Questions on: Cotoneaster
Ron Smith, Horticulturist, NDSU Extension Service
Q: My mother has a beautiful cotoneaster bush next to her house that will need to be moved. I believe it is about 10-15 years old and has been kept trimmed to about 4 1/2 tall by 4 feet wide. She's very sure it won't survive a transplant, but I'd like to get your opinion just in case it's worth trying. How extensive are the roots? Do they spread out or go down deep? (Lisbon, N.D.)
A: She is right. The chance of surviving a move this far into the season is very slim to none. She is better off with a new plant. The roots spread and go deep after this many years of growth.
Q: I have a large cotoneaster hedge that is getting too tall for me to trim. I would like to cut it down and have it start from the bottom again. Could you tell me how far down it should be cut down and when is the best time to cut it? (Ellendale, N.D.)
A: Cut it down as low as you can reach, and get it done before new growth breaks.
Q: I have a case of fireblight in my cotoneaster hedge. We've been cutting out the diseased parts with a trimmer and sterilizing it before each cut. Will this get rid of the disease? Or, do I have to cut it completely back to 4 inches and spray it with something? I hate to start over when it has reached the height and fullness I desired, but it is 20 years old and I'm not sure what their longevity is. (Kulm, N.D., e-mail)
A: You are doing the correct thing, cutting the hedge back, about 12 inches below the fireblight canker. I recommend a heavy cut back only when the disease is completely debilitating to the hedge. You should also be applying an antibiotic to the hedge--streptomycin, or a fungicide containing basic copper sulfate--next spring prior to bud break. Continue to spray at intervals of five to seven days until bloom is completed. During the summer prune out immediately any diseased shoots that show up. Don't fertilize! This only encourages lush growth that is susceptible to the bacterium. If you fertilize your lawn adjacent to your hedge, give yourself a clearing of about 10 feet with no fertilizer going down. Cotoneaster are one of the more susceptible species to this disease, so it will require careful monitoring and management on you part.
Q. Can you tell me what the problem is with my cotoneaster? They are turning brown in early summer with dried up leaves. (Tappen, N.D.)
A Your problem is threefold: one, fireblight, a bacterial infection that shows symptoms of toasted leaves beneath a Shepherd's crook on a branch; two, oystershell scale; and three, Leaf Spot fungus, the brown spots on the leaves not hit with fireblight.
Now the $64 question: What to do? Well, any one shrub that has all three of these maladies should probably be taken out. But, for the fireblight, try pruning out affected branches and spraying with bordeaux mixture. For scale, spray in spring before leaf-out with dormant oil. And for the leaf spot, spray with Daconil 2787, an all purpose fungicide.
Q. Could you please tell me what the lumps and brown spots are on my cotoneasters and what to do with them? (Glyndon, Minn.)
A. The cotoneaster, I suspect, was hit with contact pesticide, perhaps Malathion a on hot day, or the water table is high enough that it is killing off some of the roots due to anaerobic (oxygen-less) conditions. These are just guesses, but overall I don't believe you have anything to worry about as the new growth on your sample is looking very healthy.
Q. I have a hedge of cotoneasters that I planted several years ago from volunteers I found on my lot. This hedge goes across the back of my property for the purpose of a privacy shield. It borders on the vegetable garden so it gets plenty of water. The problem I am having is that it seems to be plagued with fire blight. I have tried cutting out the affected branches which has helped some but by no means solves the problem. I am also reluctant to spray since it borders on my garden. Should I just start over? I am also wondering if you can still purchase Dakota Gray Turban squash seed. (Crosby, N.D.)
A. I would suggest tearing out the hedge and replacing it with the Tallhedge buckthornRhamnus frangula `Columnaris'. My woody plants book from Alberta, Canada, lists it as a shrub that gets 6-8 feet tall so it should make it in Crosby, N.D.
For the squash seed, try Holland's in Moorhead, Minn., at (218) 233-6131.
Q. What can we do to save our cotoneaster hedge? Most of the branches are very rough (scale?) and the leaves get discolored. Some of the leaves are light green like they are lacking nitrogen, while others are small and curled on the edges. (Sisseton, S.D.)
A. Good diagnosis! Your cotoneaster hedge has one of the heaviest infestations of oystershell scale I have ever seen. It may be too advanced to save the hedge, but here is what I would suggest. Cut the hedge to the ground early next spring before leaf out. Spray the stubs with dormant oil and lime sulfur. As new growth emerges over the following months, spray once a month with Orthene, a systemic insecticide that will control any new invaders! See if that works. If not, dig up and replace!
Q: We have a cateoneaster hedge, and we are wondering how to properly care for it. (Carrington, N.D.)
A. With the hedge, you can cut it back to the ground next spring and it will shoot up new growth again.
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