April 25, 2002

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: My question is about the effects of potassium nitrate (Greenlight Stump Remover) on adjacent trees. If placed in a hole approximately 4 feet from 2- to 3-year-old blue spruce, will we see some leaching and subsequent damage to those trees? (Hettinger, N.D.)

A: Your question leaves me a little confused: potassium nitrate (aka saltpeter) is used in tree stumps along with paraffin and slowly burned out of the ground. Otherwise it is a fertilizer. Are you placing it in the ground or the stump of a tree? Either way it shouldn't damage the adjacent spruce, unless it is over-applied, and that would only result in localized root damage, not the killing of the whole tree.

Q: I had a homeowner bring in lawn moss on soil. She says it is growing in open area. I usually associate moss in shady damp areas. I found some information from Minnesota to control it with copper sulfate. What else would you suggest? (Ellendale, N.D.)

A: Improve the soil surface drainage, along with core aeration, power raking, and the judicious use of lime. Copper sulfate works but can be toxic to other plant material, grass, as well as woody plants. I suggest the mechanical means first, then the chemicals if that fails.

Q: Is there a systemic insecticide made for borer control in pines that could be poured around the base of the tree and taken up by the tree? Are there any insecticides that would be actually taken up by the pine tree and provide control against borers? (Hettinger, N.D.)

A: The systemics are not effective against tree borers. They are costly, expensive, have a potent LD-50, and give only variable results even when professionally applied. The control for borers is typically topical applications of insecticides like lindane and permethrin (Astro, etc.). Chlorpyrifos (Dursban) is now illegal to use. The problem is timing the application just right to get an effective kill. It can vary from season to season and each microclimate change. Best bet: Select trees and shrubs that are resistant to borers; attempt to select the right plant for the existing environment to reduce stress, which attracts borers.

Q: When is the appropriate time to shape a spruce tree? (Logan County, N.D.)

A: The best time is right after the new growth has finished elongating, then cutting that back about half-way. Generally, spruce need very little pruning, so I advise not doing so unless it is poorly shaped, diseased, or has damaged branches.

Q: We are retired farmers near Aberdeen, SD. Our shelterbelts are quite old maybe 30 to 40 years. Many "residents" there are the old Chinese and Siberian elms that have long since lost favor, but they were the "tree-of-the-hour" when we planted them, as they grew fast and provided much shade, beauty, and wind protection for us all. This winter and spring a weird phenomenon has taken place. Of those that have survived, and in some new growth, many of the tops, perhaps10 to 15 feet, have been completely stripped of all bark all the way around the branch. This spring when these old trees leaf out, we will have most of them showing dead tops, if the whole tree doesn't die. Can you shed some light on what has happened to these old trees? (Aberdeen, S.D.)

A: About the only thing we can be certain of is that the trees will be dead from that point up! It is likely a cause of borer damage along with a canker disease of some kind that girdles the trees.

If you get a chance, you might want to try talking with your local NRCS people to see if they can help you with tree replacement in your shelter belt. I assure you, the Siberian elm will not be a replacement!

Q: If the person with the sweetpotato planting will take cuttings about 3 or 4 inches long and put them in water they will root in a couple days. Then plant them in hills in the garden like any other young plant after all possibilities of frost are past. Sweetpotatoes like mounds of soil. I start my sweetpotatoes like this all the time. Sweetpotato plants are quite expensive to buy so I've learned to make my own. This might be the only plant that roots faster then quack grass. (Gwinner, N.D.)

A: That's quite a reputation, to be faster rooting than quackgrass! Thanks for the information. All the readers will appreciate knowing of your sure-fire technique.

Q: Can you please help with a spider plant? Over the last three years it has developed brown bumps all along the stems. It makes the leaves sticky and has webs in the center of the plant. I have put granules in the soil to kill it and it did not work. I have also tried to use alcohol on it. I am sure I did not get all of it, but it did not work. I sprayed it with dawn dish soap and it is still there. Please, can you suggest something so I do not lose this special plant? (E-mail reference)

A: It sounds like your poor plant has a bad case of scale and spider mites. Usually when they get to this state, you are better off in dumping the plant. However, if you are determined save it, you may want to make up a dip solution that you can immerse the aerial part of the plant in. This would require you removing the plant from the container and washing the soil off the roots completely. Then take a tub or bucket, put in a measured amount of water (1 or 2 gallons). Then I would suggest an organic-based insecticidal product that you could add to the water. This would include insecticidal soaps, Neem-containing products, and pyrethrums. Several companies handle them - Schultz, Safer, etc. Be sure to wear rubber gloves and observe any other precautions indicated on the label. Dip the aerial part into this solution for about 10 seconds up to (but not including) the root system. Allow to air dry for about 15 minutes while you have the roots in a weak fertilizer solution, then repot in fresh potting soil. This may or may not work, but it may be worth a try. Scale is extremely difficult to control when they have progressed as far as you indicate. You might also want to study the aerial parts of the plant to see if there are any sections where scale has not yet invaded, and cut everything else off. In the end, it just may be easier to dispose of the plant.

Q: A jade plant that I've had for over 10 years is in trouble. Since I repotted the plant last winter it has been losing leaves. The leaves are dropping from the bottom up. Some of the leaves are getting a dark brown splotchiness in the center of the leaves and around the edges. (The dark brown has happened more recently, and these aren't the leaves that are dropping. ) I have read that leaf drop can be the result of underwatering. I have increased my watering this past month. I let the soil get dry to the first knuckle, then water. I never let water sit in the dish. The pot also has a white powder on the outside. I have heard this is normal and not harmful. The stems are strong and in good shape. Please help! This plant is very dear to me. (E-mail reference)

A: Something obviously has changed in the plant's environment. Jade has a fairly high light requirement, with a range going from as low as 150 foot candles to as high as 500 foot candles. Usually, leaf drop is associated with lower than optimum light intensity to sustain the plant. If possible, check this out, and add a direct light source that has phyto-sensitive range for plant growth. Too much heat and underwatering - as you surmised - may also cause the same problem.

Second, the white powder on the side of the plant is an indication of a salt build-up problem. But since you've recently transplanted, that should not be the cause of your symptoms right now. Finally, look carefully at the leaf and branch axils (where they attach to the stem). Mealybugs are notorious pests and could be contributing to the decline of plant quality. They can be easily controlled by dipping a cotton swab (Q-tip) into rubbing alcohol then swabbing it onto the pest.

Finally, as Jade is a succulent, adjust your watering schedule to meet the needs of the plant - low requirements for water in winter; more in summer when active growth is taking place but always allowing it to dry between waterings.

Q: I looked at an ash tree today (planted in 1998 and about 8 feet tall) that has numerous holes in it, resembling ash borer holes, and a large fresh hole that appears to be a woodpecker trying to get the borer. With the removal of Dursban from the market, what would be a good product to use? There is also a large branch on this tree, about an inch in diameter, that has this insect damage right at the collar, and it extends at least half way through the branch. Does this sound like something seen with ash borers? I thought they just made the entrance and exit holes, or is there more? (Hettinger, N.D.)

A: The nearly over-planted ash tree is no stranger to problems, both insect and disease. The ash borers have a three-year life cycle to maturity, during which time they can raise havoc with the trees they attack. Apparently this tree is under stress of some kind, so I would take it down and replant with something that is more resistant like the Amur cork tree or Kentucky coffeetree. Your part of the country would support these two beauties easily, and they would offer something that is not commonly seen in our North Dakota environment. Both are virtually trouble-free. If the idea of replacing the tree is abhorrent to your client, then lindane is suggested at three-week intervals beginning around the middle of May. To me, spraying that often with a toxic material like lindane isn't worth trying to save the tree. I would encourage replacement.

Q: Regarding the person in Jud who has a sweet potato that is growing, have you ever planted just the sweet potato? I have, and all that it does is make a very nice plant. There is nothing below ground. That plant should be cut into 6-inch pieces and rooted in moist soil or water. Right now is a good time to do this as they will have nice roots by Memorial Day when it is time to put them out.

A: How I love getting tips to pass on to other readers from practicing gardeners. There is no way I can grow everything, so when a gap exists, it is nice to know there is anecdotal information available on certain cultural practices that have succeeded with people like yourself. Thank you!

Do you have a gardening or houseplant question? Write to Hortiscope, Box 5051, NDSU Extension Service, Fargo, ND 58105 or e-mail to Ron Smith at ronsmith@ndsuext.nodak.edu. Note to e-mail correspondents: please identify your location (city and state) for most accurate recommendations.

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Source: Ron Smith, (701) 231-8161, ronsmith@ndsuext.nodak.edu
Editor: Gary Moran, (701) 231-7865, gmoran@ndsuext.nodak.edu