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Hortiscope

Ron Smith answers questions about plants, trees and gardens.

By Ron Smith, Horticulturist

NDSU Extension Service

Q: I have three goodland apple trees. They are an excellent apple for eating and cooking. However, this year the apples have a brown discoloration in the meat of the fruit. This discoloration looks like the apples have been cut and exposed to the air. What could cause this problem and how I can resolve it? (e-mail reference)

A: Those are channels left behind by apple maggots. Next year, spray the tree at blossom time with an insecticide called Sevin and spray again about 10 days later. You also can get control by purchasing wooden apples that are painted red and have a sticky substance on them. The sticky stuff traps the female when she lands to lay her eggs under the skin. You can purchase pheromone traps that hold the males and prevent them from fertilizing the female. Picking up all fallen apples also will help reduce the infestation.

Q: I browsed your column on cottonwood trees. The only question I found related to my problem was about mites that come from the lumpy growth on the stems right before some of the leaves. I thought they were seedling bulbs that were supposed to be there. This year, I actually inspected the bulbs. I found small insects inside the bulbs. Some would fly out as soon as I opened the bulbs. Can you identify this problem and let me know if there is a remedy? I can get you some pictures if you need them. (Columbia, S.C.)

A: No photos needed. I know exactly what you are referencing. Your problem is the poplar petiole gall aphid, which also is known as poplar leaf stem gall. It is similar to leaf petiole gall, except this problem is on the petiole near midleaf. As bad as they look, they are not lethal to the tree. Generally, a predatory insect population develops and eventually brings the petiole gall aphids under control. No sprays are needed or recommended. If the tree really appears to be going into decline, I would contact an International Society of Arboriculture certified arborist who is competent in plant diagnosis to inspect the tree to see if it needs rejuvenation pruning, root fertilization or injections of trace elements to perk it up.

Q: I've been reading about different trees on your Hortiscope Web page. I have found it helpful in choosing not to plant certain trees. We moved into a new home with a small tree identified as a "weed tree" by a local horticulturist. We are looking at purchasing and planting 10 to 15 trees, so we are wondering what you would recommend. We'd like trees that grow fast and are not extremely messy. However, a couple of flowering trees would be nice. So far, we are planning on two autumn blaze and two paper birch trees. (Alexandria, Minn.)

A: For low messiness, stay away from anything that produces fruit. The flowers are nice and last a week, but the falling fruit seems to last forever and attracts birds. Unless that one week of flowering is important to you, I would stay away from them. Lindens tend to be a little messy as well because of their falling bracts. If you know of a beekeeper who wants to place a hive under your linden, go for it. Linden flower honey is outstanding! A honey locust tree would get my vote. The leaves disperse nicely and the trees grow fast, provide dappled shade and have a nice, yellow fall color.

Q: I purchased 18 emerald green arborvitaes to plant in my backyard that faces a hill. The area gets plenty of sun during the summer. How much space do I need between the plants to create a good screen so I don’t have to see the weeds on the hill? I live in Pittsburgh, so should I invest in burlap? Will I have to spray them before winter? (e-mail reference)

A: I would suggest spacing them about 3 to 4 feet apart to get a quick screen going, but it will take a few years. If you mean by "investing in burlap" that you should cover the plants this winter, the answer is no. There also is no need to spray them. Plant and water in well, then back off as the fall season wears on to allow the plants to harden off before going into a Pittsburgh winter.

Q: I have a willow tree that had three trunks. One fell over during hurricane Ike. Why does this tree wear out chainsaw blade so fast? I’ve cut oak for a whole weekend with no need to sharpen the chain. This tree is close to a creek. I believe the reason the tree fell is the soft ground around the creek. (e-mail reference)

A: My only guess would be that mineral matter might have imbedded itself into the wood when the river flooded in the past. Willow wood is not hard or tough to cut unless it becomes petrified. Trying to cut petrified wood will dull a chainsaw blade in a heartbeat. If you can get someone else to cut up the tree for you, do it! I’ve seen and heard too many horror stories about chain saw accidents. The horror stories come from people like you and me who thought they knew what they were doing. It takes just one slip and a finger or part of a leg can be cut off.

Q: I was able to take a few of my grandmother’s iris plants along with me when I moved. I planted them in front of my house. I had many blooms in the spring, but nothing after that. I figured iris plants were just a spring-blooming perennial. Is that true or should they bloom all summer? Also, they are now “heaving” out of the ground, getting very thick, and I have Bermuda grass in the flowerbed that found its way there from the lawn. I got tips about the Bermuda grass and the heaving from other posts, but since it’s warmer in Kansas than North Dakota, should I wait longer to divide and transplant the iris plants or should I do it now? September usually means 80-plus degrees for us. (Wichita, Kan.)

A: I would say go for it now. You want to have plenty of warm weather for the rhizomes to become established again. Iris plants flower once a growing season, so you are not missing anything. We have a publication that you can download that deals with iris plants. Go to http://www.ag.ndsu.edu/pubs/plantsci/landscap/h113w.htm for more information.

Q: In the summer of 2005, my wife and I planted a row of Black Hills spruce and a row of American plum trees in our farmyard. The spruce trees are doing well. The plum trees did well until this year. I'm not sure what happened. They started losing leaves early in the growing season. I thought a late frost after the leaves were on was to blame. Some of the trees started to green up again from the base, but no upper leaves came back. Would you suggest I dig them out and start over or should I prune them down to the green area next spring? Is it possible the tops will green up again? (e-mail reference)

A: Did this take place with all of the plum trees or just a single tree? It is very unusual for the entire planting to respond this way. Other than some kind of weather fluke, I can't tell you what the problem is. It is unlikely that borers or root rot would have that uniform of an impact. It has to be something external, such as spray drift or herbicide migration, that would cause them all to die. The growth that you are seeing at the base is sucker growth coming from the roots below the graft union. This plant stock is different from the budwoods (scion) that produce the flowers and fruit we find desirable. Before replanting, I suggest finding someone locally who can tell you exactly why these trees suddenly died after getting off to a good start. It might be a good idea to get away from planting anything related to plums in the same area, but it depends on what you can find out.

Q: We love cottonwoods. Along a river that is close to us, we have hundreds of young trees that have grown from seeds. We would love to transplant some of these. How do you tell the difference between a male and female in young trees? Should we dig up 20 trees and wait? (e-mail reference)

A: I don't know how to tell a male cottonwood from a female until they flower. If in five to seven years you find that half of your plantings are female and you cannot stand the cotton, then cut those down and leave the rest.

Q: We have a roughly 50-year-old lilac tree that we love because it provides great privacy and looks beautiful. After we redid our house a few years ago (construction was not near the tree, although the soil in that area did get compacted), two of the tall branches have been ailing. The branches have sparse leaf growth, brownish curled leaves and no flowers. We had to trim quite a bit of the tree in the spring two years ago because a late snowfall broke off a bunch of the big branches. I always hope the ailing branches will get better, but they have stayed in this sad condition. What happened and what can I do? We also have a smaller lilac that has displayed similar behavior. I finally cut it off at the surface because it looked dead. All our other lilacs in the garden are fine, but I have noticed what looks like a fungus on some of them. (Switzerland)

A: Very likely, the soil compaction caused the decline in your lilacs. I would suggest getting a professional horticulturist to come in next spring to do some coring around the outer region of the roots and add some fertilizer. A plant this old can benefit from this kind of attention because the coring gets more air into the root area, which stimulates more root growth and nutrient uptake. While you are at it, get the soil tested to be sure the construction activity has not changed the pH or other nutrient factors in the root area. Fungal diseases can be controlled with the proper fungicide being applied in a timely manner. Again, that horticulturist should be able to identify the fungus and recommend a control.

Q: I have a honey crisp apple tree that is 5 to 6 years old. I have been of the opinion that apple trees produce apples every other year. This tree has produced an abundance of fruit every year. However, this year the fruit is about 50 percent of normal and not as sweet as usual. I am wondering if the lack of moisture this past spring was the cause. I have a probe for watering the roots of my trees and I certainly can do it in the spring if needed. My other problem is grubs. I had them a few years ago. A lot of damage occurred before I got busy with a chemical. I have spread new dirt and reseeded. Now I am wondering if I should spread chemical over the entire lawn every spring for the next three years. If so, when should I do it? Thank you for your expert help. (Fergus Falls, Minn.)

A: The honey crisp apple could be in a regrouping mode for now. See what next year brings. It is unusual for a tree so young to be such a prolific producer of fruit. Grub proofing is done in the spring. Grubs migrate to deeper depths as winter begins to approach. Sometime around Mother's Day weekend is a good time to get the chemical applied because it can be watered in by Mother Nature after the application. It also is the time grubs start actively feeding, which makes them vulnerable to the insecticide.

Q: We live in Alberta, Canada, but not near a city. I cannot find out why the woodpeckers have left many holes in our willow tree. Can you suggest what to do? I would hate to lose this tree. (e-mail reference)

A: In all probability, this is the male woodpecker of the species showing off. You can use scare balloons, Tanglefoot or aluminum pie plates hung from the branches where they are active, or wrap some aluminum foil around the parts of the trunk where they frequent.


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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