Powdery Mildew on Lilac
Have you noticed that many lilac leaves at this time of year are more white than green? The whitish appearance is caused by the powdery mildew fungus. The white “powder” is composed of fungal structures (mycelium and spores).
White spots on leaves usually start to develop in mid-summer and enlarge as the summer progresses. By late summer or fall entire leaves may appear white. Also in the fall, tiny specs (cleistothecia) appear on leaves. These fungal structures are especially evident on lower leaf surfaces.
Powdery mildew is seldom serious, causing more of an aesthetic problem than harm to lilac plants. As with many diseases, the best way to control powdery mildew is to prevent its occurrence. Cultivars and varieties are available that have resistance to the disease. On established plantings, it is helpful to remove dead leaves in the fall. This will help reduce the amount overwintering fungal inoculum. Also, improve air circulation and sunlight as feasible. Dense, shady, and damp conditions favor disease development.
Because the disease is seldom serious, chemical control measures are not usually warranted. When used, fungicides (such Funginex, Cleary’s 3336, Strike, or Bayleton) need to be applied when the disease first appears and repeated according to the label.
This article originally appeared in the August 25, 1995 issue, p. 131.
Lilac leaves coated with powdery mildew. Source: glimpsesofglory-karen.blogspot.com
Question: I have lilacs and every year at the end of the summer leaves are coated with a whitish powder. What can I do to stop this?
Answer: Wear green-tinted sunglasses!
OK, that was a bit flippant, but … that’s pretty much what you should do!
Powdery Mildew Is…
It’s important to understand that this disease, called powdery mildew, is pretty much harmless to lilacs, especially when it appears at the end of the season, which is usually the case. It doesn’t weaken the shrubs in any substantial way nor does it keep the plants from blooming normally the following year.
Fruiting bodies of Erysiphe syringae seen under a microscope. Source: bladmineerders.nl
We call the disease powdery mildew because the foliage seems covered with a white powder, but in fact, it isn’t really powder: what you see are the fruiting bodies of a microscopic mushroom that has set up shop on the upper surface of the leaf. These bodies produce the spores that will eventually be carried by the wind to another lilac.
There are over 1000 species of powdery mildew fungus, but the two most commonly seen on lilacs are Erysiphe syringae (formerly Microsphaera syringae) and Phyllactinia syringae. They are specific to lilacs and a few close relatives (one variety of Erysiphe syringae will attack privets , for example), but won’t attack other plants, so you don’t have to worry that lilac powdery mildew will damage your other plantings.
On lilacs, as on many plants, powdery mildew is mainly a disease of senescence, that is, of aging. It mainly attacks the leaves towards the end of their useful period (end of August and September). That’s why it doesn’t really harm the shrub: by then, your lilac has already stored up its energy reserves for next year. So, it’s of little consequence other than visually. And I suspect no one else besides yourself would notice your lilacs are ill. From a distance, at least, they just seem to have a grayish cast that most people would mistake for their natural coloration. There are gray-leaved shrubs, after all.
Controlling Powdery Mildew on Lilacs
Actually, you don’t really have to treat powdery mildew on lilac, given its minimal effect on its host. At most, you could try to prevent it with the following actions:
- Choose a less susceptible variety. Powdery mildew is pretty much limited to the common lilac, also called French lilac (Syringa vulgaris). Most other commonly grown lilacs, such as S. meyeri, S. patula and S. x prestoniae, are rarely affected or, if they do catch it, the damage is extremely limited and scarcely noticeable. But not all common lilacs are sensitive to powdery mildew. Here are a few that are resistant to the disease and will be symptomless most years:
Syringa vulgaris‘ Katherine Havemeyer’Source: http://www.denmulderboomteelt.com
- Syringa vulgaris ‘Arch McKean’
- Syringa vulgaris ‘Avalanche’
- Syringa vulgaris ‘Charles Joly’
- Syringa vulgaris ‘Charm’
- Syringa vulgaris ‘Edith Cavell’
- Syringa vulgaris ‘Firmament’
- Syringa vulgaris ‘Henri Robert’
- Syringa vulgaris ‘Katherine Havemeyer’
- Syringa vulgaris ‘Ludwig Spaeth’
- Syringa vulgaris ‘Macrostachys’
- Syringa vulgaris ‘Madame Lemoine’
- Syringa vulgaris ‘Marie Finon’
- Syringa vulgaris ‘Marie Legraye’
- Syringa vulgaris ‘ Harry Bickle’
- Syringa vulgaris ‘Paul Thirion’
- Syringa vulgaris ‘President Lincoln’
- Syringa vulgaris ‘Primrose’
- Syringa vulgaris ‘Sensation’
- Syringa vulgaris ‘Silver King’
- Syringa vulgaris ‘Vestale’
- Give the shrub the best possible conditions, including full sun with plenty of space, good air circulation and well-drained soil, if possible slightly alkaline.
- Prune the shrub to improve air circulation.
- Water the soil at the base of the lilac during drought, because powdery mildew tends to settle on plants stressed by a lack of water.
- Spray the foliage weekly with plain water during hot, humid weather (when the disease usually starts), as this tends to wash the spores off the leaves before they start to germinate. Do this in the morning so that the foliage has time to dry out before dark, otherwise it can leave the shrub susceptible to other diseases.
- Avoid fertilizing lilacs, especially with lawn fertilizers, as nitrogen, especially, tends to stimulate fast but disease-sensitive growth. In any case, the lilacs are very comfortable with very ordinary soil fertility: they’re just not heavy feeders.
- Collect fallen leaves in the autumn and, if you use them as mulch or compost, avoid using the final product at the foot of the lilac, saving it for other plantings instead.
Horticultural oil. Source: www.amazon.com
- Spray the foliage monthly with horticultural oil (available in garden centers). Start after the flowers fade in late spring and continue until fall. A light coating of oil can help keep the spores from germinating. Note that spraying with oil will not eliminate powdery mildew once symptoms are visible: it must be used as a preventative. I consider this method to be one of last resort, reserved for lilacs that have repeatedly shown themselves to be susceptible to the disease in the past and that I have not yet got around to tearing out.
Or Do Nothing at All
Personally, the only actions I would take would be points 1 and 2: plant disease-resistant lilacs under appropriate conditions for their healthy growth. Otherwise, why fight a disease that doesn’t harm the health of its host and is not even very noticeable? This is one of those situations where you should simply apply the 15 pace rule: before treating, step back 15 paces. If you can’t see the problem at 15 paces, it’s not worth treating.
Benign neglect in the garden? Yep, I’m all for it!
Powdery mildew is a common lilac disease indicated by a grayish-white coating on the leaves.
Q: I have a lilac that is covered with some kind of white fungus. It looks like it’s been snowed on. I was going to take it out since I’ve only had one lilac bloom in 3 years. What’s wrong with it, and is there anything I can do?
A: That sounds like a case of powdery mildew, which is a very common fungal disease on lilacs.
Some types are more susceptible to it than others, and it’s worse some years than others depending on weather.
Powdery mildew thrives in high humidity and especially in damp, shaded spots and on plants that are dense (which makes it harder for the leaves to dry out after rain or in humid conditions).
The good news is that this disease seldom kills lilacs. However, it can weaken the plant, make it look ugly from mid-summer on, and lessen the bloom performance.
One thing I’d do first of all is thin out any overly dense growth. Remove up to one-third of the branches, starting with the oldest ones and ones that are coming out from the same area and sending shoots into one another.
The ideal time to do that is right after the plant flowers in late spring. If you do it now, over winter or in early spring, you’ll cut off the flower buds that already have formed. But since you’re not getting many/any flowers anyway, you could do your pruning over winter when the branches are easier to see.
You can also shorten the remaining branches during this pruning if the plant is getting too tall.
This kind of thinning not only aids air circulation, it helps to rejuvenate the plant by encouraging young shoots from around the base. It’s the 2- and 3-year-old branches that generally bloom best.
Lilacs usually bloom best in the long haul with rejuvenation pruning each spring. If you remove one-third of the oldest shoots each year and let an equal number of new shoots replace them, you’ll always have nothing but wood that’s no older than 3 years.
Another thing to consider is sunlight. Lilacs grow and flower best in full sun, so if yours is in too much shade, moving it to a brighter spot should help both with flowering and disease-fighting.
If a nearby tree is growing and creating more shade each year, you can counteract that by thinning out the tree branches and/or removing some of its lowest branches.
A good anti-disease care tip is removing as many of the lilac’s infected and fallen leaves as possible. That removes disease spores from the area that can overwinter and reinfect the plant next season.
Also avoid watering your lilac overhead, if you’ve been doing that. Water the ground, if necessary… never over the leaves.
You really shouldn’t have to spray for this since it’s typically not a plant-killing disease. But if all else fails and you really are fed up with the lack of blooms and ugly leaves, fungicide sprays can slow or prevent powdery mildew.
You have to apply the sprays early in the season or at the first sign of infection, then repeat the sprays every 14 days (or more) so long as disease conditions are ideal. Sulfur and neem oil are two organic fungicides, while triforine is an effective chemical fungicide against powdery mildew. Always follow label instructions for exact application details.
If you decide to yank your balky lilac, there are varieties that do a good job of naturally resisting powdery mildew.
‘Charles Joly,’ ‘Sensation’ and ‘President Lincoln’ are three old-fashioned French types that generally get high disease-resistant marks.
Dwarf Korean lilacs and some of the other new dwarf types are also mildew-resistant, including ‘Tinkerbelle,’ Bloomerang® and ‘Josee.’
Colorado State Extension has a good website paper that goes into more detail about dealing with powdery mildew.
Treating Common Lilac Problems: What To Do For Pests And Diseases Of Lilac
Shakespeare memorialized the sweet smell of the rose, but obviously he hadn’t so much as sniffed a lilac, the undisputed perfumed queen of the spring. These beautiful, hardy bushes are a great addition to your landscape because they tend to be easy to care for and the problems with lilac bushes are mostly minor. Even so, it’s best to be prepared if you have a run in with lilac pests and diseases, so we made up a list of common lilac problems you may encounter.
Common Diseases of Lilacs
Although lilacs are a hardy bunch, they can succumb to problems like any other landscape shrub. Be on the lookout for these diseases:
Bacterial blight – The bacteria Pseudomonas syringae causes early shoot and branch dieback, distorted leaves and leaf spots that start out olive green, but soon develop water soaked areas. Those spots turn brown with yellow margins and begin to die. Blossoms may become limp or turn brown suddenly. Pruning away the diseased material and thinning the inside of the shrub is the best way to control this disease, but if the infection is widespread, a copper fungicide will help kill it quickly.
Powdery mildew – Powdery mildew is probably the most common problem in lilacs. It’s caused by a variety of fungal pathogens that result in leaves with a powered appearance, either in tightly organized spots or spread across the surfaces. Increasing the air circulation around infected leaves is the best treatment, so make sure to thin your plants yearly.
Leaf spots – Leaf spots are another fungal problem caused by a variety of pathogens. When you see tan spots appear on your lilac leaves, with or without causing the leaves to fall, you’ve likely got one of the many leaf spot diseases on your hands. As with powdery mildew, this problem is a result of high local humidity, so thin that shrub and clean up all fallen debris to prevent future infections.
Common Lilac Pests
Lilacs attract just a few serious pests, most of the caterpillars and leaf miners that may visit aren’t anything to be worried about. However, if either of these pests appear, it’s time for action:
Scales – Scales can be difficult to detect, many species look like cottony or waxy growths on the stems and branches of landscape shrubs. If you lift their covers though, you’ll find very small, brightly colored insects underneath. Scales are best treated with repeated applications of neem oil, spaced seven to 14 days apart. When they’re clustered together in one section of the plant, pruning them out is an excellent option.
Borers – The larvae of the clearwing moth is a boring insect that prefers to feed on lilacs. These tiny caterpillars spend most of their lives inside the stems and branches of your plant, only emerging to mate. Effective management centers around keeping the lilac healthy and happy, since sick plants are much more likely to attract borers. They have a number of natural enemies that will pick them off when the lilac is stronger and less appealing.
Remedy for White Fungus on Lilac Bushes
When you grow lilacs in your landscape, the lavender blooms are often one of the highlights of the spring season. If you discover a white powdery fungus marring the surface of your lilac leaves as you are admiring the blooming lilacs, you probably react with horror and dismay. Take heart–the white powder you see is mildew and, while it is unsightly, it will not harm your lilac bushes. You can take steps to prevent and remedy white fungus on lilac bushes.
Provide water for lilacs only during periods of extreme and prolonged drought. If rain has been absent for several weeks, water the lilac bushes by directing the garden hose at the base of the lilac bushes. Never spray the leaves and foliage of a lilac bush with water because the moisture on the leaves can lead to fungus. Water the lilac shrubs until the soil around the bushes is moist and then stop. Do not water lilacs any more than this because this can lead to powdery mildew.
Fertilize the lilac bushes with the all-purpose fertilizer in early spring. Mix the fertilizer with water according to package recommendations for the size of your lilac bushes. Apply the fertilizer to the base of the shrubs. Fertilize the lilac shrubs one more time after the flowers fade. Do not fertilize the lilac shrubs any more than this because over-fertilization will lead to an overabundance of new foliage. This new foliage would be especially susceptible to fungus.
Prune lilac bushes immediately after the flowers fade in late spring. Prune out any diseased or dead branches before they show signs of fungus. Remove branches on the interior of the shrubs to increase the air ventilation inside the lilac shrubs. This will help to reduce chances of powdery mildew infecting your lilacs. If you find foliage that appears to have mildew, prune it out only if there is another reason to remove it (the branch is dead or rubbing on other branches). The mildew alone will not harm the lilac plant.
Spray a fungicide onto the foliage of the lilac shrub at the first indication of powdery mildew if you desire. Coat all surfaces of the plant (tops and bottoms of leaves). Repeat the fungicide application once per week during the remainder of the growing season to control powdery mildew.
Pests And Diseases Of Lilacs
Diseases are always harmful. When lilacs or Syringa shrubs are affected by diseases, it may cause the plants to stop blooming or reduce their number of flowers. In many cases, diseases occurring in the previous year may result in the destruction of the flower buds. In some instances, growers may take preventive or even curative measures. It has often been seen that the lilacs in dry gardens in rural areas are perfectly healthy, while many of those in major cities are vulnerable to a condition known as leaf-roll necrosis. Usually, lilacs grown in places having dry summers and chilly winters are mostly free from diseases compared to those grown in places where the summers are humid and winters are mild.
Like diseases, even problems caused by pests like scales and borers may cause the plants to bear fewer blooms. For instance, Syringa vulgaris or the common lilac as well as several of its cultivars are among the lilacs that are very vulnerable to pest invasions.
Lilac borers These are very niggling pests that are actually the larvae of a wasp-like moth called Podosesia syringae var. syringae, whose wings are semi-transparent and brownish. This pest lays large amounts of eggs in late spring. They usually lay their eggs on the stems of lilac shrubs and ash plants. While they are hatching, the larvae penetrate the branches and are nourished by the wood. Initially, these pests remain out of sight and one notices their presence for the first time when they find the entire leaves on a branch or stem turning yellow and wilting. This usually happens during the spring or towards the beginning of summer. Infestation by lilac borers may cause the bigger branches to become distended and eventually break.
If you take a closer look at such branches, you will notice tiny holes measuring roughly about the size of a pencil lead in diameter at a level of one or two feet (30 cm to 60 cm) higher than the ground. Just below it, you will notice some sawdust. In fact, these holes are actually exit paths of lilac borers and they suggest that the pests have already left, but still some others may be at work. These pests are very visible when you are pruning the plants. In fact, you may even find the borer tunnels breaking through the heartwood, especially of the older branches.
Precisely speaking, stresses as well as wounded plants are most common hunting grounds of lilac borers. They are also common on the bigger and older stems or branches, particularly on the common lilac (Syringa vulgaris). Several pesticides are available in the market to effectively deal with lilac borers. Lilac leaf miners Leaf miners are basically the larvae of a small moth species called Caloptilia syringella. These pests bore tunnels between the leaf layers, thereby giving a blotched appearance to the leaves during the start of summer. Subsequently, lilac leaf miners turn over the leaves and feed on them externally. Eventually, the color of the affected leaves become brown, thereby giving a burnt appearance to the entire plant. When the first sign of leaf miner assault becomes evident, you can soak the leaves with neem or a nicotine spray. However, when you notice the damage, it is already very late to take curative actions. Nevertheless, you should immediately remove the affected leaves and clear the area beneath the shrubs of all leaves and debris during the fall with a view to protect the plants from being infected again. In fact, the damage caused by lilac leaf miners is more aesthetic compared to physiological. S. vulgaris or the common lilac is most vulnerable to invasion by leaf miners. Mites Lilacs are often susceptible to the eriophyid mite (scientific name Aculus massalongoi). This pest creates a rust or silver color on lilac leaves and may sometimes result in leaf-rolling. Oyster shell scale These are very bizarre looking insects that appear as flat, oval-shaped and lifeless lumps. While shielding themselves under a wax-like coating and scales actually damage the plants by pulling out their fluids. These pests lay eggs on lilac shrub/ tree barks either during fall or in spring. These eggs are hatched later in spring. The young scales are mobile and have a light yellow or orange hue. They measure roughly 0.1 inch (2 mm) in length. The legs of these pests wither when they settle on a place to feed. When you are pruning the stems of lilacs, you may possibly notice that the stems have become roughened and have an unusual gray and dry appearance. When you take a closer look at the stems, you will notice minute bumps that can be skimmed using your fingernail or the pruning shears’ blade. Lepidosaphes ulmi This type of scale is known as the apple mussel scale and you can control their infestation on lilac plants by pruning the branches that have been infested heavily. In the next spring, you should apply a dormant-oil spray before the emergence of new leaves. You need to undertake this treatment prior to the bud break and essentially on an arid, sunlit, mild morning. In order to avoid harming the lilac plant, ensure that you do not apply the dormant-oil spray when the temperature is below 39°F (4°C) or 48 hours before or after a frost. Preferably, you should undertake the treatment on a calm morning when there no frost is anticipated that night and the atmospheric temperature is over 60°F (15°C).
You can also eliminate scale by painting the lilac branches with a solution of lime-sulfur using a paint brush. Alternatively, you can directly spray a soap water solution on the plants to kill scale. Add one teaspoon (5 ml) of any liquid dish soap that is additive free (such as Ivory) to one quart (1 liter) water and spray the solution on the plants. In fact, the soap water solution is most effectual when sprayed in the later part of spring or the beginning of summer – the time when these pests are in the crawler stage. Continue spraying the soap solution till the foliage seeps.
Blight Usually, you will notice the first symptoms related to bacterial blight (scientific name Pseudomonas syringae var. syringae) right in the start of the season – either when the weather is hot and humid or immediately after the spell. The beginning of this bacterial disease may often be remarkable. All of a sudden, the leaves start appearing as if they have been scorched all along their edges, and subsequently the stems become black. Bacterial blight may also result in formation of black spots confined by a pale circle on the leaves. When this disease affects plants, their flower clusters first wilt and eventually die. This bacterium also infects other plants including cherry, pear, maple and many varieties of ornamental plants.
There is a different kind of blight, which is attributed to a fungal infection. This disease is caused by Ascochyta syringae and the symptoms of this plant disease are same as those caused by bacterial blight. The disease starts from the soil and spreads up when the soil is damp during the start of spring. While these diseases do not essentially kill the plant, but they make the lilac appear unattractive and ugly. Moreover, these blights can also damage the new growth. These also affect the blooms adversely and the blooms may be lost in the year of the infection or the subsequent, subject to the time of the bacterial or fungal infection.
Usually, it is very difficult to control blights. In fact, plants that have been damaged in some way and the new growths are most vulnerable to these diseases. In order to reduce damage caused by frost keep the foliage dry, ensure that the plants are well ventilated. If it has been found that maximum damage caused by blights is in the low-lying areas – places where cold, moist air collects easily. If you notice blight soon after the plants are infected, cut down all the infected parts and remove them as soon as possibly so that they do not spread to the healthy areas. Moreover, you always need to sterilize the saw or pruning shears between cutting different parts by wiping their edges with Lysol, alcohol or a home-made solution of one part domestic bleach and 10 parts of water.
In the following year, spray the plants with a copper fungicide while the weather during spring is still warm – a favorable time for infections. Do not undertake heavy pruning or feed the plants with too much fertilizers, as these promote fast, but weak growth. It has been found that the common lilac (S. vulgaris) and other lilacs like S. x hyacinthiflora that bloom early are most vulnerable to blights. Compared to the doubles, the singles are more susceptible. Similarly, lilacs that bear purple, magenta and blue blooms are more vulnerable to blights compared to those that produce lilac hued flowers. In addition, lilac species like S. villosa and S. x prestoniae are very susceptible to these diseases. However, lilac species as well as cultivars that bloom late in the season are able to resist blights to some extent. Mycoplasma This prokaryotic microorganism causes a disease known as witches’-broom, which is widespread in large varieties of lilacs compared to the shrubs grown in the backyard. This disease is manifest in the form of a clump on very thick growth on any common lilac shrub or tree. This disease was noticed for the first time in 1951 and till date remains to be rather mysterious. However, scientists have come to know that a pathogen similar to viruses and called MLO (mollicutes or mycoplasma-like organisms) witches’-broom. It seems that, these microorganisms form colonies in the phloem (sap) and disturb the flow of the sap, thereby killing a new growth point. This, in turn, leads to thick growth of shoots on the side of the plant – generally in the lower part of the plant.
It has been found that S x. prestoniae and S. x josiflexa, lilacs that flower later in the season, are more vulnerable to this disease. Initially, the affected plant may appear unhealthy, its growth may be twiggy (fleshless) and it may produce unusual bloom out-of-season or have growth flushes. Eventually, the plant dies. Ash trees are affected by a comparable disease that is called ash yellows. This disease may also affect vigorous lilac plants and may also spread to ash trees possibly through an insect. In order to prevent the plants from being infected by this microorganism and also treating the affected plants, it is important to prune them with tools after sterilizing them properly. For instance, you may wipe or dip the blades of the pruning shears, knives and cutters in Lysol, alcohol or a home made sterilizing solution prepared by adding one part domestic bleach to 10 parts water before pruning or cutting a plant. As of now, there is no cure for this disease. As soon as you notice a plant affected by this disease, remove the plant and destroy it immediately. Powdery mildew This is a fungal plant disease caused by Microsphaera alni, M. syringae. This disease attacks lilacs when the atmospheric condition is warm and humid. Generally, this fungus first attacks the older leaves that are towards the plant’s base some time in July and then spreads all over the foliage between the period mid-August and October, when the leaves fall. First the leaves develop ugly white or pale gray blotches, which gradually change to yellowish and eventually the leaves drop from the branches. When this disease affects plants, the growth of new leaves is also stunted. In most cases, the harm done to the plant is more aesthetic compared to physical. This is because the plant looks ugly. On the other hand, the leaves generally drop off at a time when they have already accomplished their tasks.
In fact, you can provide the plants with best protection right at the time of planting them. Provide your favorite lilacs with total sunlight and proper ventilation. In addition, you should preferably select species and cultivars that are hardy. Water the plants deeply by supplying the water right on the ground and not the plant. Majority of the cultivars as well as hybrids of S. vulgaris or the common lilac are vulnerable to this disease. Lilacs that are worst affected by powdery mildew include “Henri Martin”, “Mrs. W. E. Marshall”, “Buffon”, and “Marlyensis”. In addition, the variety called S. x chinensis “Metensis” is also very vulnerable to this disease. If you notice a tendency of your lilacs being infected by Microsphaera alni, you should grow the plants at the back of perennially growing plants like lilies as well as ornamental grasses, whose height conceal the disfigurement of the lilacs. Some of the lilac species that possess the aptitude to resist this fungal disease include S. emodi, S. meyeri, S. x diversifolia, S. yunnanensis, and S. x persica. Virus Ring spot is a viral disease that causes yellow or target marks on lilac leaves, which drop from the plants untimely. Eventually, the affected plants die. Since there is no cure for this disease, you need to destroy the diseased plants. Wilt While lilacs are seldom affected by verticillium wilt, this disease may affect plants of this genus when they are growing in soils where people earlier grew potatoes, tomatoes or eggplants. When grown in such soils, lilacs will die sooner or later. Hence, you need to remove the plants to a suitable location before it is too late. In fact, it is difficult to control wilt. Therefore, decide on a suitable place before planting your favorite lilacs. Lilacs
Growing garden lilacs
Lilacs in containers
Renovating and moving lilacs
From Joan Sullivan – Oct-04-2016 I had something on my lilac tree bark that looked like white powder. After taking a photo and zooming in, I could see that it was not powder but millions of individual “scales”. It spread from one lilac tree (about 3 years old) to the one right beside it. After much research, I was able to identify it as White Prunicola Scale. It had overtaken the trunk and branches, and with no “sure cure or treatment” for this advanced stage, we felt it best to remove the trees.