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Ron Smith answers questions about flowers, trees, gardens and shrubs.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have 10 Winnipeg parks shrub roses. This summer, the roses were deformed. There were a lot of aphids and some white bugs that could be thrips. The leaves had holes caused by rose slugs or leafcutter bees. I applied homemade insecticidal soaps on a regular basis (at least once a month) to take care of the problem. There also were a small number of green worms or caterpillar bugs. For this, I removed and discarded the infected leaves. After that, blackspot appeared. I was so discouraged by then that I quit trying. Some Internet sites recommend removing the diseased leaves, branches and all ground debris this fall. How do I differentiate between diseased and healthy branches? Until now, I have pruned my roses in the spring. What do you recommend I do for the insect and disease problems and what would be the timeline? Any help you can give me would be appreciated because I am at my wit’s end but hate to give up on my roses. We’ve had these roses for almost 10 years. (Quebec, Canada)

A: What a headache! When roses are healthy, there is nothing like them for beauty, but they can be very discouraging when they are not healthy. Clean up everything this fall as best you can. This would include pruning everything back to 18- to 24-inch-long stubs. This will remove some of the diseased canes and keep the roses from being subjected to wind or snow damage. Next spring, prune out any dead tips that may show up just before leafing out takes place. Also take out anything that is dead or obviously diseased. If you can obtain it in Canada, get a systemic insecticide and apply it according to the directions as soon as the frost is out of the ground. This will limit any feeding activity on any part of the plant. After the foliage has fully expanded, apply a fungicide to protect from black spot fungus and reapply it each time new growth appears, or about every 10 days. Don't give up! These are beautiful roses and are worth the effort to care for them.

Q: I noticed that deer have eaten the leaves off some young lilac bushes and eaten a lot of daylilies almost to the ground. The lilacs already appear to have buds on them. Is this normal? Will the deer feeding on the bushes be a problem? (e-mail reference)

A: Deer eating landscape plants of any kind is not a good thing. The daylilies probably will grow back. These are some of the toughest plants on earth, but even tough plants cannot tolerate continuous deer grazing. Buds on lilacs are normal for this time of year.

Q: I have one orange and one apple tree that I grew from seed, but it took many seeds and many tries. They are about 7 years old. I keep them in full window light in my house. The apple tree is about 1 1/2 feet tall and the orange about 2 1/2 feet. Both have branched off, but neither has grown flowers. How long does this usually take? Do you have any suggestions? (e-mail reference)

A: You must be an incredibly patient woman to nurture trees this long without getting flowers. Did you move them outdoors or allow them to go dormant? Neither tree will produce flowers and fruit until they are mature enough to do so, which yours are not. The age factor is often mistakenly tied strictly to chronological years. You have altered the normal environment of the trees tremendously. This has kept the trees in a juvenile, vegetative and nonreproductive state. I suggest accepting them as houseplants that are foliar in character and not flowering, unless you are willing to attempt stressing them into reproduction. To do that, allow the trees to dry down and/or get chilled or nipped by a light frost. Withholding water to stress them may result in defoliation, as will subjecting them to frosty temperatures. In both procedures, there is risk of loosing them completely. Keep in mind the apple tree is a temperate zone plant, so it needs to go through seasonal changes in temperature and day length. While not a temperate zone tree, orange trees require wet and dry cycles and some temperature fluctuation to be effectively productive.

Q: I am looking for information about cutting roots to keep a plant from becoming root bound. The plant is in a large pot, so I don’t want to repot. I would like to know if I can cut the roots and how to go about it. What soil is best for repotting and do I fertilize the plant before I put it in the garage? (e-mail reference)

A: Altering root volume in containerized plants is done all the time. Cut the roots back to fit the pot. Leave about 1 inch of clear space between the cut ends and the sides of the container. Repot with standard potting soil. You don’t need to fertilize. Give the plant enough water to get the roots in good contact with the soil. The plant will have enough nutrient material present to sustain it until new growth begins next spring.

Q: I gave my mother a pear tree about 25 years ago. It is a Parker pear and produces baskets of huge pears every year. Regrettably, it has become infected with what appears to be fire blight on a couple of branches. Is there any hope of saving it? (e-mail reference)

A: There certainly is! A tree this age is not about to succumb to fire blight. After the foliage drops, prune the blighted branches back well behind the visible symptoms of the disease. Go to a lateral branch or the trunk if necessary. Next spring before new growth emerges, spray the tree with lime sulfur and then with a Bordeaux mixture after the leaves have fully unfolded. Don't push the tree into rapid, new growth through fertilization or watering because that plant tissue is the most vulnerable to this virulent bacteria.

Q: We planted a mountain ash about five years ago on our lake lot. It has not grown or produced any berries. We think the mature oaks are blocking its sun exposure. Would it be OK to move it to a more sunny location? If I can, should I do it this fall or wait until spring? (Battle Lake, Minn.)

A: If this were almost any other tree species, I'd say move it right now. However, mountain ash is such a sensitive tree to being dug up and moved that I hesitate to suggest moving it this late in the season. I think an early spring move with as much of the root ball intact as possible would be a better time. However, move it before the tree leafs out.

Q: I have a maple tree that has been damaged on the trunk. The tree seemed to be dead but had great new growth on the bottom of the tree. The existing branches have not shown any life. The new growth seems to be flourishing, but is this a lost cause? I have used the existing dead branches to support the new growth. (e-mail reference)

A: What you are witnessing is growth from the rootstock, which in this case is OK because it is a hybrid maple and not a grafted one. It will take some skill on your part to prune what you want to keep as your tree. You need to select the strongest and straightest growth and cut everything else out, including the dead parts. The cut stumps might regrow on you. If they do, cut them again and use Sucker Stopper RTU to prevent resprouting.

Q: I have a large mugho pine that is many years old. The branches in some large areas are coated with a white, powderylike substance. On these affected areas, the needles are brown in some places and yellowish on others. This past summer, it looks like the growth stopped on the yellowish branches. Is my mugho dying? The largest portion of the bush looks in good health. This mugho faces south. Please tell me if there is something I can do to get my tree back to good health. (Fargo, N.D.)

A: Unfortunately, mugho pine is susceptible to scale infestation. From what you describe, it sounds like what your plant is experiencing. Depending on how bad the infestation is, there are a couple of actions you can consider. Cut out only the infested branches. Next spring, spray the rest of tree with a dormant oil spray before new growth begins. You also can remove the plant entirely if more than 50 percent of the branches are infested. If the infestation is limited to just a couple of branches, but they are important to the aesthetics of the tree, leave them and spray the pine with dormant oil.

To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or e-mail ronald.smith@ndsu.edu.


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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