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Hortiscope

Ron Smith answers reader's questions about the world of plants and gardening.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: We have a well with concrete sectional culverts. The well is vein fed, but I check it when we have abnormal rainfall to see if the water level is higher than normal. Recently, I was surprised to see what appear to be tree roots growing through a joint in the curbing about 16 feet below ground level. There are two trees close to the well. If I cannot determine which tree is the culprit, I am afraid they will both have to go. (Valley City, N.D.)

A: There is no way I can determine which tree is causing the problem, but you could hire a contractor to cut the root out of the well and repair the open joint. While everything is dug up, a root barrier could be installed to keep this from happening again. This won't be cheap, but neither will the removal of the trees. At least you'd be able to keep your trees.

Q: I saw your answer about what to do to discourage rabbits from eating flowers in the garden. I do a light sprinkling of blood meal around the garden and don't have rabbit problems. After a rain, I reapply. (Moorhead, Minn.)

A: Thanks for relating your success with blood meal! I personally have not had the same success. My wife and I use Plantskydd, Liquid Fence and chicken wire barriers. Thanks for being a faithful reader!

Q: I have two apple trees that were here when I moved in. One has spots on the leaves that I did not see before. These spots occurred as it was leafing out this spring. How can it be treated and with what? (Moorhead, Minn.)

A: Your apple tree has the typical symptoms of cedar-apple rust. It cannot be controlled this growing season. Next spring, spray the tree with lime-sulfur while the tree is dormant. Spray again as the flower buds are starting to swell and turn pink. Repeat as the flower petals begin dropping and again 10 days later. Use a fungicide that is labeled for controlling this disease.

Q: You mentioned in your Hortiscope column not to use landscape cloth and rocks. Is the problem with the cloth, rocks or both? I would like to use landscape cloth that allows water and nutrients to flow through and cover it with wood chips. I get millions of tiny trees growing in my flower beds every spring and I thought this would curtail their sprouting to eliminate so much weeding. Old age and arthritis are creeping up on me and I am finding it harder every year to weed my flower beds. I appreciate your column because it's very informative. (e-mail reference)

A: In my opinion, both. I can empathize with the aging process because I don't bend as easily as I used to, either! What you can do, unless you have a strong aversion to any chemicals, is to get everything cultivated and then apply Treflan. Water it in. This will form a very good chemical barrier in the soil and kill the weed seeds as they germinate. Cloth with wood chips over it will have seedlings coming up, but the seedlings will be much easier to remove. Avoid stone or you will realize just how bad your arthritis really is!

Q: I have a plum tree that is setting fruit for the first time. It is growing very well. However, it has gotten to the point that it looks unkempt with all the new growth near the top. Would it harm my tree if I trimmed the new growth at this time of the year? (e-mail reference)

A: Pruning at this time of year, especially the succulent new growth, increases the chance for pathogens to get established in the wound created by the pruning cut. It won't physically hurt the tree to do it now, but it is better to prune before the buds open in early spring.

Q: We have a silver maple that is weeping a sticky, white substance from its leaves. We have never seen the tree do this before. There is so much of the sticky substance that, if you shake a branch, it rains. The substance has covered the deck, patio, roof, windows, plants and everything else in its reach. It is very difficult to remove. Upon inspection, the other maples in the yard also are doing this. What is happening and what can we do to control this mess? (e-mail reference)

A: What is raining down on you and the surrounding area is insect poop! It is coming from aphids, cottony cushion scale, spider mites or any other insect species that find your silver maples a tasty treat! Rather than spray these large trees, I suggest getting an International Society of Arboriculture certified arborist to inspect what pest is doing this voracious feeding. The arborist will apply some systemic insecticide to the base of the trees or inject the trees with something that will translocate through the vascular system and kill whatever is feeding on the trees.

Q: We have three or four American arborvitae trees along the back of our house. They were there when we moved in seven years ago. We are putting a deck on the back of our house and need to remove these trees. Can they be pulled out? Is it better to cut them down and then have the stumps removed? The trees are about 2 feet from our house, so we're worried that we will mess up the foundation by pulling the trees out. (e-mail reference)

A: Get a competent, licensed or certified arborist to do the job. Be sure the arborist has insurance and credentials. Pulling out the stumps will not damage the foundation. It has been done successfully many times.

Q: Could you please tell me why my lilies would be turning yellow on the bottom? The day and Asian lilies are doing fine, but the others are not and I don't know why. Any help would be appreciated. (e-mail reference)

A: Foliar discoloration, such as you describe, is usually caused by too much water or the crown and roots are beginning to rot. Do not overwater the plants. If you are not overwatering, dig up the ones that are showing the discoloration and examine the roots and crown for borers, rot or anything else that could be causing the problem. If the damage is extensive, discard the whole plant. If the problem is confined to a small part of the plant, cut it out, treat with sulfur dust and replant.

Q: My husband and I have a new home and planted some columnar poplars. I'm not certain what type they are, but they aren't Lombardy poplars. We wanted fast growth in order to cut down the wind and provide privacy. The trees seemed to grow quickly and evenly the first year. Most of the trees continued to do great the second year, except for two at the end of the row. They appeared to be alive, but that was all. This year it was the same thing. I called the nursery and they suggested fertilizing with Miracle-Gro every week until the middle of July. I treated all the trees when I saw burnt leaves last spring and this year. After I did some research on the Web, I guessed it may be a fungus. I used a three-in-one spray that you can get in any department store. They regained new leaves, but the two problem trees only are surviving, not thriving. There were a lot of weeds, so I sprayed the area with a broadleaf herbicide. Today I went out to apply the weekly fertilizer and was dismayed to find knifelike slits on the main trunks of the two bad trees. There was some leaf loss that was not apparent a week ago. Should I give the two trees the last rites or is there one last thing I can do? If I replace them with another variety, will they look enough alike so it isn't so obvious? (Hettinger, N.D.)

A: You have to be one of the top contenders for the "Patience of Job" award! Give your trees their last rites and replace them from the same nursery. The size difference will be apparent at first, but gradually will disappear with each passing year. I have no idea what caused the problems you describe. Let's hope it doesn't come back with the replanting!

Q: I have a question about webworms. I have sprayed numerous times since they started falling from the tree. However, they keep migrating to the front door and windows. Are the webworms searching for cooler surroundings? How long does it take for the chemical to kill them? I used Malathion, which was recommended to me. The webworms are falling by the thousands from the tree, but they don't seem to be dying. Is this just an extremely bad year? (e-mail reference)

A: A "bad year" depends on where you live. In eastern North Dakota, the webworms have not been any worse than usual. While the insecticide you mention is an effective control, you might consider using Bayer Advanced Tree and Shrub Insecticide (Merit). It is available at most garden supply stores. Follow label directions and you will get 12 months of protection.

Q: We have two purple mountain ash trees that are fertilized every year. The trees have grown quite well. The one in the backyard has a beautiful pyramidal shape and the leaves turn purplish in the fall. The last two summers, we constantly find twigs on the lawn. The twigs are dried up and brown, but the tree looks healthy. The tree in the front yard has leaves that turn yellow in the fall. It does not drop leaves, but has distinct weeping branches that always need trimming so we can walk under it to mow. I have noticed many dead branches in this tree when you look straight up the trunk. However, if you stand back, it looks healthy. Do I need to worry about either tree? I don't want to lose them. (Indiana)

A: It sounds like you ended up with two different cultivars of the same species. While some twig and branch dieback is normal in all tree species, mountain ash trees tend to have a problem with cankers and borers as they get older. I would suggest contacting a certified arborist to examine the tree to see if there is anything that requires serious attention. I would suggest that you treat this the same as an annual trip to the dentist for teeth cleaning. It is better to make regular, small investments in tree care, especially when the trees start having a value impact on your property, than to try and rescue them from a hopeless situation. Be sure to check the arborist's credentials and ask for references before allowing any major work to be done.

Q: I planted five techny arborvitaes last September. The middle plant started wilting and losing color late this spring. At first, the nursery suspected watering problems, so I changed that. However, I thought it was a bit weird that just the middle plant was being improperly watered. Despite the adjustment, the tree died. The rest still are doing fine, but have a few small (as in a leaf or two here and there) brown spots scattered throughout each plant. Is that normal? Should I do anything? I really don't want to lose more plants if I can help it. (e-mail reference)

A: Do you have hair that occasionally falls out of your head? The answer is yes. An occasional leaf falling off is normal on these plants as well. I have no way of knowing what killed the plant, but I suspect that it was some type of root rot. I would encourage a monthly treatment of Miracle-Gro fertilizer. Do that until the first week in August, then stop to allow the plants to harden off going into winter.

Q: I have a lagoon-type pool. I want to cover my neighbor's garage roof near the pool, but I have very limited space between the pool and fence. I'm considering a weeping willow because it will enhance the pool. I heard that weeping willows have advanced root systems. Can this damage my pool or disturb my neighbor's property? If so, can you suggest an alternative tree? (e-mail reference)

A: A willow tree would be appropriate. If your pool has a solid foundation that doesn't leak, you should have nothing to worry about. If it leaks, then any tree is going to be a problem. Willows have very extensive root systems that go well beyond the canopy spread of the tree. If the willow dies or is cut down, there would be a small forest of volunteers popping up everywhere.

Q: My husband has two cactus plants that he received from his great-grandfather. They are very old, but appear to be in good health. I repotted them about a year ago and feed and water them once a month (per the food directions). They grow new sections at the top (sort of look like rabbit ears), but the new growth cannot stand on its own. I have to hold it up by tying each piece to a pole with string. Is this normal? The plants mean so much to my husband, so I want to make sure they are around for a long time. Sorry, but I do not know what type of cactus we have. (e-mail reference)

A: What you are going through with old, indoor cactus plants is normal. I suggest taking and propagating the new growth. That way the plant is not so top-heavy. This is something that almost anyone can do and you can share the offspring with family and friends.


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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