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

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I was given a fig tree this past summer. It is healthy looking, but is dropping leaves on a daily basis. I have it in a northern, indirect sunlight location. I water the tree once a week and fertilize once a month. Why is it dropping leaves and what can I do to keep it healthy? (e-mail reference)

A: Leaf drop has a number of causes. The most common is too low a light level. Other causes are drafts of dry or cold air and inconsistent watering or overwatering. Generally, watering on a weekly schedule, especially during the winter months, is not advised. It should be done based on testing the soil by feeling for any moisture in the root zone. I suggest you start with the lighting. Get a plant light or two and set them on a 12-hour cycle. Water the tree only when the soil is almost dry about an inch or two below the soil surface. As for fertilizing, do so only when new growth is beginning. Following all these tips, the leaf drop situation should stabilize in a few weeks.

Q: The roots of my oak tree are growing above the ground. Can I cut off one of the roots or will doing that kill it? The root is growing toward my house, so I am afraid of foundation problems later. I’m not sure what type of oak tree it is. (Houston, Texas)

A: It could be a Texas live oak. It is common in the Houston area. I would encourage you to seek out the advice of an International Society of Arboriculture certified arborist to pass judgment on what roots, if any, should be removed. The arborist would understand the support the roots are providing and be able to make a decision as to whether such removal would make the tree a property hazard. Go to http://www.treesaregood.com/findtreeservices/FindTreeCareService.aspx to locate an arborist in your area. You must be one of the exceptions in Houston because you have a foundation. When I lived in the area, most of the homes were constructed on concrete slabs because of the high water table and the relative ease the area has for flooding.

Q: What is a good chemical to apply on tall grass? The area will be dug up after applying the chemical and then trees will be planted. There are Colorado blue spruce trees on two sides of the site that will be sprayed. (e-mail reference)

A: You can use Roundup, but a temporary physical barrier should be put up between the area being sprayed and the spruce trees. Go to http://www.npal.ndsu.nodak.edu/noxious_weeds.htm for a list of publications on weed control.

Q: I hope you can provide us with some advice. We planted a fern leaf peony in June that looked fine for the first few weeks, but then the leaves started turning yellow. We also put Miracle-Gro on the plant once a week or every two weeks. Did we do something wrong? We are worried that the plant is dying. What should we do now? Will the plant come back after our cold winter? (Toronto, Canada)

A: The fern leaf peony likely is going into dormancy. If you did anything wrong, it was overfertilizing. Fern leaf peonies typically don't need more than a shot of fertilizer at planting time and then just once a growing season after that, if at all. Unless the peony is in an open and exposed location where snow cannot accumulate, it should survive. I'm fairly certain that there is a peony society in Toronto. Some of those folks probably will be better able to assist you locally than I can. A site visit is necessary to make an accurate determination of what is wrong with the plant.

Q: Do you know the best method or a method of getting rid of moles in a lawn or garden? (e-mail reference)

A: Moles or voles? Moles are grub eaters and subterranean. They tunnel just below the surface of the soil. Voles are a type of field mouse that are not very bright. Voles eat vegetation and love what we grow in vegetable and flower gardens. A mouse trap where they run will take care of them. Poisoned seeds also will do the trick. Moles are not that common in our state. However, if you do have a mole problem, there are traps specifically designed to catch them. The other big difference is that moles eat and run. Moles don't hang around to raise a family the way voles do, so my bet is that you are dealing with voles. (e-mail reference)

Q: Around the first week in August, I noticed some tiny, red bugs on the stems of my yellow daisies. Now the leaves are shiny and dark. I'm wondering if this is an aphid and the shiny stuff on the leaves is excrement from them. I would like to know if I should spray the flowers and with what? (e-mail reference)

A: You are correct in what you assumed. You can spray the daisies with Sevin, Malathion or Orthene to get the aphids out of the picture for now. You don't want them to get a fresh start on your plantings next spring.

Q: I e-mailed you once before about my dieffenbachia having slow to no growth at all. Since then, I have found out that the plant is a tropic Marianne and realized it wasn't getting enough light. I placed the plant closer to the window to give it additional light in the evening. The plant is growing beautifully. Furthermore, I think an additional reason the plant wasn't growing was because it had spider mites. I discovered mites about five weeks ago and have since treated them with pesticides and a home remedy of soap and water. I’m telling all of this to you because of what I am seeing now. After the mites disappeared, I assumed the problems were over. During the past couple of weeks, I’ve noticed that the very tips of the leaves are turning brown. At first, it was only one leaf and I thought nothing of it. However, more leaves have turned brown at the tip. I thought it was because of the cold, but the temperature in my room is pretty constant at 72 degrees. I thought the plant is being watered too inconsistently, so I purchased a moisture meter. In addition, I have noticed yellow spots on the leaves. The only consistent characteristic about the spots is that they are not translucent. On some leaves, they are faint yellow, grouped spots near the tip and midrib. On other leaves, the spots have more distinct circles. Is this a bacterial or fungal infection? Is it related to the brown-tipped leaves or am I overwatering? (e-mail reference)

A: By your e-mail address, I assume you are at one of the state universities in the country. I suggest that you make contact with the plant diagnostic lab on campus and ask if you can bring a leaf sample over for analysis. Also, bring along the information you provided me. That would be the most accurate way to get this diagnosed. All I would be able to do is come up with some probable guesses based on what you have told me.

Q: Last spring, I planted a row of Colorado blue spruce trees under fabric. I water using a drip irrigation system, which also waters many other deciduous trees. During the summer, the spruce trees started to turn a lighter green and have stayed that way. I have maintained slightly moist soil around each tree. I would like to get the trees back to their typical darker green. I'm thinking maybe I've overwatered. The most water they ever got was during July, when we got almost no rain and had very hot temperatures. I also planted lilacs, honeysuckle, crabapple, green ash, elm and apricot trees and all are doing well. I did have a small insect problem on the deciduous trees, so I sprayed some Tempo on all the trees, which took care of that problem. (e-mail reference)

A: Something other than overwatering probably is causing the light green coloration if what you say about the amount of water being applied is correct. Can you get someone from the local Extension Service office to look things over? The spruce trees are planted too deeply is my initial guess. That would cause the overall lightening of the foliage, but I could be mistaken. The Tempo may have been applied at a temperature that caused the spruce to discolor, but that isn't very likely.

Q: We planted a row of 12 emerald arborvitaes along our property line for privacy in April 2006. They were doing fine until somewhere around the end of June, when three of them turned brown from top to bottom, but the leaves are not drying out. We now have two more that are starting to turn brown. I looked for bagworms, but didn’t find any. Will they recover or should I cut them down and replant? (Toledo, Ohio)

A: Heavy rains in the area may have affected just the trees you mentioned for some reason. Did the water migrate to that location? Those particular trees may have been planted too deeply. It could be that chemical drifting or migration through the soil or air affected just those trees. Another possibility is that reflective sunlight is hitting those trees and causing the dehydration/desiccation. Also, check for root rot or other vascular pathogens. You may want to contact Ohio State University's horticulture department or your local Extension Service office for advice.

Q: We have a farm and would like to plant some of the fruit from our flowering crab. How do we do that? (e-mail reference)

A: This comes under the classification of "piece of cake." Take the fruit and plant it where you want to start seedlings. The fruit then rots and the seeds go through the needed cold treatment during the winter. You should see germination taking place next spring.

Q: We love rhubarb, but are moving to Easley, S.C., next summer and heard that it doesn't grow there. Is there a special soil I could use and possibly plant it in a large planter, such as a whiskey barrel, or does the high humidity and hot weather make it impossible to grow? I even would be happy with small, dinky stalks. (e-mail reference)

A: I don’t know anything about the climatic conditions in that part of the state. You may be right that the heat and humidity may be too much for the plant to survive. Rather than taking a guess from me, contact the South Carolina Extension Service. Go to http://www.clemson.edu/extension/counties1.htm and click on the county where you will be living for the contact information.

Q: I have a question about a disease that appears to have attacked our crepe myrtles. All our trees, except the most vigorous, are affected. A branch suddenly will wilt and die from an older section of the trunk to the tip. A wartlike growth forms around the trunk and from that location the die-off occurs. After I take the bark off the wartlike growth, there are many small insects that scurry about the trunk. (Winston-Salem, N.C.)

A: This sounds like a bacterial gall that apparently spreads easily in your climate. The insects are attracted to the decaying and somewhat sweet matter in the gall. I would encourage you to make contact with the Extension Service at North Carolina State for advice because this plant species does not grow in North Dakota.

Q: I have had two arborists come out to look at our trees. The first one said my problem is two-lined chestnut borer. The second one said I had oak wilt. The tree probably is beyond help, but I am not sure how to protect my other trees. The sick tree is dropping a lot of leaves. Some of the leaves do look like they have symptoms of oak wilt. There still are very healthy-looking parts of large branches right next to completely dead sections. The bottom of the tree looks the healthiest, while the crown is completely bare. I would be happy to e-mail photos if you think that might be helpful. It is very frustrating, to say the least. The arborist who diagnosed oak wilt wants more than $400 per tree to do an Alamo treatment. He also says that there have been unusual things happening to the trees in our area. I would agree with him from driving around the area. Any insight you could give me would be greatly appreciated. (e-mail reference)

A: A photo may or may not help and both arborists may be right. We tend to see just one cause of decline in our plants. However, many problems may come together on one tree, but we blame the disease that is most visible. Oak wilt may have started, which then attracted the chestnut borers. I admit the investment in an Alamo treatment is pricey, but that is pretty much the going price for mature trees. You have to make a decision as to whether it is worth the investment to save the trees or to take a chance on their possible resistance to the wilt. I consider mature, healthy and attractive trees worth almost any affordable investment to save them.

Q: I have five large bushes under my kitchen window. I’ve had them for three years, but they seldom bloom. Most of the buds turn yellow and fall off. Several weeks ago, the new leaves on one of the bushes curled and turned hard. I cut the bush back and sprayed it with a detergent and water mix, but nothing happened. I bought some environmentally friendly spray, but the growth still is hard and curled. All the other bushes are OK. (e-mail reference)

A: It sounds like it could be a couple of microscopic insects, such as mites on the leaves and thrips on the flower buds, that are causing the problem. Having lived a couple of years in Houston back in the early 80s and worked in the landscape profession, I am well aware of all the possible maladies that plants can develop in the hot, soupy environment of your coastal city!

Q: We bought a house that has a row of arborvitaes that are planted too close together and too close to the house, deck and pool. I'd really like to transplant them, but don't know about the size and depth of the root system. They are tall and in very good health. Is it possible to move them safely and how do I go about it? Thank you for any advice you can give. I live in the panhandle of West Virginia. (e-mail reference)

A: I would suggest hiring a landscaping service that knows what it is doing. The transplanting should take place in early spring before new growth begins.


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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