Questions On: Tree Disease
Ron Smith, Horticulturist, NDSU Extension Service
Q: What kind of help can I give my tree that has twigs with small areas of no growth? Those areas tend not to bud. Some of the branches had black spots at the center. I pruned off those areas. I’ve continued to prune until the exposed areas look healthy. I am concerned about my tree and did not know what to use to stop this disease, if that is what is happening. I think the tree is a pink pussy willow because it has huge, fuzzy buds. (Roseburg, Ore.)
A: The best thing you can do is get the disease organism identified by someone from Oregon State University’s plant pathology department. Its Extension Service branch at the university should be able to provide that service for you and make the proper recommendations for control. You might want to check with the Extension Service office in your county to see if it has a horticulturist or plant pathologist who can advise you. Unfortunately, pussy willows are hosts to a wide range of diseases, such as stem cankers and leaf spots. You can try an all-purpose fungicide, such as Funginex, with the hope that it will stall or stop whatever is causing the problem.
Q: I have several questions about things going on in my yard in north central South Dakota. We had a green ash (Marshall) and cottonwood (Northland) planted six years ago and now about 20 feet tall, which were thriving until this spring, when neither leafed out. I suspect sprayer damage, since others in the yard are fine. Now there is regrowth coming up from the bottom of both. Should we tear the trees out and replant, or prune the regrowth to let just one shoot grow, or if we let them all grow, what will it eventually look like? We have an Autumn Blaze maple, also about six years old, which is 18-20 feet tall. I have no experience with maples and am wondering what the normal leaf color should be during the spring and summer. Ours is pale to bright yellow-green. It seems healthy, but I'm wondering if it is lacking in nutrients. Is columnar buckthorn susceptible to fireblight? Ours has stems on which the leaves have all turned a red-brown, seemingly all at once. The leaves are crispy, and are all still on the branch. This appears randomly throughout one bush, and has killed back entire sections of another. If not fireblight, then what else would be causing this, and how should we treat it? My 20-year-old Hopa crab has, for the last two or three years, leafed out, bloomed and looked healthy until mid-June when the leaves begin to look diseased. They begin to yellow and have spots on them, and by now are dropping in large numbers. It doesn't seem to affect its growth the following spring, but am wondering if this is something we should be treating or ignoring. (Eureka, S.D.)
A: All good questions! I would suggest removal of the ash and cottonwood. Sometimes sprouts will make a decent tree, but 99 percent of the time not. I'm afraid you would only be frustrated.
The maple sounds like a trace element problem. Try applying chelated iron to see if that helps. Often the high pH of the soil messes things up for leaf color development to be proper.
Buckthorn is not susceptible to fireblight, and I don't know what would cause similar symptoms unless it is a bad case of rust. Do you have any oat fields in the region? Oat is an alternate host.
Apple scab is common on Hopa crabs. Clean up fallen leaves this autumn; spray with lime sulfur next spring when dormant; spray with Bordeaux mixture at leaf out, and again 7-10 days later there after; Or, just live with it as you have.
A: Unfortunately from your description, it sounds like your sumac is suffering a death from Verticillium wilt, a soil-borne fungus that affects the vascular system of the plants it attacks, essentially killing it off. This is a progressive, terminal disease. You have a university in Guelph, Ontario with a good horticulture program and, I am sure, an equally good diagnostic lab. Try contacting them to see if they can perform a diagnosis for you. If it is something else that I am missing from your description, maybe the condition can be halted. I would like to be wrong in this case!
A: The silver maple leaf just has some cosmetic galls on the leaves caused by mites feeding in early spring. Nothing to do or worry about. The other two samples, I am not sure. Obviously some pathogen is affecting the lilacs, and it could be downy mildew. The apple showed no pathogens on the sample, so I suspect it might be a canker or root rot problem. It is definitely not cedar-apple rust. I suggest monitoring the apple tree, and if it continues to decline, remove it. The same with the lilacs. You donít want either remaining to act as a vector to spread to otherwise healthy plants.
Q: Can you tell me what is wrong with my tree? The leaves turn brown, curl and then the whole tree dies. (Linton, N.D.)
A: Your tree has anthracnose symptoms, but that alone is rarely fatal. It usually causes defoliation in the early spring, if at all. I think you are witnessing a number of problems: the anthracnose fungus; a root-rot disease; and a soil-borne disease known as Verticillium wilt, which can very effectively cause rapid death of a tree.
Q: Enclosed is a branch from my May Day tree. Can you tell me what disease or infestation is affecting it and what I can do to stop it? I have been trying to prune many of the branches. Also, can you identify this vine that is growing among some wild grapes? (Walhalla, N.D.)
A: Your May Day tree is loaded with cankersfungal diseases which eventually kill off branches, as you have discovered. Sanitation, such as what you are doing, removing the infected limbs is the best approach. You may also try spraying with Bordeaux mixture to help control it.
I am not sure of your vine. It smells like a member of the Nightshade family, but I cannot get it to key out for me. To be on the safe side, don't eat the fruit!
Q: The top of my nut tree has turned yellow during the summer. Can you tell me what causes this? (Sisseton, S.D.)
A: Your tree sample showed heavy infection of a fungal leaf spot disease. Control by cleaning all leaf litter this fall, then spray with lime-sulfur next spring just before bud break. After the leaves unfold, spray with a protective all-purpose fungicide.
Q: A neighbor at the lakes has a black substance on her trees and they appear to be weeping. Would this most likely be sooty mold or a canker? I am going to be looking at them this weekend. Someone at a garden store told her to use Orthene before Memorial Day, which leads me to believe she has a bug problem and sooty mold as a result. (Detroit Lakes, Minn., e-mail)
A: The black substance is most likely black knot, a fungal disease that hits members of the cherry species--Prunus spp. If she wants to save the tree, I suggest using lime-sulfur at a rate of 0.5 pint per gallon of water.
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