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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: My husband started two pink lady apple trees from seed. He just noticed that the trees have a white, powdery substance on the leaves. Any suggestions on what this might be and how to treat the problem? (e-mail reference)

A: The problem is powdery mildew, which is a low-grade fungal disease brought on by high humidity, not enough direct sunlight, and poor air circulation. It generally is not lethal to the tree when mature, but at the young stage these seedlings are at, they could be set back severely. To stop it from spreading to new growth, get a fungicide, such as Funginex, to protect the plant. It is very important that the seedlings are sprayed next spring while they are dormant because reinfection comes from the stems and buds.

Q: I recently moved into an older house that has some grapevines along the side. This is our first house, so I don't have much gardening experience and none as far as grapes go. I am not sure what variety of grapes these are. The vines have purple fruit and large leaves. Could you give me some tips or maybe direct me to some good literature? (e-mail reference)

A: Old grapevines are as tough as nails, and will take over the yard if they are not contained. It is difficult to verbalize without demonstrating what needs or should be done to maximize fruit production every year. I know of a Web site that you can refer to. It contains much more information than you need, but it should answer your questions about how to manage a mature grapevine. The information is available at

Q: We planted a Tuscarora crepe myrtle as a landscape tree in the front of our house. The first summer it bloomed profusely. This spring we experienced a bad freeze that lasted for several days after this tree had developed buds. All of the buds died and the tree did not appear to be alive. We eventually pruned off the top branches. Since then, there have been many suckers that have grown from the base and even a few new branches on the remaining trunk. When and how can we prune this bush to become a tree again? (Somerset, Ky.)

A: Prune it next spring while the plant is dormant. For now, allow as much foliage to remain on the plant as possible because it is building carbohydrates for new growth next year.

Q: We have several Chinese elms that are nice and provide us with lots of shade. However, what do you recommend using to kill all the new Chinese tree suckers that are taking over the lawn? (e-mail reference)

A: Treat them like the weeds with applications of a broadleaf weed killer on your lawn. Lawn service companies would be able to keep them in check.

Q: I have a question about my garden. I have a substantial garden and everything is blooming. However, I have noticed that there are no bees around to pollinate the plants. Is there a spray or dust that can be used to pollinate the plants? My patch is too large to pollinate by hand. Are there any other insects or bugs that might pollinate the plants? (e-mail reference)

A: Look for a product called blossom set. It encourages fruit set and development. In the future, plant some herbs, such as borage and anise hyssop, in and around your vegetable plants. If there are bees in the county, they will be attracted to these plants and also will pollinate your vegetables!

Q: I just bought a hibiscus plant that I want to leave it outside for winter. Is there anything special I should do for this plant before then? I live in Virginia, so we don't get too many snowy days. (e-mail reference)

A: If your neighborhood has hibiscus surviving outdoors through the winter, then you have nothing to worry about. Snowy days are usually not the killer of plants like these. The killer is extremely low temperatures. I would talk to someone locally to see what that person does to get the plants to survive the Virginia winters.

Q: I have 10 arborvitaes on my property. I would like to pull them out and move them to another location. What time of the year would be best to do this, and what is the best way to go about it? (Long Island, N.Y.)

A: In your part of the world, fall would be best, but wait until after a frost or two. Move the plants with as much of the original soil ball as possible and replant at the same depth.

Q: I live in Iowa, so the wind can be brutal. I keep thinking of purchasing arborvitae (large conifers and blue spruce get expensive). I see all sorts of varieties and prices on the Internet. I expect to spend around 20 dollars or so per tree with a height of maybe 3 feet. A local store is selling 7-foot trees (late season now) for 25 dollars. I want to get a quality plant and am hoping you can provide some suggestions. (e-mail reference)

A: I would not purchase trees on the Web. The local retailer has some at a good price and, at this time of year after sitting in their lots all summer, they have to be as tough as crowbars! Not necessarily so with something purchased on the Web. Be fussy about what you pick locally, which is something you cannot do when purchasing online.

Q: You were so helpful some years ago when I had raspberry questions. I have little, green, iridescent beetle bugs. What can I use on my apple trees and other plants to stop them? Is there a spray or something? (e-mail reference)

A: Glad to help. It sounds like the pests could be Japanese beetles. The beetles are voracious eaters of leaves, especially anything in the rose family! You can use Sevin because it has little residue, but you must catch them when they are relatively inactive, such as early morning or evening.

Q: My lilac bush is beginning to drop its leaves. The leaves at the top are starting to turn yellow and falling off. I recently planted some lilies around the lilac bush and also mulched it. Could this have an effect on the plant? (e-mail reference)

A: Check the plant for cankers or lilac/ash borer damage. The plantings and mulch should not be causing this problem unless it was overdone.

Q: I live in Benson County. This morning I noticed my flowering crab has yellowing leaves with dark spots on them. The tree also is dropping leaves. How do I treat this? (e-mail reference)

A: This sounds like apple scab. For now, pick up all fallen leaves and spray the tree with a fungicide, such as Funginex, to keep it from spreading. Next spring, spray the tree with lime sulfur before it leafs out, and spray the Funginex or Bordeaux mixture when the tree is in full flower, but the bees are not active. Repeat the application in 10 to15 days.

Q: I have an ash tree in my front yard that appears to be having some health issues (see attached pictures). I am going to guess the tree is close to 30 years old. The leaves did not return on about half of the branches this spring. I don't see any signs of the bark peeling off. I am wondering what I should be doing to help the tree. Do I need to trim back some of the dead branches or spray it with some type of chemical? If so, what is the best time to do something? I realize that this is a few months late, but have been gone on business travel and didn't realize the severity of the problem. The tree is not completely dead and I would like to save it. (West Fargo, N.D.)

A: I see this is a boulevard tree, so I think it is the responsibility of the city to remove and replace it. I would check with the Forestry Department to see what its policy is. It appears the tree is beyond saving. It may have succumbed to a disease of some sort, such as ash yellows, from just a symptomatic observation. It would have to be confirmed with a lab test to be sure.

Q: I have two small wiegela bushes I planted two years ago. I'm not sure which type they are, but they get a little purple/pink flower on them. The first year they were very small, but did get some flowers. I read that they should be pruned way back in late fall, so that is what I did. This year, they came back, but only the leaves grew. Do you think they will bloom this year? If not, can you tell me why? (e-mail reference)

A: Wiegela bloom on new growth, so it should have flowered or be in flower by now, depending on where you live. These plants are fussy about soil fertility and drainage. If it is poor, the flowering will be poor or nonexistent. If good, the blooming will be prolific. I would encourage you to move it to a sunny spot in your yard. Do all you can to provide good, basic soil fertility and drainage to see if it helps the bushes bloom.

Q: What is the best time of day to mow a lawn during the hot days of July and August? (e-mail reference)

A: For the least amount of stress on the lawn, the evening hours are best. Mowing is stressful to the plant, so mowing in the early morning hours has the lawn facing stressfully high temperatures in addition to being stressed from mowing. Hot afternoon hours are not good, either. When it is very hot, mow high and use a sharp blade. I recommend 2 1/2 inches minimum, with 3 inches being better. The lower night temperatures, along with an irrigation cycling the following morning, is about as good as it gets for the lawn! In reality, most people mow when the grass needs to be cut, when they are motivated to do so or when they can get around to it because of busy schedules. Grass is one of the most forgiving plant forms to work with. Grass takes a lot of abuse, but when given a little window to recover, it does so with minimal water and fertilizer help.

Q: How close can you plant cedar trees to a house? I am hoping to use the trees as a hedge. (e-mail reference)

A: You can plant cedar trees just outside the overhang of the roof so they capture rain water. If you plant too close to the house, the soil will be too dry unless you are diligent about watering.

Q: We have 15 American lindens. Last year’s dry heat didn’t help them any. The tops of most of the trees are not leafing out. The parts of the tree that are leafing out look sparse. Will these eventually fill back in? Should I prune back some of the dead branches or is it better to replace the trees? (Bismarck, N.D.)

A: I suggest you try to make contact with a certified arborist in your city. Go to for a listing to select from.

Q: I live in the Boston area. I have a mock orange that gets full sun and is planted in sandy soil. It is growing normally, but it never flowers! What’s wrong? (e-mail reference)

A: Lack of flowering is due to many factors, such as too much nitrogen or shade, lack of hardiness of the flower buds or the buds were teased out of hardiness early in spring only to be killed off by a hard, late frost. Give it another year. If none of this applies and if it doesn't flower for you, rip it out and replant with something else that will give you a better return on investment.

NDSU Agriculture Communication

Source:Ron Smith, (701) 231-8161,
Editor:Rich Mattern, (701) 231-6136,
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