conservation Service. I've made about 20-24 inch diameter rings to hold mulch out of thick plastic edging for each tree or bush. They all seem to be doing very well. Iím almost finished putting plastic and rock on top of each row to prevent any grass or weed growth in between the trees. I mulched heavily inside each ring with cypress mulch and water thoroughly once a week if we don't get rain. The trees and the landscaping all look great but are there any problems that the plastic and rock could cause? Is there anything else I should do to keep them healthy? (Lisbon, N.D.)
A: It sounds to me like youíve given the project a lot of thought and done a lot of work to get these plants established. If you haven't overdone the mulch around the plants (greater than four inches), they should be ok. It certainly will not be your fault if they don't turn out beautifully!
Q: We have a row of Lombardy poplars. Our former vengeful neighbors planted another row of poplars parallel to ours on their property. The new poplars did not do well so the new neighbors pulled them out. Now suckers and roots are growing from the pulled out trees. The new neighbors claim the suckers and roots are coming from our trees. What do you think? (E-mail reference)
A: You both have self-inflicted headaches. The Lombardy poplar ranks among the worst trees to grow for landscape purposes. The root suckers are coming from both of the plantings and will continue to do so for years to come. You would be better off pulling yours out and both of you getting the stumps and roots ground out and then smoking a peace-pipe. There are much nicer trees that can define a property line in a non-offensive manner.
Q: What are the options for a large poplar tree that is sending out suckers up against the foundation of a house? Can they be sprayed with a contact like Roundup without causing too much damage to the tree itself? (Hettinger, N.D.)
A: Apply Sucker-Stopper, a commercially available product in garden centers. Also, a product known as Biobarrier may need to be installed to keep the root system in check. Roundup is a bad option because it is absorbed into the tree's vascular system which could cause problems beyond killing the suckers.
Q: I have a question regarding a poplar tree on the edge of my property. It is about 20 feet tall and about two feet in diameter and it seems like the only branches are high on the tree. It is a light color and it had a good amount of foliage this year. Does it weaken the tree if there was a recent disturbance to the ground on one side of it? Is the tree diseased if there is foliage mainly on the upper portion of the tree? (E-mail reference)
A: Soil disturbances over any part of the tree's root system will have an impact on the tree, immediately or down the road, depending on what kind of disturbance takes place. I cannot diagnose the tree's problem from what you have told me. If it is important to you, I suggest making contact with a certified arborist in your community to analyze the situation.
Q: I was recently in Punta del Este, Uruguay, and noticed a beautiful tree with a delightful silver tone to the underside of the leaves. My friend in Uruguay told me this tree is called Alamo Plateado in Spanish. As best I can discern, this translates to Silver Poplar. Am I correct? (E-mail reference)
A: If you are correct in identifying this tree as silver poplar - Populus alba - then it is a tree that you don't want on your property. It is a very tough tree that can take anything that gets thrown at it short of a direct hit from a bomb. The root system would be a major problem. They are invasive and suckering. Its asset is that it can survive just about anything!
Q: I have a question about an oily film that has been covering the trees in our area. I have 36 acres of poplar forest and it is covered! This sticky oil is all over trees, shrubs, vehicles, etc. Some tree leaves (eg. saskatoons) have been turning black where the sticky oil is. Do you have any idea what causes this? (E-mail reference)
A: The oily film you are making reference to is very likely honeydew from aphid infestations, which seems quite common this year, especially on poplars. You might do some close examination and find the trees literally crawling with ants. This is a good indication that the aphids are up there, as the ants "farm" the aphids for maximum honeydew production, which the ants harvest as a food source for themselves. The blackness is a sooty mold that is a secondary fungus from the honeydew, and if it is intense enough, can result in the indirect death of the plants due to a cut-off of light to carry on photosynthesis. I think spraying is impractical on 36 acres of trees at this time. You might consider dormant oil spraying next spring before new growth begins, which will take care of most of the overwintering individuals and be less toxic and less expensive than conventional spraying.
Q: We recently moved into a house built in 1997, so the trees have been there for maybe four years. The previous owner put in four poplar trees. There are also two lindens and two crab apple trees. A bit overdone. We have underground sprinklers so I am nervous about getting the poplars out of there. What is the best way to do this? (He also had two weeping willows, but I got those out as soon as the snow melted.) Also my lindens are looking sickly, with very small leaves. I am watering and putting on aluminum sulfate to counteract the clay soil. What else can I do to help bring them back? (Fargo, N.D.)
A: I suggest doing to the poplar trees exactly what you did to the weeping willows--cut them down and grind out the stumps. The lindens could be affected by the lawn sprinkler system, most likely getting too much water. They are very adaptable trees and don't need any special soil treatment. When were the trees planted? Are they planted too deep? That seems to be one of the most common causes of loss with these trees, along with overwatering.
A: Be thankful that the problem showed up only after four years, because then you can be motivated to replace it with something more worthwhile than a poplar tree. I have an entire book dedicated to diseases of poplar trees. The one in your yard must be a requirement that the housing contractor had to install to consider the job complete. I strongly suggest that you get the tree out of there and visit a local nursery or garden center to get a replacement. There are lindens, birches, Japanese maples, silver maples, sugar maples, Norway maples and even DED resistant elms that would be a better choice, plus a lot more. Poplars would only plague you with surface roots, invasive roots, breaking branches, and a whole book full of diseases and would not add value to your property as it matured, if it lived long enough to do so!
A: As for poplars and their problems, take your pick! There is an entire book dedicated to poplar trees and their problems. Stem cankers, leaf spot fungi, root rots, etc. Probably the only way to determine what is happening is to have our diagnostic lab to do some tissue sampling. Otherwise, just write them off as a loss.
A: It doesn't sound too good to have a poplar not in leaf at this time of year. I suspect it could be the roots have caved in, or the buds were killed off by the winter. If you don't have any foliage emergence turn it into firewood.
A: The poplars are noted for their problems, mostly branch cankers. Once the canker has set in, little can be done about it except to prune out the affected branches at least 6 inches beyond the visible canker area. Depending on the canker development, stimulating growth may help to control spread by compartmentalization from the vigorous growth. Unfortunately, no sprays have proven effective.
A: Poplars are noted for their weak wood and possible limb fall. It is a good idea to get a qualified arborist out on a regular basis to have the tree inspected and pruned to get the deadwood out, at the very least, and remove any limbs that may be potential problems later in the season.
A: If you can, convert the area that is "rooty" in your lawn area to a flower bed. If this is too extensive, you can cover the roots with a couple of inches of topsoil, but the roots will simply migrate to the surface again in a few years. If you don't like the trees, take them out. Life is too short to suffer because of obnoxious roots. You can plant many other trees that will not give you such a problem.
A: The silver poplar -- Populus alba -- is a tough tree that withstands most stresses in the environment, including but not limited to having the roots covered with blacktop or concrete for a parking lot, compaction from continuous vehicle traffic, salt spray from snow covered streets, and more. Killing it will not be easy. You want to get a systemic herbicide that will translocate through the vascular system. As extensive as the roots are on this species, you will have to likely fight it for a couple of years. Spray the foliage that comes up with a product that contains glyphosate (Roundup in the U.S.). Allow the sucker to sprout to a couple of feet in height if you can, then spray it completely. The material will kill any green vegetation it touches. Material that simply burns the foliage back is not effective in getting complete control and will only frustrate you. Whatever you have available in New Zealand that translocates once applied is what you want to use. Just hang in there and persist - you will eventually win, I promise!
Q: I had three big Poplar trees cut down and the stumps ground last fall. Now I have little suckers coming up all over my yard. What would be the best way to get rid of them so they don't come back again? (e-mail)
A: This is a common affliction with poplars--also with chokecherries and plums. I apply a broadleaf herbicide like Trimec. This translocates to the roots which eventually kills them off. It will probably take a couple of years to get them all killed off, but there is really no other way. Make the application a day before mowing so that you have good surface area for absorption.
Q: I have a poplar tree that always has weeds under it. To eliminate the weeds, I sprayed Pramitol. I was careful to stay at least 10 feet from the base of the tree, but apparently the tree still absorbed some because it defoliated and releafed three times throughout the summer. Do you have any ideas what I can expect next summer? Will it kill the tree, or will it just continue this pattern? (e-mail)
A: What you applied was a soil sterilant over a shallow-rooted tree species. The tree's reaction was the result of some of the material being taken up. What will happen this spring is anybody's guess. My advice is simply to wait and see. Thanks for making e-mail contact.
Q: Can you please tell me what these knobs are that are growing on our Northwest poplar, and what we can do to stop the spread of it? (Garrison, N.D.)
A: Your poplar has a stem gall which is caused by various creatures: aphids, mites, midges, flies etc. The damage is local, and other than premature leaf drop or stem breakage on affected branches is usually not a problem to the survival of the tree.
In your particular case, the gall is caused by the feeding activities of an as-yet-undescribed species of eviophyid mite. If you can, prune out affected branches prior to leaf-out next spring.
Q: I have some poplar trees with bugs on them. I have enclosed a sample, and if you open the ball they are full. What can be done? (Steele, N.D.)
A: The poplars have what is known as leaf petiole gall, most likely formed by small gall wasps that lay eggs at that point.
When the young hatch, their feeding activity causes this gall (or cell proliferation) to take place.
No harm and nothing to do. Just enjoy another wonder of nature.
Q: There is a canker or a gall on one of our "tower" poplar trees. It is
about 4 feet up on the main trunk of the tree, looks like a big wart. It goes about half
around the tree and is dark brown, blackish and very hard.
Should we try to cut it out or should we spray it with something? Would appreciate whatever information you have. (Pettibone, N.D.)
A: What I think you are describing is known as a "conk." These conks or fruiting bodies of Basidiomycetes, are indicators of advanced decay, resulting
in your tree becoming increasingly structurally weakened.
This requires a judgment call on your part and you are better to err on the side of plant removal than keeping it around too long where it could cause
damage to property or person. Cutting the gall or conk out will not solve the problem, as the area around the growth is loaded with spores. From your
description, I would suggest removal of the tree and replanting with something else that is healthy.
Q: We have a yellow poplar tree that is about 3 feet in diameter. I'm not sure how old
it would be, but it has always been quite full, until this spring. Now half the tree
is dead and on the other half the leaves are extremely small and the flowers are not filled out. We can't find any insects on the tree nor any sign of disease. What
could have caused this? What should we do to revive this tree? (Dayton, Ohio, e-mail)
A: If the one side of the tree is really dead (no green cambium showing beneath the bark) then there is nothing that can be done. If there is some life
there, then get an arborist to come in and fertilize the tree. Try to encourage new growth. But frankly, I'm sorry to say, there probably isn't much hope
to save it.
I would also encourage you to have the tree checked for internal soundness, as I'm afraid that trees that large will often have a decaying center, causing
the tree to be a physical hazzard to both property and body.
Q: We have a yellow poplar tree which is about 3 feet in diameter, so I'm not sure how
old it would be. It has always been quite full until this year. Now half the tree
is dead and on the other half the leaves are extremely small and the flowers are not filled out. We can't find any insects on the tree nor sign of disease. What could
have caused this? What should we do to revive this tree? (e-mail)
A: The problem sounds like a disease of the vascular system or root rot. There is a disease known as Verticillium wilt that takes out poplar trees. The
disease is soil borne and is very opportunistic. But that is only one of many. At any rate, the future of your tree is not good, and I suggest that you make
arrangements to have it removed at your earliest to prevent property or personal damage. Trees that age often have internal decay that is not obvious
from simple observation. Allowing a dead tree to languish on the property is simply asking for a disaster to happen. Don't allow yourself to be caught
up in one!
Q: I have a beautiful silver poplar in our yard. Last fall, there started to be knobs popping up in the yard. I am trying to chop them out and replant grass. Please let me know of any suggestions on what to do about this. (E-mail reference, S.D.)
A: I am afraid that you have a tree that is prone to producing those "root knees" in lawns. The silver or white poplar (Populus alba) is one of nature's toughest trees, able to grow under some of the most impossible conditions I have ever seen. But, along with that toughness come some characteristics that cause it to lose favor with the owners, and those surface roots are one of them.
So, other than chopping them out like you have, I cannot make any other suggestions for you.
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