Ron Smith, Extension Horticulturist, NDSU Extension
A: Rust on roses has to be taken care of by one of two methods. You can use preventative sprays or get rid of the alternate host, which are junipers. The latter is the better method to follow, but you don't have to dig out all of your junipers. Survey your property to see if you can find the fruiting bodies of the rust on the junipers. Do the survey this winter or in early spring. The rust is an obvious brownish orange. Pick off the fruiting bodies and destroy them. This breaks up the cycle of what is known as cedar-apple rust disease.
Q: There are wild roses growing in a corner of my garden, which I love. However, for the past two summers they have been cursed by what looks like spatters of bright orange paint followed by the browning and drying of the leaves. Do you know what this might be? (E-mail reference)
A: What you are seeing is rust fungus on the foliage. When the pathogen starts to appear, pick off and destroy the infected leaves, and spray with a fungicide containing mancozeb (Dithane) or simply spray with lime-sulfur. If the roses are still dormant at this time, spray with lime -sulfur. Repeat the application as weather conditions warrant.
Q: My rose bush has some kind of growth on it. They are bumps that begin small but grow to about 2 inches in diameter. They are mostly round but some are oval. They grow on the lower branches and are hard to break off so I have to twist or cut them off. I cut one open and it seems to have tiny holes in it as though something was living in it. I have cut green ones open and found nothing. They change color along with the twig it is attached to which is green in summer and brown in winter. What causes them? The rose is a pink grootendorst and about 20 years old. I cut it down to about two feet in early spring. It gets about 5 feet tall and by mid summer is full of blooms. I never cover any part of it for winter. (Regent, N.D.)
A: It sounds like the rose is suffering from crown gall bacterium, which in this case is soil inhabiting and will be permanently with the plant. The bacteria (Agrobacterium tumefaciens) produces a compound that stimulates rapid cell growth in the plant causing gall formation on the roots, crown and sometimes on the lower branches. The gall is seldom lethal. Itís more of a disfiguring problem. Another gall, caused by a very small wasp, produces what is known as the mossy rose gall. That might have occurred on your bush in some cases, but they usually disappear after a year or two with some good pruning. From your description, that doesn't sound like the one. Congratulations on getting such good blooming on your Christmas cactus. You must be doing everything right as far as the plants are concerned or they wouldn't be rewarding you with such vigorous beauty!
Q: We have an old shrub rose in our yard, which I think may be a Harison's Yellow. It blooms in the early summer and has beautiful sunshine yellow flowers. Ordinarily this is a healthy plant, but this year almost all of the leaves and buds have dried up. The ailment worked its way up from the bottom of the canes to the tips so that the only green left on the plant is on a few branch tips. I did not see any insects on it and have not been able to identify the problem from my gardening books. We have heavy clay soil and the rose ordinarily does fine with very little supplemental watering. Do you know what would cause this problem, if the rose will recover, and if there are preventative measures that should be taken? (Fergus Falls, Minn.)
A: Sounds like it could be stem canker or root rot. Check for canker on the stems first, as that is my strongest suspicion. It might just need a good cutting back to healthy tissue, some water and fertilizer, and it will be OK. Otherwise, if it is root rot, it is a goner.
A: Yes, unfortunately. This rose crown gall, caused by a bacterium. No cure, so the infected stock has to be dug out and destroyed.
Q: I have several questions that came up this growing season:
1. Our new house came with three overgrown and neglected crabapple trees, the pruning of which triggered what appears to be fireblight. I optimistically and lovingly planted and pampered an expensive new rosebush, not realizing until later that roses are related to apples. It turned brown and died within several weeks. Is there any way to grow healthy roses in our yard?
2. We collect rainwater from the roof and use it for houseplants as well as the garden. Could the blight bacteria be in the rainwater? My kitchen herbs are blackening, and the impatiens outdoors are also showing brown leaves.
3. We replaced all the house's old leaky windows with new ones having what they called "low-E" glass. They're wonderful for keeping the winter warm and the summer cool, but I wonder if they block too much of what our houseplants need of sunlight. They seem to get pale and leggy even in the sunniest windows. (Palermo, N.D.)
A: You ask some very good questions!
1. The fireblight bacterium is airborne and therefore present in rainwater. Being a bacterium, it can enter microscopic openings, which plants are full of. Concerning your rose passion, try it again only this time plant in another location, avoid water splashing on the foliage, if possible, and keep it sprayed with a multipurpose fungicide spray or a fungicide containing triforine. Lime-sulfur and Daconil 2787 are two other examples of the many fungicides available for roses.
2. Has your roof been re-shingled in recent years? Could be some chemical toxins coming off that. The fireblight bacterium doesn't infect all plant material, of course. You could also be getting Pythicum fungus started on your plants.
3. You bet! I don't know the range of light that is being blocked, but it has to be within the range that helps produce chlorophyll. There are "spot plant lights" which you can use to overcome this.
Q. What is wrong with my rose hedge? (Jamestown, N.D.)
A. It appears that your rose hedge has something wrong in the root system. Either a root rot, too much water, excessive soluble salts or compacted soil. Try cultivation around the plants and hold off on watering to see if the condition improves. I also might suggest a soil test from around the root area to see what is there nutrient-wise.
Q. What are the black and yellow spots on my rose bushes? I also am having trouble with the leaves curling up, what causes this? I don't want to lose my rose bushes. (Verona, N.D.)
A. Your roses appear to have a couple of problems:
- Black spot--a fungus brought by high temperatures, along with high humidity, rainfall or heavy irrigation from overhead watering.
- Root rot possibility or excess salts in the root zone. I suspect the latter, so be sure that you don't over-fertilize or keep the roses too wet.
Q. What can I spray my rose bushes with? There is something wrong with them. (Linton, N.D.)
A. Your roses have powdery mildew and rust fungi problems. You can control both with either lime-sulfur or fungicides containing triforine (Funginex). Repeat every 10 days, protecting the new emerging foliage. Try to avoid wetting the foliage when watering.
Q. My rose has problems. (Washburn, N.D.)
A. Your rose has an advanced stage of a fungal disease known as black spot. You need to cut back all diseased wood and dispose of it. You also should avoid all overhead watering and splashing when watering. Follow good sanitation and clean up all fallen leaves. Spray with benomyl, chlorothalonil or mancozeb as new leaves appear in the spring and repeated every 10 days all season long.
Q. Enclosed is a specimen from my Patio Rose. It did great until September when it began to slowly die. I did see some of what appeared to be spider webs on the leaves. I sprayed it with Sevin many times, but it continued to dry up. Can you give me any help? (Clifford, N.D.)
A. I could only detect some evidence of downy mildew on the leaves, and some speckling where mites may have fed.
I think that your rose is not dead, but just got zapped by too much stress at the same time. I believe you can look forward to a rebound in 1998.
You should not be using Sevin as your only insecticide. Alternate insecticidal soap, Malathion, Metasystox and Sevin for best control.
Avoid splashing water on the foliage when watering. This will help minimize disease problems.
Thank you for writing and the good sample.
Q. I am sending you samples of what I think are rose bush leaves that are shriveled, stunted and tend to dry up. What kind of rose is it and what is its problem? (Munich, N.D.)
A. All I can tell you from the sample is that it is a wild rose, meaning, an uncultivated type. Since I have no idea what could be causing the problem, and since it appears to be a persistent one, I'd suggest getting rid of it and replacing it with one you can appreciate.
There are several shrub roses available that will be rewarding: "Pink Grootendorst," "Robin Hood" and "Hansen."
Q. I have a problem with a double yellow rose bush. This is an older variety and quite hardy. It blooms faithfully every year, but then the flowers dry up and the entire bush turns brown. So far, it has recovered and leafs out again in a few weeks, and at the present time is green. I am wondering what I can do to keep from losing it. Thank you in advance. I really enjoy your column. (Isabel, S.D.)
A. Having once been a rose fanatic myself, I now abstain from growing any. That statement doesn't answer your question, but it does give a clue to some frustrations in growing roses.
I frankly don't know what would cause your rose bush to react the way it does. I do know that in my younger years when I could keep them looking prosperous, I followed a strict spray, fertilizer, and pruning regime. Even then, I was not guaranteed every year would be a success. When Rachel Carson's book, "Silent Spring," came out, I gave up all the fussing and let them die out. This was back in New York state.
Well, after all this ranting, I advise the following with your rose:
1.Prune the rose plant heavily in the spring while still dormant. Be sure to get all diseased or cankered canes removed. Pick up all remaining leaves. Do this while the plant is still dormant
2.Spray the plant before leaf-out with lime sulfur. This sanitizes the entire above-ground portion of the plant. Apply about cup of 5-10-5 around the base of the plant.
3.As new growth emerges, apply Orthene to control the whole host of insects that ravage roses and, likewise, apply a protective fungicide such as Rose and Ornamental Fungicide, multipurpose fungicide Daconil 2787, or Ferbam--the list is almost endless.
4.When watering, avoid overdoing it, and avoid splashing on the foliage.
5.Fertilize again after July 4.
Good luck! I hope all of this helps.
Q. Could you please tell me what kind of problem I have with my roses? Every year they seem to be getting worse. This year they had very weak stems, so the flowers hung down. The bush didn't get bushy at all. They are planted on the east side of the building. Am I watering too much? I try to water every day, except now I cut back because the bushes look so awful. I only fertilized once this year, but other years I do it more often. They are close to a spruce tree of some kind. I would greatly appreciate some help or advice on this matter. Thank you. (Jamestown, N.D.)
A. Your roses have a bad case of black spot fungus. This is brought on by water splashing, high humidity and poor air circulation.
Cutback on watering to no more than twice a week. Clean up all fallen leaves in the fall. Next spring, after pruning back, spray with lime sulfur and fertilize with two tablespoons of 5-10-5. As the leaves emerge, spray with a fungicide such as Daconil 2787 to provide protection.
Q.I have learned a lot from your Hortiscope column. Please tell me what is wrong with my hansa rose for which I am enclosing a sample. Can you recommend a well illustrated North Dakota weed bookprinted in color? I would like to know the names of the weeds. I am fighting in my gardens.
Thanks very much. (Wilton, N.D.)
A.The chlorosis on the foliage could be caused by a numberof factors: stem cankers, root rot, compacted soil, saturatedsoil, extremely high pH and borers to name a few. My suggestion is to try giving it a couple shots of Miracid (twoweeks apart) to see if it comes out of it. If it doesn't, thenthe cause is likely biotic and needs to be identified.
The best illustrated weed book on the market is one called"Weeds of the West," published by the Western Society of WeedScience. It is printed at the University of Wyoming, the press being Pioneer of Jackson Hole, 132 West Gill Street, Jackson, WY 83001, ISBN 0-941570-13-4. Most of the weeds in North Dakota arefound in this excellent text.
Q. I read your column in the Sun Country every week and the Edgeley Mail when it is there. I would like to know what is wrong with my rose bushes. They grow tall and don' t bloom. I was hoping they would bloom this year. I used to have beautiful roses. Do I have to uproot them and start over? Hope you can help. (Edgeley, N.D.)
A. Thanks for writing and the kind comment concerning the column. It sounds as if your rose bush scion or budwood has died and is sending up growth from the root system which is not the same species of rose. This, unfortunately, happens frequently in our region unless special care is given to these roses. Even then, there are losses on the more tender selections.
It looks like you will have to start over with a new planting of roses. Try to follow care suggestions based on the NDSU Extension publication H-118, "Roses."
Q: Can you tell me how to control black spot in roses? (E-mail reference, Fargo, N.D.)
A: There are a couple of treatments that can be used for black spot control. The systemic fungicide Funginex will get into the plant and protect the new growth coming on, generally with a single application. Chlorothalonil is a contact fungicide that needs reapplication with the appearance of new growth. Generally the procedure for black spot control is to: 1) Clean up all fallen leaves. 2) Avoid overhead irrigation. 3) Avoid overfertilization. 4) Prune out all cankered canes. 5) Spray in spring while dormant with lime-sulfur. 6) Spray when new growth has emerged with Funginex or Chlorothalonil. 7) Give the roses an eastern exposure to help dry the foliage faster and help keep the spores from developing.
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