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Published July 29, 2011, 12:00 AM

Hortiscope: Heat stress causes trees to drop foliage

Q: I planted five arborvitaes in large pots last fall. About a week ago, they all turned brown. However, there is a little green on the exterior layers. The summer heat has been brutal, but I have been watering regularly. Is this just a simple case of heat stroke? Is there anything I can do to save them?

By: Don Kinzler, INFORUM

Q: I planted five arborvitaes in large pots last fall. About a week ago, they all turned brown. However, there is a little green on the exterior layers. The summer heat has been brutal, but I have been watering regularly. Is this just a simple case of heat stroke? Is there anything I can do to save them? (Atlanta)

A: Brutal indeed! The plants will drop their oldest foliage from previous years under this kind of heat stress. This is a way for the trees to protect themselves from dehydration. As long as you are able to keep the soil moist, but not soggy, around the roots and the new growth stays, they will be OK in most situations. It all depends on how long the suffocating heat will last. If the heat continues through August, it could cook several tree species that otherwise would survive Georgia’s summer heat.


Q: I wonder if you can help identify what is happening with our burr oak and hot wings maple trees. The burr oaks have light green blisters on the leaves. They were planted from seedlings about 18 years ago. This is the first year I remember anything like this. The maple had an insect problem with curled leaves and some webs. The hot wings on the maple were being eaten, so we sprayed with a product that was listed as safe for maples. Now some of the leaves have turned brown on the edges. Could it be from the spray or is it something else? I am attaching pictures. We would appreciate any help you could give us. (email reference)

A: It appears there are a couple of problems taking place with both trees. The big one is physical damage from wind action. There also is evidence of iron chlorosis showing up on the oak. This could be due to a high salt concentration or high pH in the soil. I would encourage you to try fertilizing with an iron- based fertilizer if you know that highs soil salts are not the problem. Lastly, it appears that the trees were hit with a spring fungus that the trees have been able to compartmentalize (keep from spreading). In essence, with the kind of season we’ve had thus far, I think these trees will survive.


Q: Attached is a picture of our dogwood tree that we planted a few months ago.

We are concerned with the curling and dryness of the leaves. Some have a little brown on the tips. There is good drainage and no standing water. My wife has been afraid that it does not get enough water and has used a soaker hose around the tree to keep the soil moist, but we still have the curled leaves. Does this appear normal or is the tree stressed? What should we do? (email reference)

A: I’d suggest backing off on the watering somewhat. It appears that the roots are being kept too wet. This also could be a high-temperature wilt that sometimes characterizes newly planted woody shrubs or young trees. The problem is due to an insufficient root system to provide enough water to keep the foliage turgid through the high heat of the day. In most cases, the plants make it through this cycle OK the first year and the symptoms disappear in future years.

Check to be sure that the tree is not planted too deeply. The soil should be even with the crown (root flare) of the plant. If this were the problem, I would advise you to pull the soil back to the flare.


Q: I am hopeful that you could answer a question for me. I have an ornamental crab tree that has been happy and healthy for many years. This spring, it bloomed beautifully. However, around the end of May, the leaves started to fall off. Upon closer examination, the leaves had some brown spots. The fruit then began to turn brown, and now the tree is really looking poorly. Can it be saved?

I love this tree, so I would like to save it from dying. (email reference)

A: This sounds like apple scab. While the tree may appear very miserable right now, with good sanitation this fall and a prophylactic application of fungicide as the leaves are just beginning to open next spring. After that, do another application 10 to 12 days later. This should put an end to this disease. Since your tree has been healthy up to this point, it has enough energy stored in the crown and root system to recover next year. However, continued vigilance is required on your part.


Q: We bought two hibiscus plants at a flea market yesterday. The man we bought them from told us to plant them in the next week. Should we plant them in the ground or leave them in the containers? What do we do about the dead flowers?

The man we bought them from said we could leave them out all year. From what I have read, it sounds like they need to come in during fall and winter. We live in central Illinois and have some bad winters. They are beautiful, so we don’t want to lose them. Can you help? Some of the leaves look bad. (email reference)

A: Hibiscus is hardy in central Illinois, so remove the plants from the container and plant them outside. Simply cut off the dead flowers. The plants should pick up once they are planted and watered in well. Also, give the plants a shot of Miracle-Gro fertilizer.


Q: Our maple tree that we planted almost five years ago did not produce any leaves this year. The buds seemed to start developing, but then just quit. The tree does have a few leaves near the base of the tree. The maple tree next to it has yellow leaves, plus red dimples and black patches. I am wondering if the tree without leaves is diseased and if the disease is spreading to surrounding trees. Would you advise bringing a leaf into a nursery to see what the staff thinks or do you have any other ideas? Any help would be helpful. (Minnesota)

A: Something is killing this tree, but I don’t know what the problem is. The dimples on the leaves are nothing to worry about because they are harmless. You need to contact your county Extension Service office. To find your Minnesota agent, go to http://goo.gl/9PKRz.


Q: I have a question for you about an old weeping birch tree on our rented property. It is early winter here in Melbourne, Australia. The tree has been pruned back severely. All the young branches have been cut back to the thick arms of the tree. We live in a rural area that does not get much shelter from winds. Will it be OK next spring? I love this tree, so I am very worried. Please let me know if it’s fine or if there is anything I can do to help it recover, I am watering it constantly, but as you can imagine, the winds dry out the soil around it. (email reference)

A: The tree should not have been pruned that way, so I cannot say if the tree will recover. You are right to keep it hydrated. I hope that next spring you will get new flushes of growth to bring this tree back to the grace it once had.


Q: We just bought a house with several different fruit trees on the property that have not been well taken care of. The branches holding the pears are breaking. I’m guessing that is happening because the branches are growing almost straight up and down. The peach and nectarine trees were covered with fruit the first time we saw the house six weeks ago. Now these trees have nothing but a few tiny, rotten pieces. I was wondering if you have any advice on trimming and training the pear tree branches and what we could do for the peach and nectarine trees. (email reference)

A: Without knowing where it is you live, all I can do is direct you to someone locally. Contact the Extension Service county agent where you live. Go to www.csrees.usda.gov/Extension to find an agent. If the agent in your county is unable to assist you, he or she will direct you to the land-grant university in your state for a contact who can help you.


Q: I have five catalpa trees in the backyard that I planted at different times during the past five years. Many of the leaves have turned yellow and then dried up to a crunchy dark brown. They have not been sprayed, so the only thing I can think of is either too much water or too little water. I can’t imagine it is too little water because of the wet season we’ve had and the fact that the sump pump hose runs out there. Could the sump pump water be causing the problem? We had the same problem on a smaller scale last year, but they came out of it. I have some planted at another house that are dark green and blooming. I am seriously considering taking these out if I am going to have this same problem every year. (email reference)

A: Your analysis sounds pretty much right on the mark to me! Sump water continuously flowing over the same spot can wipe out a woody planting in one growing season by creating anaerobic conditions in the root zone. If you can’t move the sump water discharge to another location on your property, you will continue to have this problem.


Q: I was hoping you could help me with a problem I have with a Colorado blue spruce. I have a lot of them on my 5-acre yard, but only one that smells bad.

The tree has a very strong cat urine smell. Unfortunately, it is the closest one to our house and pool. It even makes the house smell when we have the window open. Is there anything we can add to the soil to fix this problem? My husband is very much against cutting it down, but I am embarrassed when people come over. Can you help? (email reference)

A: I’ve been answering horticultural questions for more than 26 years and this is the first time I’ve encountered this question! Needless to say, I don’t have a set answer for you. However, in doing a little exploring on the Internet, I did find what appears to be a reliable source of information on this problem. Go to http://goo.gl/hsUuZ and see for yourself. Other than this, everything else seems to miss the mark. I might question if your tree really is a Colorado spruce because white spruce trees sometimes have a reputation of having a cat urine odor to their foliage.


To contact Ron Smith for answers to your questions, write to Ron Smith, NDSU Department of Plant Sciences, Dept. 7670, Box 6050, Fargo, ND 58108-6050 or email ronald.smith@ndsu.edu.

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