Questions on: Hackberry

Ron Smith, Horticulturist, NDSU Extension Service


Q: I have 20 to 25 hackberry trees growing on my property. They're 25 to 30 years old and of substantial size. They seem be in good health. However, during the autumn of last year, one of the trees fell over after being hit by a gust of wind. The wood was flakey and easily broken with your hands. Some of the wood turned almost to powder when touched. The tree that fell over had almost white bark in places, while the others don't. The reason I'm so concerned is that some of the trees growing a significant distance from the dead one are showing the same symptoms. I've recently had one snap and deposit a 20 foot "chunk" of tree in my neighbor's yard. I need to know if these observations are symptomatic of a fungus or nutritional deficiency that I can treat or if I need to seriously consider quickly removing all the trees near my structures. (e-mail reference)

A: You need to contact an International Society of Arboretum certified arborist as soon as possible to have the trees inspected before any more collapse. I don't know what the malady is that you are describing, but it sounds like it could be serious. Go to http://www.treesaregood.com/ and then click on "Find a Tree Care Service" to find the nearest arborist. Be sure to check the qualifications and credentials of the individual you intend to hire.


Q: We had a very large hackberry tree cut down because it lost some limbs during an ice storm. The limbs started to break away from the main trunk and the tree split down the middle. It was obvious the tree would not survive. I am trying to split the wood, but it is very difficult. If the hackberry is so tough, why did the large limbs crack off during the ice storm? Do you have any suggestions to make it easier to split, such as letting it dry out? I will try using a wedge to split the wood as soon as the snow goes away. (e-mail reference)
A: Hackberry is very hard wood. If steel plating had not been developed, this wood would be an excellent candidate for consideration! You also probably are dealing with somewhat frozen wood. Why not give the tree company that took down the tree a call? The tree company has powerful chain saws. As to ice breaking the large limbs, the weight is well beyond what almost any limb can withstand. Keep in mind that the aircraft industry is paranoid about the slightest bit of ice formation on the wings or body of the plane because of the heavy weight.

Q: I cut down a hackberry tree and am planning to burn it for firewood in my fireplace. It seems like a very hard wood. Does it burn well? (e-mail reference)

A: It is a very hard wood. If you get it burning, it will yield excellent heat units and not burn up too fast. Enjoy!


Q: I have numerous hackberry trees coming up between my fence and my neighbor's fence. To kill the trees, is there something I can spray on them? They are difficult to get at to cut them down. (e-mail reference)

A: Allow them to leaf out this spring to drain some of their stored energy. After that, spray the trees with a brush or shrub killer available at most garden supply stores or use a legal dose of Roundup.


Q: We have hackberry trees that are not growing. We had the soil tested as you suggested. The pH level is 7.7, the phosphorus is 146 parts per million (ppm), the potassium level is 246 ppm and the sulfur level is 13 pounds per acre. Nutrients in the soil were very low at 5 pounds per acre. We took this sample about 5 inches down. Will this information help you tell us why the hackberry trees are yellow, drying up and not growing? Maybe this area is not meant to grow trees. (McVille, N.D.)

A: The soil test results reveal nothing that should keep the tree from growing normally. I have to think it might have something to do with the planting depth. Since being alerted to this problem by a colleague at the University of Minnesota a couple of years ago, I am amazed at how many trees are planted too deeply. A covering of 3 to 4 inches of soil over the crown will result in the gradual decline of the tree through early leaf drop, leaf discoloration and reduced growth until the tree is killed.


Q: I have a newly constructed home with an existing hackberry tree on the property. To match grade, the tree’s base was covered with 18 inches of black dirt. Will this kill the tree or do I need to dig down and build a small retaining wall around the tree base? (e-mail reference)

A: There is almost a 100 percent guarantee that you will slowly kill the tree over the next three to five years. Dig down to the original grade and out at least to the drip line. That should help save the tree. Someday housing contractors and horticulturists or arborists will get together and communicate that covering tree roots above grade is akin to tying a plastic bag over one’s head.


Q: I have a large hackberry tree with a new lawn under it. This year I have tons of tiny seedlings sprouting under the tree and throughout the lawn (too many to pull out). Is there something that I can use that will get rid of the seedlings, but leave the lawn and trees unharmed? (e-mail reference)

A: Just mow the grass. Woody plant seedlings don’t tolerate mowing. When the seedlings reach the height of the mower blade, the growing tip is cut off and they will die.


Q: We have a hackberry tree that was doing fine until last summer when many leaves turned yellow and fell off. This summer the same thing is happening but far worse. We have heard of a lacebug that can damage these trees. Is this what it is, and if so, what can we do to stop the damage? Can they kill a tree? I have noticed two other hackberry trees in town that have some of the same symptoms. (Ada, Minn.)

A: The lacebug is usually a problem in the eastern part of the country. It affects members of the elm family, which the hackberry is. Hackberry trees are also known to defoliate early for other reasons. Wide fluctuations in moisture are a primary reason. Contact a local Certified International Society of Arboriculture Arborist to come out and diagnose the problem. Since you live in Ada, you might not have one locally, but many will travel some distances for work. Try the yellow pages in Grand Forks if none are listed in Ada, or give Kelly Melquist a call at (701) 729-6899. He’s in Fargo and may be willing to come that far.


Q: We purchased a hackberry tree in a pot from a local nursery. It was a holdover from last year, so it was terribly root-bound. We took the roots and unwound them from the circular pattern they were bunched in and planted the tree according to the directions. The tree remains green if you scratch a branch or the trunk, however it has no buds or leaves. Is this tree a goner? (Jamestown, N.D.)

A: The hackberry is a strange tree. Sometimes the dormant ones need to be “sweated" to get them to bud. So hang in there and see if it will leaf out when our hot weather finally arrives.


Q: I have several hackberry trees growing on my property, which consists of a 100 foot by three mile section of abandoned railroad.The railroad was closed in early the 60s and has quite a variety of good-size trees growing on it. It seems the hackberry trees are beginning to take over on some parts of the property. There are several small saplings coming up. Should I cut them down and replace them with another species of tree? What is hackberry wood used for? (E-mail reference)

A: I don't know why you would want to cut down hackberry trees. To me they are attractive, tough, disease-free (the witch's broom and nipple gall they get are just cosmetic) plants that most people would be happy to have coming up as volunteers on their property. The wood of the hackberry tree is a tough, twisted wood, with excellent resistance to breakage. Good quality wood is used for furniture, millwork and some athletic equipment. Lower grade material is used for crating. Hackberry trees are one of the most eco-friendly trees in North America. The fruits are relished by wildlife because of their raisin/plum flavor. The branching system is such that they are inviting to nesting birds and even those with decay hold up well enough for owls and squirrels to move into. They also attract butterflies with their nectar-rich foliage. The seedlings coming up are from the consumed fruit of visiting birds. Think twice before cutting these trees down. They are good for the ecosystem, as well as perhaps softening what has to be an eyesore, an old, unused railroad track.


Q: I have a golden retriever who loves eating the leaves of my hackberry trees and anyone else's when we go for a walk. She is always on the hunt for them and sniffs them out. Is there something in the hackberry leaf that is medicinal? What attracts her to this particular tree? (E-mail reference)

A: I have never heard of this before. Perhaps she was a horticulturist in another life? Maybe her mother birthed her beneath a hackberry and she associates it with the tender loving care she received as a pup? Watch her the next time to see if she eats just the leaves with the nipple galls on them or the plain ones. There might be something associated with this that only she knows about. Thanks for a good question!


Q: I would like to know if the hackberry tree, its bark or leaves are poisonous to horses? (E-mail reference)

A: It’s not according to my references.


Q: Do all hackberry trees produce the little reddish purple berry fruit? I don't recall the one on our ranch producing them, nor the one in the back of my parents’ yard. The one in my parents’ yard has a 3- to 4-foot trunk like most hackberries. It has corky like veins running throughout the exterior of the bark that covers the whole tree. There does appear to be tiny seeds in the leaves, but nothing like a berry. It is identical to the one on the ranch and I always assumed it was a hackberry. Do you have an opinion? (E-mail reference)

A: Most hackberry trees will produce the seed. The amount depends on the growing conditions. The "seed" you are seeing in the leaves is really a nipple gall, caused by a very small insect called a psyllid. They lay eggs in the emerging leaves and the larval development causes the nipple-like growth to develop around them. Their damage is cosmetic, not lethal. It sounds like you are describing a hackberry.


Q: Hopefully this specimen from a hackberry tree will not be pulverized by the time it arrives in Fargo. This fall after the leaves dropped I noticed some branches with fungus-like growths. They all look brown and dry and are scattered in small clusters on the tips of the limbs. Any information would be appreciated. (Mitchell, S.D.)

A: Your sample of witches’ broom on the hackberry arrived in perfect condition. This is not a fungal disease but an infestation of Eriophyes celtis, a mite that feeds on the tree’s buds. Control is not normally recommended, but if you think it is necessary I suggest spraying with dormant oil next spring, before bud break. A follow-up spray with Sevin insecticide as the leaves are beginning to form is recommended. This is a natural host-mite relationship. Normally the witches’ broom doesn’t get to the point when spraying is necessary.


Q: This is our third summer in a house with a large hackberry tree over part of our deck. This year it has produced a large amount of sap, much more than the last two years. It also has feathery little aphid type insects on it as well as a number of ladybugs that I imagine are eating the aphids. Does this tree have varying sap cycles? Is there anything we can do? Our deck and furniture and a lovely fig tree are turning black and sticky! (E-mail reference, Huntsville, Ala.)

A: I hate to tell you what it is that is dripping on your deck and fig tree, but I must. The "sap" is the "honeydew" from the aphids feeding. It is technically the sap of the tree, but only after it has passed through the gut of the aphid. The ladybugs will take care of them eventually. In the meantime, I suggest an umbrella covering for your fig to keep the fruits more appealing and to prevent a secondary fungus or mold from developing. Next spring you might want to contract with a competent arborist to control these pests. There are systemics available that will not harm the predatory insects like the lady beetles. If you lack the patience for the lady beetles to do their work, you might contact that arborist now to spray the tree with Neem. It is an organic that would take care of the aphids as they feed and not harm the lady beetles.


Q: We have a hackberry tree. It is going on the second season since we planted it. Some of its leaves have little seed-like lesions. Is this a problem? What would you suggest we do with it? (Maddock, N.D.)

A: Nothing. The galls are known as nipple galls, caused by a mite stinging the leaf tissue in early spring as they unfold. It is nothing more than cosmetic damage.


Q: We planted a hackberry three years ago but have yet to see it produce fruit. Is this unusual? The tree trunk diameter is a bit over 1.5 inches. (E-mail reference, Ottawa, Ontario, Canada)

A: I have been asked about apples, cherries, apricots, and plums fruiting but never hackberry fruiting in 16 years of answering horticulture questions. It will bear fruit, most likely, when it is mature enough. That would be about five or six years from now, as a guesstimate. If the tree could have an emotional response, I am sure it would be flattered to have an inquiry about it fruiting, since that is not a major attractive characteristic about it.


Q: Can you tell me what is causing the leaves on my hackberry to curl? The tree is planted near our lake home, and the water was really high this year. (Fargo, N.D.)

A: I suspect a change in the water table is part of the cause, along with a good dose of downy mildew and a touch of leaf-spot fungus. There isn't much you can do if the water table is rising, but you can control the diseases with any number of fungicidal leaf sprays. Cover the foliage after leaf-out, and monitor through the rest of the season. Make additional applications if it appears something is going to get started.


Q: Enclosed you will find some bark from a hackberry tree. The tree seems to be dead, with the bark breaking away. I saw some red beetles on the tree. The beetle kind of looked like a grey potato bug. Can you tell me what is wrong with my tree? (Lisbon, N.D.)

A: Thank you for the good description of the insect you found on the dead tree. Most likely it was the red-headed ash borer, as they are commonly found on ash, oak and hackberry trees at this time of year. There is no registered spray for this insect. The best thing to do is cut the tree down ASAP and get it off the site. I suggest a close monitoring of the remaining trees, and expend any effort needed to keep them healthy. Borers are attracted to stressed, weakened or dying trees. Healthy trees are seldom attacked.


Q: My old hackberry tree has these warts, which don't hurt the tree but damage the leaves. What can I do to get rid of this problem? (Lemmon, S.D.)

A: Your (and everybody else's) hackberry is being infested with Hackberry Nipplegall—a very small insect related to aphids known as a psyllid. They cause no harm to the plants, just superficial disfigurement. If you really want to attempt control, spray with Sevin or diazinon in early spring as leaves unfold, but it is generally not worth the effort


Q: Enclosed are flies that are eating the leaves on my hackberry trees. What can I do to get rid of them? (Barney, N.D.)

A: The flies you included were interesting, but had nothing to do with the leaf damage on your hackberry. They do not have chewing mouth parts.

The damage appears to be that of the larvae (caterpillar) of the empress butterfly—which is now gone. Spraying at this time would be futile, unless their physical presence can be ascertained. Thanks for the good sample.


Q: These hackberry and linden leaves are from trees planted last year. They were translucent, yellow and puckered. (Mohall, N.D.)

A: The samples you sent me showed extensive herbicide damage (likely 2,4-D). They are likely not to survive.


Q: We have more than a dozen 40- to 60-foot tall hackberry trees amongst our timber and three large ones along the river bank behind our home. All apparently
have been attacked by nipplegall aphid larvae. Damage to the dozen or so large trees within the heavily timbered area is so severe that their leaves are very sparse.
Some of these trees almost appear to be dead from a distance due to sparseness of foliage. All of this damage has happened rather suddenly, or at least we first
noticed the problem only recently. Spraying all of these large trees with carbaryl would be a challenge, but I will undertake anything reasonably possible to save all of
these trees, or at least to save the many hackberry saplings. I would appreciate any help or comments you may be able to provide. (Tuscola, Ill., e-mail)

A: Nipplegall would not cause this defoliation. It is more likely a cankerworm or forest tent caterpillar. It could be the insects have already outstripped
their food supply and are dying off, or a predator has moved in to bring them under control. If that doesn't appear to be the case, have the trees
sprayed with Bacillus thuringensis (Bt), a biological bactericide that kills them as they feed and is safe to songbirds and us as well.

Don't worry about the nipplegall. It will always be a part of the hackberry tree.


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