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Hortiscope

Ron Smith answers reader's questions about the world of plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have two silver maples on my property that are 25 to 30 years old. This spring, they both had lots of flower buds and then grew a lot of maple keys at the ends of the branches. All the keys have started to dry and fall off, but there are very few leaves growing. The few branches that did grow leaves look normal and healthy, but the rest are bare. Do you know what may have caused this? I also used a fertilizer on my lawn last fall that had weed control mixed in. The numbers on the bag said 12-3-18. Could this be the reason why the trees look sick? Do you have any suggestions for what I could do to make the trees better? (e-mail reference)

A: The trees are in decline and on the way to dying. I suggest you contact an International Society of Arboriculture certified arborist to see if there is a chance of saving the trees or if removing them would be the better option. Check the arborist’s credentials and be sure the individual or company is bonded and insured.

Q: I have been reading your Hortiscope column on the Web. I am wondering why the bright, colorful leaves on my croton have all turned green. It is flowering and sitting by a north-facing window on the 18th floor. I believe I water it correctly from reading your column. (e-mail reference)

A: The leaves on a croton turn green when there is insufficient light. Get a plant light and direct it on the foliage. It gradually should go back to being the variegated beauty that it was.

Q: I have been trying to find out if I can start lilacs from cuttings in water, sand or potting soil. I can’t seem to find a good source of material. Can you help me? (e-mail reference)

A: Experts are challenged to get lilacs started from cuttings. A tight schedule of specific timings is needed, but even then success is not guaranteed. You are better off to divide a sucker from a parent plant and place it where you want.

Q: My Austrian pine tree was covered with snow, except for the top 3 feet. That top area of the tree did not turn green this spring. Is there anything I can do to get the tree to turn green? (e-mail reference)

A: There is nothing you can do, but it should recover given sufficient time. If it is going to happen, it will do so on its own. You should be getting some candle growth showing on the top of the tree. If that is the case, you have nothing to worry about.

Q: I have a very large silver maple tree that produced a lot of seeds this spring, but produced few leaves. In fact, some branches did not produce any leaves. The other silver maple in my yard looks normal. Any idea what may be happening? (e-mail reference)

A: The tree probably is dying from some sort of root rot or a verticillium wilt type of disease. It would be best to have it removed as soon as possible so it doesn't spread to the other tree.

Q: We have two Nanking cherry trees that have done well. This spring, many leaves are wilting on both trees. There is fruit evident on the healthier-looking branches. We did have unusually cold nights, with wind and plenty of rain this spring. However, we also had some decent periods of warmth. (e-mail reference)

A: The problem could be a canker infection or verticillium wilt. Another possibility is borer or bark beetle activity. Only a close examination of the branches will nail down the problem. If there is a university nearby that has a plant diagnostic lab, I would suggest making contact with the lab to perform a diagnostic test.

Q: A friend has a crab apple tree that has fruit on it from last year. The tree also has no new buds on it. The tree does have leaves. Does it have some kind of disease? (e-mail reference)

A: It is more likely the tree exhausted its resources to set flower buds after last year's record production. As long as it has leafed out and new growth continues, the tree should be OK. Birds apparently had plenty of other choices for food, so they passed up the apple tree.

Q: I’m wondering if you can help me out with a tower poplar problem. We have about 20 of them planted along our backyard fence. The trees give us great shelter and privacy, but a few of them have not produced leaves at the top. Two of the trees look dead. One of the trees has leaves with holes the shape of a C or U. These leaves also have lots of material/liquid/sawdust coming out. Is there anything we can do? Our concern is that we would hate to remove a tree without putting in something else. Should we get rid of all the trees? Would the upright European aspen fit in or would it look strange among the tower poplars? (e-mail reference)

A: Get rid of the poplars. Even if you don't see evidence of anything wrong, the problem is bound to show up on the rest of the trees sooner or later. I would suggest replacing the poplar trees with the upright European aspen. Whatever you do, don't capitulate and plant Lombardy poplars in place of the tower poplars!

Q: Is it possible to transplant mock orange trees? We are doing some renovation work, so the trees need to be moved. The area they will be transplanted to is shady. I would like your advice on how to transplant the trees. (e-mail reference)

A: Get the site where the orange trees are going ready to receive the plants. On a cloudy, cool day or going into the evening hours, dig out the trees with as large a rootball as can be handled. Plant the trees at the same depth. Water them in well. Don't worry about wilting if any takes place. Good luck.

Q: I have two honeycrisp apple trees that were planted four years ago. The trees have healthy foliage and the bark is in fine condition. However, they never have produced any blossoms. The trees get full sun and are on an irrigation system. In addition, I fertilize the tree twice a year. Do you have any idea why they haven't produced any blossoms? (e-mail reference)

A: You are being too nice to the trees! Stop the fertilizing. Do not water the trees unless you go into an extended dry period. Trees pampered this way will delay going to work for you (producing fruit). The trees will be OK if you don’t pamper them as much and might produce some flowers for you along with some fruit next summer!

Q: I have some lilac bushes that are old and don't bloom as much anymore. We never pruned the lilacs, so that could be a problem. We want to cut them down so they will regrow. Will this work and make them bloom a lot again? If so, when is the best time to do it? (e-mail reference)

A: Prune them to the size you want right after the blooms are spent. Prune the lilacs just above a bud or where a leaf comes out.

Q: Help! Is there any way of saving a very large tree that had a major root severed 5 feet from the trunk? The tree is beautiful, so I am devastated that a contractor made this mistake. What can I do? (e-mail reference)

A: If it was just one root, the tree will be OK. Please don't shoot the contractor!

Q: I always look forward to reading your column. You seem to answer questions with a lot of common sense. I have a cotoneaster with a few bagworm webs. I bought some bug killer (Bayer Advanced Mulit-Insect Killer with the active ingredient of Cyfluthrin or Tempo) that I was going to use to kill the worms. In the past few days, orioles have been in the cotoneaster eating the caterpillars and (I think) sipping the nectar. If I spray the webs, I'm assuming that it won't do the birds any good. I enjoy seeing them right outside my window when I'm working on my computer. Do bagworms leave eggs for the following year? Can I cut the branch off with the web on it and dispose of it instead of spraying? I'm sure that the orioles will not take care of every caterpillar. I also have a web in the crotch of a large branch on one of my apple trees. I probably will have to spray that one because I can't cut that large of a branch without damaging the tree. (e-mail reference)

A: Thanks for the nice compliment! Let the orioles do the work for you. Bagworms can be cut off the branches and disposed of as long as you don't disfigure the tree. What you also are seeing is tent caterpillars, which usually are ignored by most birds. I never have seen a flock of birds feasting on any of them, so your Bayer product will be useful. It is a little late for this year, but will be there for next spring's feeding frenzy. No matter how bad the infestation looks and how many leaves the caterpillars remove, the damage is temporary for this year. You will get regrowth after the caterpillars go into the final metamorphic stage. You just don't want them coming back every year because that's when they can weaken a tree.

Q: We have an old Amur maple windbreak. Recently, the power company cut back nearly one-third of the hedge. The company offered to cut the whole hedge down and grind the stumps out. I really love the windbreak and don't want to start over, but I am concerned that the trees have outlived their expected life span, so this may be a good opportunity to remove them. What is the life span of Amur maples? If I prune them back more evenly, will they grow back and fill out more? (e-mail reference)

A: If the Amur maples have lived many years as a windbreak planting and they are relatively healthy, these are tough, well-established plants! They could live another 30 years, so do some pruning to enhance their look. However, any that are sick or in decline should be replaced.

Q: I have a dieffenbachia with very pale leaves. The plant has several stems and some new shoots. I noticed that one of the large stems is slippery and beginning to feel mushy. In addition, some of the lower leaves are yellowing and turning limp. These leaves are not on the stem that is mushy. Other leaves have one or two brown spots per leaf. From what I read, the plant may have stem rot. Is it possible to remove the affected stem and save the remaining parts of the plant? What could the yellowing leaves indicate? (e-mail reference)

A: It sounds like a combination of stem and root rot. If you can find a section of the stem that is not mushy, remove it from the rest of the plant and throw the plant away. Propagate the healthy stem by placing it sideways in a sphagnum peat moss media. However, just barely cover the stem. Keep it damp, but not soggy. In six or eight weeks, new growth should be evident. Plant it in normal potting soil to start a new, healthy plant.

Q: I have a huge hydrangea bush that has not been tended to. It is now so tall that I cannot cut the flowers and there are a lot of dead branches under the green leaves. How much can I cut it next spring? You told someone to cut it back to about 12 inches, but going from a big tree to something that small seems like a drastic change. Please give me some advice. Thank you. (e-mail reference)

A: Cut it now to about to about one-third. Before leafing out takes place next spring, cut it back to the height you want. The advice you were reading is for hydrangea species that bloom on new growth every year, such as the Annabelle.

Q: I have a schefflera amante that has funny, ring-shaped patterns in the leaf. It is not leaf miner and there are no signs of any insects on the plant or in the soil. Do you know what is causing this effect? (e-mail reference)

A: This is a ghost ring virus. I don't know how your plant got it, but usually virus infections are transmitted by piercing-sucking aphids or other nibblers, such as leaf hoppers. There is no cure.

Q: How can I tell if an apple tree is female? Also, can you tell me where to find the seeds that are used for making kolackys? (e-mail reference)

A: There is no such thing as a female apple tree. It must have been a misprint or misinterpretation on your part. I don't know where you can get the seed for the purpose you refer. Sorry!


NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161, ronald.smith@ndsu.edu
Editor:Rich Mattern, (701) 231-6136, richard.mattern@ndsu.edu
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