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Published July 30, 2010, 08:20 AM

Variety of problems may be afflicting lilac

Q: We have a lovely, mature Japanese lilac in our backyard. Much to our dismay, limbs have started to die. We cut the dead limbs out, but more keep dying. The tree was in our yard when we moved here in 1988. Do you have any suggestions for saving the tree?

By: Don Kinzler, INFORUM

Q: We have a lovely, mature Japanese lilac in our backyard. Much to our dismay, limbs have started to die. We cut the dead limbs out, but more keep dying. The tree was in our yard when we moved here in 1988. Do you have any suggestions for saving the tree? (Fargo)

A: You need to examine the tree closely to try to discover what could be killing the branches. This could be the ash-lilac borer doing the dirty work. Other possibilities are a change in the water table on your property or a nectria canker developing on the stems. If it is insect- or disease-caused, there should be some evidence.


Q: I have 16 coneflowers, but six of the flowers have deformed buds. Could something other than aster yellow be to blame for this problem? (e-mail reference)

A: Generally, no. However, I’m sure something obscure might do the same thing. If it continues to progress, get the coneflowers yanked out. You don’t want the hoppers to be spreading this to other plants.


Q: My cucumbers flower a lot and grow tiny fruits, but then the fruit falls off.

I plant self-pollinating cucumbers in my small greenhouse in good loam that is fertilized with composted cow manure. In previous years, I added compost liberally. This year, I didn’t add a lot. The plants look healthy and do not have yellow or downy mildew. The soil may be too wet. Do I have a nutritional deficiency? (e-mail reference)

A: The fruits that are not fertilized will fall off. I don’t know what else to tell you. It could be a temperature problem. Many times high day or low night temperatures can cause the fruit to abort.


Q: Caterpillars have taken a liking to our young golden willows. They defoliated one tree and have moved on to the surrounding trees. The caterpillars remind me of thistle caterpillars. Are they related? (Mohall, N.D.)

A: These are mourning cloak butterfly larvae. While the adult is beautiful and admired when seen fluttering around flowers, she lays eggs at a rate of 200 to 500 at a time. These gregarious little characters then hatch and begin feasting on willows. After that, they move on to other surrounding trees. Most trees can tolerate an occasional defoliation with no problem. The thistle caterpillar yields the painted lady butterfly, which is a Lepidoptera just like the mourning cloak butterfly, but that’s as far as they go in being related.


Q: I have some red raspberry plants in my yard and want to add some golden raspberry plants. Can I plant them in raised beds about 5 feet apart, or do they need to be at a greater distance apart to prevent cross-pollination? (e-mail reference)

A: You can plant them without worrying about cross-pollination. All raspberry cultivars are self-fruiting. Besides, the pollinating bees would find them if they were 50 feet apart. Enjoy!


Q: What would stop a mountain ash from producing fruit? A homeowner brought in leaves with sun scorch and said the mountain ash wasn’t producing fruit. Other than the scorch, nothing is wrong with the tree. I asked twice about fire blight, and he said it is not present on his tree. (Cavalier, N.D.)

A: The flower buds are more sensitive to low temperature extremes than the foliage buds. My best guess is that your weather killed the buds when they were coming out of dormancy. If they did flower and no fruit resulted, then it again is a weather-related problem. It could have been rainy, windy weather at the time the sexual parts of the plant were ready for fertilization or low temperatures that kept the pollinators from being active. Another possibility is a frost that killed the pistillate part of the flower, making it unable to accept any pollen. One last possibility is the tree getting too much nitrogen fertilizer.


Q: We had several autumn blaze maples planted on our property during the spring of last year. Beginning in mid-June of this year, one of the trees has progressively started to turn red. Based on the advice of the nursery, I’ve fertilized and watered the trees. The other autumn blaze trees also are showing some red coloration. However, the leaves still are predominantly light green, but small in size. I have clay soil and routinely windy conditions. We did have unusually heavy rains in June. (e-mail reference)

A: Maples probably are the group of trees that most commonly exhibit premature fall color because they are sensitive to changes in their environment. When weather extremes occur, maples will show early color. In all likelihood, this is what is ailing your trees. Anaerobic conditions develop when the soil is at saturation or field capacity, which stresses the trees. With clay soil, the problem is compounded even further. Essentially, nutrients are unable to be taken up sufficiently when oxygen is lacking in the root zone. Although not likely, the problem could be from some vascular disease such as verticillium wilt. This is a weak pathogen and is almost never found affecting young, vigorous trees in this manner. If the trees were 25 or more years old, then this would be something to seriously consider.

Premature fall color and yellowed leaves can come from the trees being planted too deeply, especially in clay soil. I hope this is not the case because the nursery planted the trees. All I can tell you to do is wait this out. Check the depth of the trees to be sure the crown (where the stem becomes root) is level with the surrounding soil. Do not water excessively and don’t push fertilization. Allow the soil to dry between waterings. Check the moisture level by sticking your hand into the soil surrounding the root ball. When conditions return to something more normal next year, the trees should perform as you expect them to.


Q: I have some red onions that had green foliage that was getting pretty large.

I read somewhere that I could cut part of the tops off to use for cooking. I also read that cutting the tops off the plants sends more nutrition to the bulbs. Is this true, or have I ruined my onions? I have now read conflicting stories. (e-mail reference)

A: I never have heard of this, so I doubt the validity of cutting the tops off. It might be true if the soil is too high in available nitrogen. If that is the case, excessive top growth will take place at the expense of the roots or the onion bulb. Removing the foliage will not correct this since it is an excess nutrient availability problem. As a guess, I think what you might have heard is that breaking off the tops will increase bulb size, which is false. However, old tales die hard, and that rumor and offshoots of it still abound. Onion bulbs increase in size as sugars manufactured in the top are translocated to the bulb.

If the tops are broken, this process stops and prevents further bulb enlargement. This question comes up often among gardeners interested in growing large onions. You can harvest tender, young onion leaves and use them for cooking.


Q: I started three tomato plants from dried seeds. They contracted the curly top virus. If I can get a ripe tomato or two before they die, I’d like to dry the seeds for next year. Will the seeds carry the virus? (e-mail reference)

A: This virus will not be carried over in the seeds using normal handling and storage procedures. The virus is carried by the beet leaf hopper, which doesn’t feed heavily on tomatoes. The hoppers randomly sample foliage before moving on.

However, even in that brief encounter, the virus will show up in the tomato within seven to 10 days.


Q: I put hardwood mulch on top of black polyethylene sheeting by the side of my house. It has developed artillery fungus, which is making spots on my house.

What can I do about this? Would replacing the polyethylene sheeting with a permeable fabric and red pine needles be a better choice? (Nevis, Minn.)

A: You named it! Doing this also would be better for the health of your landscape plants because they will get more air in the root zone.


Q: I have a question for you about some arborvitae I planted. There are a couple of plants with bent or curved tops. I think they were that way when I purchased them. I planted the arborvitae about three weeks ago. Will they straighten by themselves or should I use stakes? (e-mail reference)

A: Don’t worry because the arborvitae eventually will straighten up by spring of next year.


Q: I have a juniper bush by a window at the front of my home that I would like to trim. Is there a way to trim 2 feet off without killing or harming it? (e-mail reference)

A: Go for it. Just don’t leave stumps and always cut back to where there is some green. Your plant will do just fine.


Q: I purchased and planted two blue spruce trees. While they were being loaded at the store, the very top branch that sticks straight up broke off one of the trees. I didn’t think much of it at the time, but now am worried that the top vertical branch might be responsible for the tree’s growth. I’m not a tree expert, so I could be wrong about how the tree will grow taller. Without the center vertical branch, will my tree have stunted growth? The tree also was oozing a little sap where the top branch broke off. To protect it from insects, I put some tape on it. Should I leave it exposed to dry up and heal? (e-mail reference)

A: First, get the tape off the tree and then stop worrying about the future of the tree. One of the lateral branches, probably the longest one, will curve up and become the central leader with only a little crook in the stem to show for it. In time, the little crook will not be as noticeable. Sap flow in all living trees is normal at this time of year, so don’t worry about that.


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.

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