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Q. "I purchased a sweet olive about 9 months ago. I planted the 20-inch shrub into a large concrete pot that has one large drainage hole, using good organic soil amendments. The pot is in full morning sun and part shade in afternoon. I have been watering the plant faithfully, and have fed it with fish emulsion, seaweed extracts, bone meal, and rock phosphate. With all this TLC, it still hasn't done well. The leaves are small; a large number of them have curled up, turned brown, then fallen off. A few blossoms appeared in early April but soon dropped. What is wrong?"
- D. H, Austin, TX
A. Leaf drop of sweet olive is associated with waterlogged soil, and it sounds like the conditions have been too wet, especially since the planter has just one drainage hole. This plant requires excellent drainage -- allow the top 3 inches of soil to dry out between waterings -- and acid soil conditions. Concrete contains lime, which can leach into the soil and raise pH, which may be a contributing factor in the tree's ill health. If possible, transfer your tree to a plastic container or wooden barrel with several drainage holes. Sometimes it helps to prop the container up on some bricks so the water can drain freely. Use a potting mix with excellent drainage properties. Inspect the plant's roots when you transplant it, and remove any that are clearly dead. Allow the plant to grow a bit before offering it some acidic fertilizer, applied as directed on the product label.
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Q. We have an old white pine tree which has some needles turning brown while others still look quite healthy. A man who takes down trees told us that it was pine blister rust and that the alternate host was gooseberry. We have no gooseberries planted and are wondering if this condition will eventually kill the tree or if it is just unsightly to look at.
- A. R., Freeport, ME
A. "White pine blister rust is recognizable by small orange blisters on the trunk, not necessarily by brown needles. There are so many reasons that a white pine may have brown needles that that symptom alone is not a reliable way to diagnose the problem. Some major causes are environmental -- white pines are intolerant of salt spray (foliage will brown near salted roadways) and air pollution, and the foliage can sometimes be desiccated by dry winter winds in particularly windswept areas. Also, pines shed old needles annually.
White pine blister rust is a two-host disease, and the alternate hosts are Ribes species, including currants and gooseberries. In other words, the disease doesn't spread from pine to pine, but requires an intermediate host. If your pine does have blister rust, it will most likely eventually kill the tree. Unfortunately, there is nothing that can be done to stop the decline.
But, before assuming the worst, I would suggest contacting a professional arborist to come look at your tree."
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Q. Instead of the usual Christmas tree this year I bought a 3-foot Norfolk Island pine. I now have it in a bright, cool room and water it about once a week with tepid water. Most of the foliage is a deep, bright green and it has lots of new growth on it. However, I have noticed lately some brownish needles on the ends of some of the branches. What is causing the browning and what can I do to prevent it from spreading?
- P. W., Weaverville, NC
A. This is typical for this plant, especially in the winter. Usually the needles brown and drop from the bottom up. The air inside our homes is usually very dry in the winter time. You can help the plant along by placing it on a tray filled with pebbles and water to increase the humidity around the plant -- just make sure the plant isn't sitting in water. Also, keep it out of drafts from doorways or heating/cooling vents. Norfolk Island pine likes bright light to semi shade, but little or no direct sun.
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Q. The bark on my young dogwood tree is crumbling off and the foliage is dying. I looked for borer holes but could not see any. The tree did OK last year but was not vigorous. There are lots of suckers coming from the root system -- should I cut the tree back to the suckers?
- S. D., Exmore, VA
A. "Several species of borers do attack dogwoods by tunneling under the bark. Signs of borers include swollen areas on the trunk, usually just above or just below soil line. You may also see some sawdust-like material around the holes or on the ground underneath the holes. However, they are not likely the cause of your dying dogwood. A leaf and stem disease called anthracnose has weakened and/or killed many dogwoods in the mid-Atlantic region. The symptoms include small, purple-rimmed spots or large tan blotches on the leaf, with the entire leaf eventually turning brown. Twigs may die back several inches, or all the way to the main stem. Trunk sprout production is stimulated by the disease. These suckers will be very susceptible to infection, so it's probably not a good idea to try to save those. Trees usually die 2 to 3 years after symptoms first appear. The fungus thrives in cool, moist weather, and since dogwoods prefer to grow in the dappled shade of larger trees, this can create cooler, more humid conditions than in full sun, increasing the disease problems. While this
may not be the actual cause of your dogwood problems, your tree is obviously weakened and stressed by its condition. If it does not already have anthracnose, it will be susceptible to it in its weakened state.
Arborists are not recommending replanting native dogwoods (Cornus florida) at this time, but instead replacing them with similar but resistant trees. Such choices may be redbud (Cercis canadensis ), Cornelian cherry (Cornus mas) or Kousa dogwood (Cornus kousa). A resistant native dogwood variety called "Appalachian Spring" is also a possibility."
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Q. What can I plant near my black walnut trees?
- J. H., Fairborn, OH
A. "Black walnut (Juglans nigra) has a reputation for being allelopathic -- that is, for inhibiting the growth of other plants. Small amounts of a substance called juglone are released by the tree roots, but a far greater amount of this growth-inhibiting chemical is found under the canopy of the tree.
Some plants that are tolerant to juglone include arborvitae, cedar, catalpa, clematis, daphne, elm, euonymous, forsythia, hawthorn, hemlock, sycamore, astilbe, begonia, bellflower, orange hawkweed, hosta, pansy, phlox, marigold, primrose, snowdrop, sweet woodruff, trillium and zinnia.
Avoid plants that are sensitive to juglone, including apple, blackberry, pear, blueberry, asparagus, cabbage, eggplant, pepper, potato, and tomato. Landscape plants sensitive to juglone include azalea, birch, honeysuckle, hydrangea, larch, lilac, magnolia, maple, pine, potentilla, rhododendron, spruce and viburnums.
You can also try growing juglone-sensitive plants in containers filled with purchased potting soil."
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Q. When is the appropriate time to prune an oak tree? I have been told a variety of things. My gardener and arborist say during the "hot" months, and the city says not until October. The shade is killing my grass and it is crowding other trees in my yard.
- L. C., Sierra Madre, CA
A. "Many gardeners believe you should prune whenever the pruning tools are sharp. Arborists, however, have scientific studies to rely upon when deciding when to prune. The timing varies with species and with the effect you want to achieve. In general, large cuts should be made in the late winter or early spring before bud break when hydrostatic pressure is greater than atmospheric pressure (i.e. when the sap pressure is positive). A wound made at this time will cause the tree to "bleed". Although some believe the bleeding to be unsightly, it has a positive benefit in reducing the probability of disease-causing organisms to enter the wounds. In the spring the rate of callus production is more rapid, further reducing the chance of invasion.
Other acceptable pruning times include winter and midsummer. Spring pruning after budbreak is undesirable because the bark is tender and damage to the bark is likely. In addition, the food reserves of the tree are being directed toward new growth, leaving less energy available for wound repair. In areas where oak wilt disease is present, it is especially important not to prune oaks between mid April and early July.
Pruning in the late summer is also undesirable because it interferes with food storage necessary for growth the following spring. Additionally, a number of important decay fungi have been observed to produce their largest numbers of spores during the fall. So, the long answer to your question is -- you can remove dead or diseased branches, or any that present a safety hazard at any time. Crown pruning can be done in late winter, early spring, or midsummer."
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Q. Something has damaged the bark of our young dogwood tree right down near the grass line. Could it have been eaten by rabbits or mice? If so, what can I do to keep them away. Is there any way I can save the tree?
- N. H., Westfield, IN
A. "If the rabbits (or whatever) have eaten a substantial amount of bark, or if the tree is completely girdled, then the tree most likely will not survive. If it is a rabbit or other critter, you might try making a ring of heavy duty wire mesh around the tree and/or using a repellent spray made for rabbits. Since it is a dogwood tree, however, you might look carefully for evidence of earlier borer damage as well, since this is a typical symptom of that.
Finally, it could also be due to careless use of a string trimmer. This is a very common cause of death in young trees. Instead of growing grass right up to the trunk, create a ring of mulch around the tree --that way, you can mow right up to the mulch. This saves labor, reduces the risk of injury to the tree, and will also help the tree by reducing competition for nutrients and water from the grass."
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Q. A dog has peeled vertical strips of bark from our tree. Should we treat the wound with any type of protectant or just leave it alone? Do you think the tree will recover?
- I. C., Piedmont, SD
A. There is no product that helps trees to heal from this kind of injury...only time and the tree's natural healing ability will do the trick. If the tree is very young and has lost a lot of bark, or if bark was removed around the entire circumference, it may not survive. Loss of bark increases the chance of secondary infection by fungal disease. All you can do is provide the best possible conditions for the tree. Make sure it receives plenty of water during dry spells, and mulch the tree out to its drip line to minimize competition for nutrients and water.
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Q. I bought and planted an ornamental weeping birch tree in late spring last year. The tree did well the first year, but this spring the buds that formed were green inside, but didn't open. What happened? Is the tree dead?
- R. B., Pittsgrove, NJ
A. Insufficient water may have been a factor. Any newly planted tree needs attentive watering during dry spells for the first few years, in addition to regular watering the entire first season. Another possibility is that a late frost nipped the buds and the tree will leaf out again in time. If the tree is grafted, there is a chance that the graft is failing. There is also the possibility that there is a pest or disease at work, or that there was some accidental herbicide damage, or salt runoff from a walkway during the winter, or there are constricting support ties on the trunk, or any number of other unusual circumstances. I suggest that you do some detective work, and perhaps consult with the nursery where you bought the tree, to determine the cause of the trouble. In the meantime, make sure to keep the soil moist over the entire root zone, and water deeply when needed rather than providing a light daily sprinkling.
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Q. I am in the process of cutting off all the fireblight-damaged areas on my large pear trees. Will the disease continue to spread, and should I spray a fungicide?
- M. B., Berkeley CA
A. "As the name implies, fireblight causes shoot tips to blacken and wilt -- almost as though they've been burned. It is caused by Erwinia amylovora, a bacterium that overwinters in cankers on infected wood. Therefore, a fungicide -- which targets only fungal diseases -- won't control it. Fire blight is spread by insects, pruning tools, and splashing water. Bacteria enter healthy blossoms under the right conditions. A temperature of 65F or higher, plus a trace of rain or high humidity are required for infection. Because exacting environmental conditions are necessary for infection to occur, fire blight may be very serious some years and appear hardly at all in others. It affects apple trees as well as pears.
Pruning is a good way to keep the disease from spreading. Continue to remove infected stems and branches, cutting back several inches into healthy wood. Be sure to disinfect your pruners between cuts so you won't spread the problem as you're trying to remove it. (Use rubbing alcohol or a 10 percent bleach solution to disinfect your pruners. When you've finished pruning disinfect again, then wipe them dry and apply a little mineral oil to keep the pruners from rusting.)"
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Q. What can I do to get rid of the lichens that are growing on my fruit trees? They are all over the trunks and branches, and the trees aren't growing well.
- H. C., Lake Monroe, FL
A. Moss, algae and lichens often grow on the branches and trunks of trees and shrubs where the air is humid. I would not blame the lichens for the poor growth of your trees. They are a symptom rather than the source of trouble. Lichens are green plants (technically, a symbiotic relationship between a fungus and an alga) that manufacture their own food; therefore they're not parasitic, and are not taking nutrients from their hosts. Instead, they indicate that your trees may not be receiving enough sunlight and that air circulation is poor. You can discourage lichens from growing on trees by pruning the canopy to open the branches to more sunlight and improved air circulation. You can increase the vigor of your trees by fertilizing during the spring when they're actively growing. If your fruit trees are hedged in by other kinds of growth (shrubs, forest trees, etc.) you may do well to open up the perimeter in in the direction of prevailing winds, which will also improve air circulation.
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Q. I have a magnolia tree that is about 20 feet tall and at least 15 years old. Several branches have died -- the leaves turned brown and the branches became brittle. On the underside of many of the living leaves there is a light "dusting" of little rust colored spots. They can be wiped off with a finger. Is this causing the problem? What is it, and how can I cure it? There is no realistic way to wipe it off of all the leaves due to the size of the tree!
- C. D., Myrtle Beach, SC
A. "The symptoms you describe lead me to believe your magnolia is suffering from two things: a canker disease caused by fungus, that has attacked the branches, and mites, that are coating the undersides of the leaves.
To combat the canker, prune off affected branches, cutting back an inch into symptom-free tissue to remove any marginally affected wood. Dip your pruners or saw into a 10% bleach solution between cuts to prevent spreading the fungal spores with your tool. If at least half of the tree shows symptoms, then I'm afraid it's best to replace the entire tree. Less advanced symptoms of canker include elongated, target-like lesions that are blue-gray, and later develop cracks.
Mites and other pests are usually drawn to plants that are already "out of balance," such as your canker-infected tree. Take a look at a leaf using a magnifying lens, and if the "dust particles" have legs, then the dust is probably mites. These pests prefer dry, dusty conditions, and are especially attracted to water-stressed plants. If spring moisture has been lacking, water the tree deeply about once per week. Don't overwater, though, and make the soil sodden, or you'll invite other problems. To get rid of the mites, first try driving them off with a good spray of water from your hose. This will dislodge many of them and also create a humid environment that doesn't favor them. If they are persistent, try a light horticultural oil spray; follow label directions carefully."
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Q. I know mistletoe is a parasite, but where does it come from? Can I just prune it away, or will it kill my tree anyway?
- S. L., Sacramento, CA
A. "Mistletoe is a parasitic plant and heavily infested trees are weakened, often slow growing and usually more attractive to insect and disease problems. Since mistletoe weighs branches down, affected branches often break off in storms or high winds. Prune affected branches out of the trees, making sure to get all of the pesky plant's parts growing within the limb. Mistletoe is an evergreen plant with small, greenish flowers and white berries. Birds carry seeds from the berries, depositing them at random. Sometimes the seeds, with a healthy dose of fertilizer, plop onto a branch and begin to grow."
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Q. I transplanted a weeping cherry tree last fall, but the tree has yet to leaf out this spring. Is my tree dead? The tree is at least five years old.
- M. H., Clinton Twp, MI
A. Transplanting a five-year-old tree is very stressful to the plant, because invariably you end up damaging many roots and leaving many of the delicate feeder roots behind when you dig up the rootball. This means that the plant may not be able to take up the water it needs -- even if you were careful to water it. Trees that go into winter while suffering water stress are also more susceptible to cold damage. Unfortunately, there is a chance that the tree is dead. However, one of the tree's survival mechanisms is to defoliate in order to conserve moisture; it would also defoliate naturally for the winter. So it is possible that it is still alive but is slow in coming out of dormancy this spring, partly because it is still trying to grow roots. Snip off a branch tip and see if there is any green inside the bark, or if it is truly all brown and dead. If the branch tips are dead, work your way back to larger twigs looking for living tissue, since it's possible that the main trunk of the tree is still alive. Trim away
any truly dead wood. If there is live wood above the graft, then the tree may recover. Make sure that the soil is kept evenly moist (but not sopping wet) as you would for any brand newly planted tree until it becomes reestablished.
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Q. What can I do to keep an olive tree from forming fruit, which ends up all over my front yard?
- C. H., Palm Springs, CA
A. One way to minimize fruiting is to prune the tree heavily. By selectively thinning out the fruiting branches each year you can minimize the crop of olives that the tree produces. Carefully inspect your tree and you will be able to determine which branches will flower and bear fruit. They are the smallest, newest branches on the tree. Remove these small branches by cutting them back to the limbs that form the structure of the tree. You'll end up with a picturesque specimen tree without the messy fruit drop. You might also contact a professional arborist to ask about fruit-inhibiting sprays. There are some available for commercial use, but these may or may not be available for home use in your area. All in all, you might be better off replacing the tree with a "cleaner" one.
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Q. I have several 2-year-old apricot and peach trees. I pruned them back last winter and they grew well during the summer. However, the apricot trees now have large drops of sap oozing out of the main trunk. Should I be concerned? What should I do?
- P. M., Tracy, CA
A. "Members of the Prunus family (peach, pear, apricot, cherry) are subject to gummosis. The gumming is a result of mechanical injury, insect damage, fungal diseases, or improper growing conditions. Sometimes it happens because too much water or nitrogen fertilizer have been applied.
You should inspect to see that there are no cankers on the trunks of the trees that might be harboring disease spores. Check to see that there is no insect activity. Once you've ruled out those two problems, then withhold fertilizer and water thoroughly only about once a week so you don't encourage fast but weak growth."
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Q. On two different shrubs in my yard, the bottom banches on one side appear to be dead. (The damaged portions are adjacent.) The rest of the shrubs look fine. I can't find any pest. Any ideas?
- D. P., NJ
A. Usually a distinct limited pattern such as that has a specific cause. You need to be a detective. Examine the tree carefully to see if there is mechanical damage to the branches (did a tall vehicle bump them?) or to the roots (was there root damage by digging on that side?) or was there possibly accidental herbicide damage, e.g. from a lawn "weed and feed" product being spread in a cyclone spreader? If the branches don't leaf out again, prune them off.
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Q. I love the way elm trees look. Is Dutch elm disease still a problem? What are the symptoms and how is it spread? Are there any new elm varieties available that are resistant to Dutch elm disease?
- MD
A. "Although there is no known American elm variety that can be called entirely immune to Dutch elm disease, the following have shown strong resistance to the disease: the Princeton Elm, the American Liberty ""multi-clone,"" and Independence, which is one of the cultivars in the American Liberty multi-clone. Two additional American elms, Valley Forge and New Harmony, have exhibited high tolerance to the disease. Consult with your local nursery to see if they can get the trees for you, or contact the Elm Research Institute, P.O. Box 150, Westmoreland, NH 03467, 1-800-FOR-ELMS.
Up to 100 million American elms succumbed to Dutch elm disease (DED) since the beetle-borne fungus first appeared in elms in the U.S. in the 1930s. The fungus infects the vascular (water-conducting) system of the tree, clogging it and preventing water movement to the crown. The first symptom is often dieback of individual branches from the tip inward toward the trunk, called ""flagging.""
The special features of the American elm -- a stately, vase-shaped, fast-growing, pollution-tolerant tree -- led to its being planted in rows down countless suburban streets. Unfortunately, this pattern of planting also led to its demise. Not only could the elm bark beetles responsible for spreading the disease easily travel from tree to tree, but the disease also spread via the natural root grafts that occurs between adjacent trees."
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