July 17, 2003

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: My wife and I recently planted eight emerald green arborvitaes. After three weeks all eight appear to be dying. They are browning in some spots and look stressed. We watered each of them for about 10 minutes after planting and about the same for three of the next seven days. The nursery where we bought them said the effects of overwatering are identical to underwatering. That sounds crazy to me but I don't want to kill what should be a beautiful tree. We have since cut back and let nature provide the water. It's rained about three times in the last two weeks. Should we water more than this or continue to let nature provide the moisture? Should we fertilize? (E-mail reference)

A: The nursery is right. The symptoms of overwatering are identical to underwatering. More trees, shrubs, and houseplants are killed from overwatering than all other problems combined.

Effective communication from the nursery to the customer should be: "water thoroughly upon planting then water thereafter as needed depending on soil and environmental conditions. At no time should the soil/rootball be kept soggy. The plant should be dried to the point of dampness to the touch before a complete re watering takes place. This regime should be carried out at least through the first year. Soil moisture should be monitored closely for the next two years with corrective action taken as needed." Fertilizer will not correct the problem. There is a chance the arborvitaes will recover if you manage the soil moisture as I have outlined.

Q: What can I use to get rid of moss that is growing in my lawn? I have heard that ammonia will work. Is that true? (Pelican Rapids, Minn.)

A: I don't know about ammonia. I do know that the moss will return if you don't take corrective action. You should do core aeration. It will cut down surface moisture, which encourages moss to become established. Pruning the grass will allow more sunlight penetration and air circulation to take place. Plant an adapted species of shade grass such as creeping red fescue cultivars.

Q: I have a question about transplanting lilac bushes. Can I dig some out now and transplant them? They are only about a foot and half tall and are new plants that have come up beside the larger ones. (Jamestown, N.D.)

A: You can give it a try since there is no big investment. Plan to dig them up on a cloudy, cool day and toward evening. Get as much of the root system as you can handle then plant them in the new location immediately and water them in completely.

Q: I have a red splendor flowering crab that appears to be having problems with defoliation. I believe it has apple scab. Also, it appears to have fireblight on some new growth tips and at the flowering spurs. Should we leave the tree alone until winter and look for cankers on the branches or trunk or should we prune out affected shoots? Is spraying with an antibiotic such as streptomycin still recommended to control fireblight? (E-mail reference)

A: Go ahead and carefully remove the infected branches. Sterilize the pruner between each cut. Immediately place the infected branches in a plastic garbage bag and get rid of it.

Streptomycin is still recommended as a control but limit the application of nitrogen fertilizer in the root zone area under and beyond the tree canopy to limit succulent growth.

Q: Is it possible to propagate cinquefoil from a cutting off a mature plant? Are there some written guidelines I should follow? (Bismarck, N.D.)

A: Cinquefoil roots very easily using softwood cuttings (current season's growth). Set up a micro irrigation intermittent misting system and mix in a 50/50 peat/perlite medium. Dip the cuttings in a 1 percent IBA compound. They should root in a matter of weeks. Be sure to cut back on the water after rooting is initiated. It’s a piece of cake in most instances.

Q: I planted three royalty flowering crab12 years ago. In the last few weeks I've noticed the leaves look unhealthy, very spotted and some in various stages of dying out. We sprayed the trees with Daconil after contacting our nursery because they thought it might be a fungus. That was more than a week ago. Since then the trees have lost about a third of their leaves. I see no signs of bugs or worms. (E-mail reference)

A: Unfortunately, fungicides will not cure any disease that has already started to show symptoms. They are effective at preventing diseases from starting and keeping the pathogen from spreading to new growth. The best you can do at this point is to practice good sanitation. Clean up all fallen foliage and fruit. Next spring spray the trees with lime sulfur before new growth begins. Then, as new growth emerges, spray the trees with the appropriate fungicide and repeat in 10 days.

Q: I am having a problem with my potato plants. They are turning yellow at the base. They are just starting to go into the blooming stage. The plants were doing fine up to this point but I did notice the plants were not growing in height the past couple of weeks. They are a lot shorter than my neighbor’s. (Hosmer, S.D.)

A: The problem could be late blight, which is caused by the fungus Phytophthora infestans. This is a disease that is often activated from tubers that have come from storage and were previously infected. The disease favors high moisture and moderate temperatures. Rain, dew, sprinkler irrigation and even high humidity can trigger spore development. Use good cultural practices to control the disease. Rotate the crop away from anything in the family such as tomatoes, peppers, eggplant and, of course, other potatoes. You should do that for at least three years. Plants that don’t have enough nutrients or have other stress problems will be more susceptible to this fungus or the early blight fungus (Alternaria solani). Chemicals, at this point, may or may not work and the effort and expense may not pay off because the outbreak has started. Materials like Bravo, Acrobat, Mancozeb, or others may provide some help. Next year be sure to begin with disease free tubers.

Q: We have an increasing amount of clover taking over our lawn. How do we get rid of it? (Crosby, N.D.)

A: The Ortho company has a chickweed and clover killer that is on the market. If unavailable, try to locate a general-purpose broadleaf weed herbicide that contains 2,4 D and mecoprop. Another option is Trimec. Be careful using these products under and around woody plants. Clover emerging in a lawn usually means insufficient fertility levels. I suggest fertilizing with a complete lawn fertilizer if that is the case. Be sure to water in well after application.

Q: A homeowner in Cando has a couple of juneberry bushes about three years old that are having problems. The juneberries begin developing but then turn brown and dry up. There is a small amount of leaf disease but nothing significant. What could be causing the problem and what could he do to prevent it? (Cando, N.D.)

A: Juneberries are members of the rose family, as are apples and subject to many of the same diseases. In this case, I think the problem could be rust or a fruit rot fungus. The weather has certainly been conducive to the development of the two diseases. There’s nothing you can do about it now except follow good sanitation practices. Remove and destroy the affected fruit and foliage. Next spring spray the bushes with a lime sulfur spray while still dormant. As the leaves open, spray using a Bordeaux mixture.

Q: I've been hearing about a horticultural therapy movement. I think it sounds like a great program. Do you know of anyone in North Dakota who is involved with it? (Bismarck, N.D.)

A: Funny you should ask I have gone through some rudimentary training on horticultural therapy. A book by Simon Straus entitled Horticulture As Therapy is available. I encourage you to pursue your interest in some manner.

Q: My husband got spray happy, so in the process of spraying cocklebur he sprayed my rhubarb patch. He assures me you can't kill rhubarb. For his sake lets hope not! He used trimec. The rhubarb is curled but still green. We have had a great deal of rain. (Ellendale, N.D.)

A: Let me count the ways that husbands can place themselves on thin ice. This certainly has to rank right up there among the top 10! The rain will help. Your husband is wrong, rhubarb can be killed especially with a Trimec product. Tell him to not be so trigger happy next time.

Q: What is the average life expectancy of a silver maple under normal conditions? I have a large one hanging over my house. It’s old so I’m wondering if it's time to cut it down to prevent damage to my roof when it collapses. (E-mail reference)

A: I don't like questions like this. Age has very little to do with the life expectancy of any tree but you are right to be concerned about it collapsing on your house since it is so close. I strongly advise you to contact a certified arborist to do an increment boring of the trunk to find out what shape the tree is in. The arborist may also possibly do some selective pruning. Base your decision on the information that is provided rather than on average age. You will be able to sleep better at night.

Q: I have a Christmas cactus that is in a southern window. During the winter it thrived, bloomed and grew an amazing amount of leaves but seemed to require a lot of water. Now the leaves have started turning purple. It is in a temperature-controlled office with no drafts. What should I do differently? I tried reducing the amount of water but clumps of stems starting falling out! (E-mail reference)

A: It sounds like a trace mineral deficiency so try some fertilizer. Look for something that includes both major and minor elements.

Q: We have two autumn blaze maples in our front yard that have developed little, black spots on the trunks. The spots look like mold. Is there anything we can do? One of the trees has a trunk that is split open near the ground and doesn't look too healthy. The trees have continued to grow quite well despite the problem. The leaves and branches all look normal. (E-mail reference)

A: It could be anything. I suggest having a certified arborist come out and check the trees if they are that important to you. The arborist can recommend a treatment if one is needed or do it for 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: Rich Mattern, (701) 231-6136, richard.mattern@ndsu.nodak.edu