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Published July 03, 2009, 12:00 AM

Spray before, during blooming to save tree

Q: I have read your comments about black knot disease on Canadian cherry trees. What routine care do you recommend to avoid this disease?

By: Don Kinzler, INFORUM

Q: I have read your comments about black knot disease on Canadian cherry trees.

What routine care do you recommend to avoid this disease? The information I have on the tree says it likes sandy soil. I have very hard clay soil. Should I add sand to the soil when I plant the tree? If so, what ratio of clay and topsoil should I use? I never have grown trees before. Are there certain basics I should know about? (Denver)

A: The black knot fungus may not be as serious in your area as it has been in our part of the country. As far as the cherry tree needing sandy soil, it does not. We have thousands of them growing in Red River Valley clay. To prevent black knot disease from getting started, spray the tree before and during blooming with sulfur, captan, thiophanate methyl or any fixed copper fungicide that lists chokecherry on the label. Not all of this may prevent the fungus spores from getting started on your tree.

If the knots should start to show up, carefully prune them out by going back at least 6 or more inches from the visible site of infection. If necessary, cut the entire branch off to avoid leaving a stub. Basic tree care involves watering deeply when needed. On a new or young tree, it is critical to pay attention to this more so than when the tree becomes established. The soil should be kept moist but not soggy so the tree does not suffer drought/heat damage.

Q: I have learned much about my hibiscus tree. I was planning to repot it until I read not to because it loves to be root-bound. How do I know when it is too root-bound? There is a 1-inch root emerging from the top of the pot. I added 3 inches of potting soil and some petunias. Is this OK? (e-mail reference)

A: It shouldn’t hurt a thing. By the end of this growing season, I would suggest taking the petunias out and repotting the tree into the next larger-sized pot.

Q: I was given a hybrid lily plant as a door prize. It had a beautiful orange flower on it that looked almost like a tiger lily. A couple of days after I got it home, it started to look like it was dying. It came in a very small pot, so I transferred it to a larger pot. That didn’t help. Now all the leaves are dying. Is there anything I can do? (e-mail reference)

A: I assume you live in an area of the world where summer is slowly approaching.

If so, move it outdoors into the garden to see if it recovers. Lilies usually are tough as nails, so don’t be quick to give up on it. However, don’t pamper or push it along with too much water or fertilizer. If it is going to make it, it will do so on its own.

Q: I have conflicting reports as to when the best time is to move or take a root from a fern peony. One source says spring is the best time, while another says fall. I’m confused. (e-mail reference)

A: Depending on where you live, peonies usually go dormant by late July or August. When finally dormant is the time for you to divide or take a root.

Q: I have a 4-year-old butterfly Japanese maple. This spring, I have noticed many ants are on the tree. Should I be concerned? What can I do to prevent damage? I also noticed small sacs that look like they have puss in them. (Ohio)

A: The ants are harvesting honeydew, which probably comes from aphids in the tree. Look closely at the new growth and underside of the leaves. That typically is where aphids reside. Get rid of the aphids and the ants will disappear. There are many insect sprays available at garden centers and supply stores that you can use to control this very common pest.

Q: My husband has a dwarf orange tree. It has healthy leaves, but they are full of a syrupy-type coating. When I bring it in the house in the fall, the tree’s coating gets all over the adjacent plants and floor. It also gets black spots on the leaves. Is this a parasite, bug or disease? How do I treat it so that I will get flowers and fruit? The tree has not produced flowers. (e-mail reference)

A: Something is causing this syrupy material to flow. The problem could be scale insects, spider mites or aphids. The first two are difficult to see unless one pays close attention when checking over the tree. Aphids are rather conspicuous.

The black spots probably are a fungus growing in response to the rich carbohydrate material exuding from the tree. If it is not producing any fruit or you don’t consume the fruit it produces, you can use Ortho Max Tree and Shrub Insect Control. Its active ingredient is imidacloprid, which is absorbed throughout the vascular system of the plant, so it kills anything that feeds on the tree. It should be available in most garden center outlets.

Q: We have had a flowering plum tree for about seven years. Every year it blooms beautifully and bears small fruit. At the end of last year, we noticed one of the branches was oozing sap. This year, the bottom half of the tree bloomed, but the top half started and then stopped. Is there anything I can do to save the tree or is it beyond hope? (e-mail reference)

A: This is strong evidence of borer damage. You are correct in the assumption that the top half is dead. Generally, when this much loss has taken place, the tree is not worth trying to save. It never will add to any architectural beauty in your landscape. There very likely are other borer eggs hatching or eggs are being laid in other parts of the tree to carry on the damage. Sorry!

Q: My gloxinia has grown top-heavy, so it almost looks like a vine. The leaves are green, but turning under. What have I done wrong? (e-mail reference)

A: You probably overfertilized it or the potting soil was too high in nitrogen.

Q: Can I dig up some of my daylilies and transfer them to a different location or should I wait until fall? If moved, will they flower this year? (e-mail reference)

A: My experience with daylilies is that they will tolerate being moved at this time. They may or may not flower. If they do flower, it will be sparse.

Q: I planted some rhubarb that was divided from other plants. Can I use some of the stalks this year or should I leave them alone? The plants are full and bushy. Thanks in advance for your time and advice. (Kamloops, Canada)

A: At your location, you would be safe in using some stalks sparingly this year, but don’t go beyond the middle of July.

Q: I have a June-bearing strawberry plant. It is very large and lush, but there are no blossoms. The plant does keep producing offshoots. How can I force the plant into blossoming or will I have to wait until next year for it to bear fruit? (e-mail reference)

A: In most of the northern U.S., strawberries are in their final phases of flowering or just starting to set fruit. It sounds like you have it growing in very rich soil because it is producing so much lush growth. If you’ve been fertilizing, stop doing it. If the soil is naturally fertile, you might want to consider moving the strawberries to another location that gets full sun and not so much nutrient density. If the strawberries haven’t flowered yet, they probably won’t this year, so you won’t get any fruit. There is a good possibility they will next year because they have been in the garden for at least a year.

Q: I’m having a problem keeping up with the weeds in my strawberries. I think the weeds are mostly grasses. Is there any chemical that I can use on the weeds?

When should I apply a herbicide? I picked my first batch of berries this morning. They were very good. I have a mixture of different kinds of berries to give me different yield times. Any help is appreciated. (Lansing, Mich.)

A: There is an herbicide called Vantage that takes care of most grassy weeds. In some cases, the weeds get so bad and the berries are so good that you don’t want to give them up, so digging the plants out and totally eradicating the weeds is needed. After that, the berry plants can be reset. Resetting the berry plants or applying Vantage should not be done when the plants are fruiting. Do it after the berries bear fruit or early in the fall.

Q: I planted many irises from another location two years ago. Now that all the flowers are gone, I have found a bulb growing just below where the flower was.

Is this a seed bulb? I also have many African lillies that have popped up in large clumps, and I am afraid they will choke themselves off. When is the best time to separate and transplant and what are the dangers of transplanting? (Bourbon, Ind.)

A: That is the seedpod you are seeing on the iris plants. For the lilies, you can go ahead and divide them anytime. They are tough and can tolerate normal handling and watering in. Any losses should be minimal.

Q: I was hoping you could help me by answering a few questions about planting an Ohio buckeye tree. If I dig 5 to 6 feet down on my property, I will hit thick shale. Is that deep enough for the roots or do the roots need to go deeper? My neighbor has an above-ground septic system about 100 feet from where I want to plant the tree. Will the roots get into his system? How far will roots travel to find water? (e-mail reference)

A: You are safe on both counts. That is deep enough for the roots of a buckeye and 100 feet is more than an adequate distance from the septic system. For future reference, tree roots do not go “looking” for water. If there is no water, the tree will die. If they are watered from rainfall or irrigation, roots follow the path the water takes.


Gardening or houseplant questions can be directed to: Hortiscope, Box 6050, NDSU Dept. 7670, Fargo, ND 58108-6050 or ronald.smith@ndsu.edu

Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations

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