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Q. The new berry clusters on my pyracantha are turning brown and wilting. The plant looks healthy otherwise. Is this a disease I can treat?
- P. J., Vicksburg, MS
A. Pyracantha are subject to two diseases: scab and fire blight. But the symptoms you describe do not completely match the usual progression of either disease. Scab disease will leave lesions on the stems and fruit (similar to apple scab), but it would also affect leaves. Fire blight affects entire shoots, turning leaves a reddish-brown and leaving them hanging on the branch or stem. Both diseases would therefore show other symptoms besides the brown berries. Unless additional symptoms appear, it's possible the problem is cultural or environmental. Perhaps there was a cold snap that damaged the berries or an extended rainy period that prevented insects from pollinating the flowers. You might want to prune off the berry clusters and remove them from the garden -- just in case it is a disease problem -- and then watch the plant closely to see if additional symptoms appear.
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Q. Why won't my zinnia flowers open? The buds just wither and drop before blossoming. Could I be giving them too much water, or too little?
- R. B., San Rafael, CA
A. For good performance, zinnias need full sunshine, warm temperatures, and regular watering. Soak the soil thoroughly when you water, and try to keep water off the foliage and flowers. Zinnias are subject to some diseases, including blossom blight and powdery mildew, as well as attack by a handful of insect pests. Look for signs of fungal infection (brown spots or a powdery white coating) or signs of nibbling by little caterpillars or beetles. If the flowers don't look diseased or eaten, the problem is probably cultural -- not enough sunshine and heat, or inconsistent soil moisture.
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Q. The leaves on my impatiens are turning yellow and some have blackish spots on them. They are in partial shade and have been doing very well until recently. Is there something I can do to correct this?
- D. B., Dimondale, MI
A. It sounds as though your impatiens have developed a fungal disease. This can happen when conditions are too wet or when plants are overcrowded. Disease pathogens need three things to become established: a susceptible host (usually a plant that's under stress), a pathogen, and the right environmental conditions. Your best defense against disease problems is to provide all of the cultural requirements necessary for healthy growth, keep water off leaves as much as possible, and remove diseased plant parts as soon as you notice them. If leaves on the entire plant are affected, it may be too late to save your impatiens. If only a few leaves and stems have symptoms, cut them off the plants to encourage healthy new growth.
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Q. I have a rose of Sharon bush that has been a great bloomer for the last 5 years. This year only half the shrub produced leaves and blooms -- the other half was bare. What happened? Should I trim it to the base and let it grow from there?
- S. P., Sugar Grove, IL
A. It sounds like your rose of Sharon (Hibiscus syriacus) may have suffered some winter kill, which is common where temperatures reach 20F and below. Annual pruning is recommended to keep the shrub in top form and blooming well. It's best to prune in late winter or early spring. Prune the shrub to an open vase shape over the course of a few years, and each year prune branch tips back to a few buds. Frequent severe pruning gives fewer but larger flowers; little or no pruning gives many small flowers. You can prune off the dead branches at any time. Make sure your shrub gets water during dry spells, and it should bounce right back.
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Q. I'm having a crisis with my two new Australian tree ferns. We put them in the ground in a shady spot a month ago and it rained for a few weeks -- and they were very happy. All of sudden, one has brown leaves hanging on the ground and the other one is beginning to do the same although not as dramatically. I've gotten contradictory feedback from the nursery where I bought them. One person told me they aren't getting enough water; another too much. Do you have any idea as to what might be going on and how I can save these plants?
- A. Z., Los Angeles, CA
A. Without actually seeing your fern and the site, I can't say for sure what the problem is, but I would err on the side of "too dry." These ferns need a woodsy, humusy soil that drains well but can retain moisture (like a well-wrung sponge). They should be watered if the soil is dry to 3" deep and benefit from high humidity around the trunk and under the canopy. It is normal for them to drop their oldest fronds every few months.
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Q. I have beautiful azaleas that have been established for several years. Because of the dry summer last year I almost lost a couple of them, but with lots of water and patience they made it. This spring the foliage was a little pale and they had very few blooms. I fertilized them and they are now a beautiful green but have developed ugly wart-like growths on the leaves. Can you please give me some advice and tell me if I am in danger of losing my beautiful azaleas?
- S. H., Henderson, TN
A. You're describing a fungal disease called azalea leaf gall. Eventually the swollen leaves will develop a powdery white coating. These are the maturing fungal spores, so to prevent spread of the disease, prune off the affected leaves now and get them out of the garden. Prune your plants to increase air circulation and pinch or prune off any suspect leaves. Some azaleas are prone to leaf gall and others seem to resist the problem. Plants under stress (which is how you describe yours) are more susceptible to disease problems. I expect that once your azaleas have regained their health, they'll be more resistant to fungal diseases.
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Q. "Two weeks ago, I had a beautiful flowerbed -- mainly dahlias -- on the east side of my house. The area receives plenty of sun and water. One day I saw some pinhead-sized bugs, so I mixed and sprayed the area with a commercial "all-purpose" garden insecticide. In about five days, my beautiful, full bed was no longer. My pansies and ranuculus died completely, but my dahlias seem to be trying to hang on. What can I do to save what's left?"
- J. T., Thedford, NE
A. "It sounds as though your plants are suffering the effects of the insecticide you applied. Many plants are sensitive to certain chemicals and, unless the label specifically lists the plants as being tolerant to applications of the product, it's not only risky, but also illegal, to use it on them. Also, it is extremely important to dilute pesticides according to the instructions on the label.
The pansies are probably beyond help, but because they grow from underground bulbs, there may be hope for the ranunculus. I'd cut the foliage back and wait to see if they produce new foliage. I'd also cut back the dead foliage on the dahlias and remove them from the garden. It's possible the tubers still have some stored energy and can produce new foliage.
Before using any pesticide, identify just what is damaging plants. (In this case, it sounds like you didn't see damage, just some bugs.) Try the simplest and least toxic pest control methods first -- for example, hosing the plants down with plain water next time you encounter insects on your flowers. Water won't have such dire consequences!"
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Q. "I have had good luck starting begonia tubers indoors in early March for many years. Last year I had a problem. The undersides of the leaves had a brown scaly appearance between the veins. Out of approximately 30 plants, only a few flowered, and not abundantly like other years. There were very few healthy buds. Some begonias I purchased at a greenhouse had the same problem. I'm actually not sure if the problem originated with the ones I started or the ones I bought. I don't want the same problem this year. Any suggestions? "
- J. D., Appleton, WI
A. This sounds like edema (also oedema), a physiological problem. It is caused by overwatering and is common on begonias and geraniums. The extra water in the tissues causes corklike patches. It doesn't usually kill the plant, but causes stunting and poor blooming. Since it is physiological, it will not spread to other plants. However, if you don't correct the watering, it will spread on the existing plants. Try growing them a bit drier, and make sure your watering is consistent -- not heavy water one time and sparse water the next.
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Q. Help! I just came back from vacation, and noticed that several of our shrubs are dying. Whole areas of leaves and branches are turning brown. I noticed some spider webs on the plants, but no other signs of insects. What is happening?
- M. K., Simpsonville, SC
A. "Is it possible your shrubs dried out while you were away? Lack of water could cause leaves and branches to turn brown. If the webbing on the shrubs is fairly fine, you may have spider mites. Mites are so tiny, they're hard to see, but hold a piece of white paper under suspected leaves/stems and tap sharply. If mites are there, they will drop off and you can see them moving on the paper. They're usually a rusty brownish/orangeish color. Mites like dusty plants and dry conditions, and a severe infestation can cause the symptoms you describe. They are best controlled with a daily blast of water from the hose. If possible, spray early in the morning, before the sun gets too hot. If that doesn't work, try an insecticidal soap.
Note that pests often attack plants that are under stress, whether it be caused by over- or under-watering, inappropriate sun exposure, or lack of nutrients. Maintaining healthy plants is the best way to prevent pest problems."
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Q. What can we use to prevent rust disease on hollyhocks?
- A. B., Enola, PA
A. "Hollyhock rust is a very common fungal disease. It begins with yellow or orange spots with red centers on the top side of the leaf, along with brown pin-head sized dots on the underside of the leaf. Eventually gray pustules form on the underside of the leaf, and all the spots run together, killing big areas of leaf tissue.
Hollyhock rust overwinters on the basal leaves and old stems of the plant. In the fall, after killing frosts, remove and destroy the old leaves and stems. During the growing season you can remove and destroy infected leaves. Disturbing plants while the leaves are wet spreads the disease, so allow plants to dry before working around them.
Other cultural practices that keep hollyhocks healthy include growing them in full sun, in rich moist soil and making sure they have good air circulation. Another tip is to grow them in the back of the garden with shorter plants in front of them to conceal the damage. Some gardeners grow them as biennials, starting new plants every year, and removing them after they flower in their second season. This keeps diseases from building up on older, weaker plants."
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Q. This spring my peonies developed some black spots on the stems and leaves. Is there anything I should I do now or in the spring to prevent a recurrence?
- R. P., Little Falls, NJ
A. Peonies are occasionally subject to foliage problems. The best defense is to clean up the peony bed each fall, carefully removing all the old stems and foliage and replacing any old mulch with fresh mulch. This should help a lot to stop the re-infection next year. During the growing season, remove any foliage that begins to show signs of infection and avoid overhead watering, particularly in the late afternoon, evening, or at night as damp foliage can encourage the problem to spread.
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Q. The leaves of my zinnias have white spots on them, which seem to gradually enlarge. A few of the plants have died and the others are struggling. What are these white spots, and did they kill the plants? What can I do about it?
- H. B., Brighton, MA
A. "It sounds like powdery mildew, which many zinnias are susceptible to. Powdery mildew appears as a whitish/greyish powder on foliage. It overwinters on living plants, and can be difficult to eradicate. If the zinnia plants are declining rapidly, you may want to simply remove them. It's unlikely you'll be able to control the disease in time for these heat-loving plants to recover and put out more flowers before cool weather sets in.
There are some things you can do to minimize its effects next season. The first line of defense is to grow resistant varieties. Also, be sure to space plants properly for good air circulation, and thoroughly clean up plant debris at the end of the season.
Powdery mildew is unique among common plant diseases in that it doesn't require a wet leaf surface to spread. It can thus thrive during hot, dry weather, which is why you see it appearing in August. The general advice to inhibit the spread of fungal diseases is to avoid wetting leaf surfaces. In the case of powdery mildew, you can actually inhibit infection with frequent sprays of water. Also, examine plants frequently, removing any affected foliage immediately."
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Q. "Last spring I planted a large area of vinca in a sunny area on the front of my property. There is no sidewalk so the planting went right up to the street. This spring, while the plantings nearer the house are growing well, those next to the street look really bad. Last year's growth is nothing but sticks. The area is in full sun. Is this some type of disease? "
- L. T., Piscataway, NJ
A. Because of the plants' proximity to the street, I suspect that road salt has harmed your vinca. Other factors, such as heat reflecting from the pavement and air pollution, could also be contributing to the problem. You might try replacing the vinca with creeping juniper (Juniperus horizontalis), which has demonstrated some tolerance to salt and is evergreen as well as very low growing. This plant will also tolerate the hot and sunny growing conditions a bit better than vinca could.
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Q. I've been planting petunias each year, and in the past they've grown well. Then about 3 years ago, they started dying within about 2 weeks of being planted. I have marigolds, celosia and salvia in the bed too and they live and grow just fine, but for the past few years the petunias have died. I can't seem to find any bugs on them. Could it be a problem with my soil pH? I have some petunias in a planter and they are doing just fine. I love petunias and I miss them in my flower bed!
- A. T., Garber, OK
A. Rather than improper soil pH, I would suspect a soil-borne disease of some sort. (Although it never hurts to run some basic soil tests to check nutrient levels and pH.) Some disease spores can live in the soil for years, so it's wise to avoid planting the same type of plant in one location year after year. You might try adding copious amounts of organic matter to the soil to try to help it recover and establish a healthier microbe population that can help keep disease organisms in check.
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Q. My petunias were attacked by tobacco caterpillars, and my Madagascar periwinkles succumbed to some type of fungus. In the winter months, violas and pansies do great, until the sun and heat burn the plants. Do you have any suggestions for annuals for year-round color?
- D. S., Modesto, CA
A. "Following are some suggestions for seasonal color for your sunny annual garden. Before planting, however, be sure to amend your soil with organic matter such as compost. Organic matter helps loosen the soil to allow for better root penetration, while also helping the soil retain moisture. As an added bonus, it will provide nutrients as it decomposes. Once the bed is prepared, consider planting chrysanthemums for autumn color; ornamental kale and pansies for winter color; lobelia and impatiens for spring color; and zinnias, border dahlias, geraniums, and potentilla for summer color.
Caterpillars can be controlled by hand-picking them off the plants as soon as you spot them, or treating with the biological control Bt (Bacillus thuringiensis). Be sure to clean up any debris in the garden at the end of the season to remove any insect eggs."
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Q. I just planted a standard oleander about a month ago. It seemed to be doing well until about 10 days ago. The leaves are curling and the edges are brown. I also saw a colony of tiny yellow-orangey insects on the leaf buds. Are those tiny insects the culprits (and what are they?) Or is it my watering methods? I water once a day because I planted it in my perennials bed, but I was told it was too much -- that oleander likes dry conditions.
- G. S., Madera, CA
A. Plants under stress seem to attract insect pests and I suspect a colony of aphids or mites are attacking the new growth on your oleander. I doubt they are the cause of the browning, curling leaves, however. Oleander thrives when given full sunshine and little water. Since you water every day, I suspect your plant is getting far too much water, which is stressful at best, and could lead to root rot disease. The browning leaves might even be a symptom of too much water coupled with general transplanting stress. Try to reduce the amount of water your oleander gets, moving it to a drier location if necessary. Hose the insect pests off the plant and inspect it frequently, washing off any new pest populations. Once your plant regains its health, insects shouldn't find it nearly so attractive.
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Q. About 4 weeks ago I purchased 2 different clematis vines from a department store, each with a 5-inch stem. I planted them immediately in what I thought were ideal conditions -- cool soil with morning sun. I kept them both watered. The green leaves have died and I don't see any new signs of life. Are they dead? What did I do wrong?
- K. M., Pearisburg, VA
A. If there are no signs of green sprouts coming from the stems or soil, I'm afraid they're probably not going to make it. It's hard to say exactly what went wrong. The plants may have been stressed by conditions at the department store when you purchased them, and the additional stress of planting was too much for them. You might contact the store to see if they offer any guarantees. It's also possible that you planted them too shallowly. Potted plants should be set in the soil at the same level they were growing in the container. However, bare-root plants (which are usually sold with the roots surrounded by moist sawdust or peat moss) should be planted deeper, with the root ball set 3 to 6 inches below the surface of the soil -- which in your case means burying part of the green stem. Deep planting helps keep roots cool and moist. If you want to experiment, you can dig up the roots and, if you see any signs of life, replant them slightly deeper.
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Q. I planted 10 daylily plants this spring and half are already blooming. However, some of the leaves are turning brown. Is this due to a disease starting, or weather, or bugs, or what? Also, how long do the blooms live and do you pinch them off after they close?
- R. W., Lancaster, NY
A. "There are several foliar problems, such as leaf streak and russet spot, that may affect daylilies. Usually these problems are not serious, and they can be controlled easily by removing infected leaves as they occur. Be sure to clean up all foliage in the fall to help keep any disease spores from wintering over. Sometimes a damp season or overhead watering can make the problem worse, particularly with leaf streak. In addition, some varieties seem to be more susceptible than others.
The blooms last only one day (hence the name) and can be removed by snapping them off daily as they fade. The main stem can be removed by cutting near the base once all the buds on it have bloomed. This helps the plant conserve energy by preventing seed formation, and is a good idea for the first season. After that, although not strictly necessary, it does help keep the plants looking tidy."
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Q. Two weeks ago I put in a new flower bed with a red crape myrtle and two fountain grass plants, plus some annuals. Since they are new, none of them really look great yet, but my crepe myrtle looks the worst. The leaves are turning yellow at the bottom and falling off, and it looks like it's wilting. I added commercial potting soil at planting time. Do you know what is wrong?
- M. W., Yukon, OK
A. Based on your description I would suspect the plant is undergoing transplant stress. Make sure the soil is kept evenly moist but not sopping wet, and that the potting soil immediately around the roots is being watered adequately. Sometimes potting soil will dry out faster than the native soil and this can cause water stress. Keep in mind that overwatering can be as detrimental as under watering. Also look at the foliage carefully for signs of insect problems and/or fungal problems.
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