August 1, 2002

Hortiscope

Ronald C. Smith, Horticulturist
NDSU Extension Service

Q: I have undeveloped lake property with well-established poison ivy. The property has been burned out, Round up applied and it comes back eventually. I am very sensitive to this plant and have avoided any serious injury. Is there any chemical that can eliminate this weed completely or can I control it with other types of ground cover? Ideally I would like to know if there is a way to completely eliminate this plant. (E-mail reference)

A: Hire a professional pest exterminator to do the job. If they cannot kill it with the chemicals they have in stock, nobody can. They can use more potent material than you can purchase and are licensed to handle such material.

Q: I had 4-foot spruce trees transplanted this spring in the shelter belt behind our buildings. They have been doing very well with the new growth in spite of our weather conditions (heat and drought). They were fertilized in June. Also at that time I sprayed them with Malathion. I didn't find any bugs, I sprayed them just in case. They have been watered three times since they were transplanted and are looking healthy with good growth. Now after last weeks extreme heat four of them have a section facing the west where the needles are red-brown. It appears to be the needles just behind the new growth and primarily on the west. This row runs east to west; their mates in a north to south row that have some old trees to shade them don't yet show anything like this. Is this related to the heat and drought? I also have a 12- to 15-foot fir tree that is showing some brown dried branches in an area the sun shines on. It is crowded between a big spruce tree and a bunch of lilacs. Is this also drought and heat related? I have been watering these trees. Is there anything else I should be doing? (Hettinger, N.D.)

A: It could be a combination of factors: severance of the root system from transplanting limits the tree's ability to uptake adequate moisture; the residue of Malathion, an oil-oil base insecticide, could cause the symptoms, and finally the heat/drought combination. All I can suggest at this point is to try to keep the plants watered as you have been, and hope for an improvement in the weather conditions.

Q: I have written you before about the ground ivy I have in my lawn. You recommended Trimec. We have used it at least three times already this year and it does not kill the ground ivy. I use a hand held sprayer and even use more than the recommended amount of trimec. What else can we do to get rid of it? (Napoleon, N.D.)

A: Never use more than what is recommended, please. In the meantime, don't give up. Hold off applying any more for 30-35 days. Then, with Trimec and a wetting agent, make an application based on label recommendations. This being the end of the summer and beginning of fall, the Trimec will be translocated into the root system of the plant and give you an efficient kill of the unwanted ivy.

A lawn care operator could use Confront, a broadleaf herbicide that is a little more potent than Trimec. It is not available to homeowners. If this doesn't work, then more drastic steps will have to be taken, such as applying Roundup to the lawn.

Q: Can you tell me what ate my onion tops? They were fine one day and the next they were all cut off. Rabbits, Squirrels, something else? (Kulm, N.D.)

A: Rabbits will not go after onions ( petunias, pepper leaves, dianthus, etc., yes). My guess it is squirrels, and likely the red ones. They are the obnoxious of the two breeds, trimming evergreens, cutting down daylilies, gnawing through wire -- anything! I doubt it would be cutworms. It’s too late in the season for them.

Q: A local gardener has a severe infestation of blister beetles, both black and gray ones, on her tomatoes. She just sprayed last evening with diazinon. Will this take care of these guys? Also, she consistently has large numbers of slugs each year. She uses a slug bait once they appear but was wondering about options to eliminate them completely. (Hettinger, N.D.)

A: It should control the blister beetles, but I wouldn't spray anything I would want to eat with diazinon. Sevin is the better choice, and is labeled for tomatoes. Slugs love litter and hiding places like rocks, boards, and low, leafy vegetation. Eliminate as much of that as possible, and that will help. Also, turn over the garden soil in the fall to expose the critters trying to nestle into something that will protect them.

Q: A lady asked me to look at her trees. They are Siberian (Chinese) elm approximately 25- 30 feet tall, with some age of course. Two of them leafed out nice. Now one has lost about half or more of its leaves and one is starting to lose. The third one about 30 feet away is fine. (New Town, N.D.)

A: Siberian elms are racked with disease problems. In fact, it is more unusual to find one that is healthy! The homeowner will have to live with the malady that is attacking the trees or simply remove them to replace with something else. Spraying does little good, and the tree seldom completely dies, usually "surviving" with a branch or two still alive. If she wants to, have her get the healthy tree sprayed with a fungicide for protection by a local arborist. Chinese elms and Siberian elms are not the same; the Siberian elm is hardy in our area and is Ulmus pumula; the Chinese elm is not hardy and is a beautiful, disease-resistant tree with attractive characteristics I could lapse into poetry about. It is Ulmus parvifolia . It is also knows as the Lacebark elm. The principle attribute of the Siberian elm is that it is useful genetically for breeding in Dutch elm disease resistance. If we could grow the Chinese elm in North Dakota, everybody would love it and want to have one.

Q: Could you please tell me how I can start a new hydrangea plant from cuttings of my present one? (E-mail reference)

A: Softwood cuttings root from May, June or July growth; semi-hardwood cuttings will also root with a little help from a rooting compound like IBA. Peat/perlite mix works well, as does a peat/sand mix, both under intermittent mist.

Q: I have a question on transplanting raspberry plants. I have some friends who are not having very good luck with them. The plant had all kinds of green leaves when they received it. They transplanted it and then the leaves dried up after it was in the ground. It had plenty of water. What should they do? (E-mail reference)

A: What you describe to me is a pretty good indication of a dead plant. If they are strong in faith, tell them to leave it and replace it next spring if this one doesn't come back; if they are more realists and want to know now, tell them to scrape the bark at the base with either their thumbnail or knife to see if the cambium tissue is still green. If it is there is still a chance for recovery; if not, then it is history.

Q: Is there any way of stopping or decreasing the amount of cotton produced by mature cottonwood trees? (E-mail reference)

A: Short of cutting the offending trees down, none that I know of.....sorry!

Q: Our willow tree has recently started to get spots on the leaves, then they turn yellow and fall off. Not just one or two, but quite a few leaves. Also there are a few branches on the tree that never got leaves on them this year. They appear to be dead and may need to be taken off. Do you have any idea what could be causing this? The tree was very healthy and hearty for a couple years and now it just doesn't look right. Could it be a fungus? If so how should I treat it? (E-mail reference)

A: The problem is the species. Willows are a plant pathologist's dictionary of diseases and an entomologist's collection of insect problems! The tree is a perpetual problem as it matures on residential properties. You can spray it with Bordeaux mixture for diseases and malathion for insects on a regular basis and it will still die. All you can do is delay the inevitable with a continuous care program until you cannot stand it any longer and have the plant removed.

Q: On our perennial hibiscus, a few fringes of the leaves are curling up and in. I can't see any kind if insects. As of now they are not changing color. The plants are loaded with buds. Do you have any guesses? (E-mail reference)

A: Curling leaves are usually an indication of drought or salt stress. I suggest attempting to keep them well hydrated with high quality water.

Q: Is there any thing a person can spray for ash borers this time of year? There are ash tree rows full of the borer larvae, which are difficult to control at this stage. (Minot, N.D.)

A: What a curse to have on your ash trees!! The way I understand the ash borer cycle, if this is the first year of infestation, the larvae are feeding within the bark and could be vulnerable to a systemic insecticide. Typically, this pest takes two years to complete a life cycle, with the second year boring deeper into the wood, beyond the bark/cambial area. At that stage, no insecticide, systemic or otherwise will have any significant effect. The "hottest" systemic insecticide to control these pests is a product called Bidrin, put out by the Mauget Company. It is a restricted use material, so one would have to be licensed to make the purchase and application. Perhaps a local arborist is licensed to do this injection work and could serve your nursery. Other possible practices are to cover fresh wounds with tree wound dressing to prevent further bleeding and entrance of disease organisms; prune out anything that is beyond saving and burn, and finally if only a couple of trees are infested wrap the trunks and basal parts of the main branches in mid-May with burlap or cotton cloth to trap the emerging moths, removing it in mid-August. Repeat this for three years. I hope something here will help you save your trees!

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.

###

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