How to deal with black spot leaf disease

How to deal with black spot leaf disease

Black spot is a fungal disease (Diplocarpon rosae) that affects roses. The fungus develops as black spots on the leaves, which eventually causes the leaves to turn yellow and drop off. Besides looking unsightly, it can seriously weaken the rose plant. Black spot thrives during cool, moist weather, while extreme summer heat limits the disease.

How to deal with black spot leaf disease

What Does Black Spot Do?

Black spot will look like somewhat circular black spots on leaves. It usually occurs on the upper sides of leaves, but can also develop on the undersides. The outer margins of the black circles are ragged or feathery and they are usually surrounded by a ring of yellow.

Spots typically begin on the lower leaves and move upward. They can appear as early as when the leaves first unfurl. These spots can enlarge and eventually merge. Affected leaves often fall off the plants, and if left unchecked, the entire plant can defoliate.

The fungus can also infect young canes, causing dark purple or black blisters on the canes, and even the flowers may show some red spotting. Infected plants will set fewer flower buds and without leaves, the plants become stressed and susceptible to more problems.

How to deal with black spot leaf disease

Environmental Controls for the Problem

While there is no cure for infected leaves, black spot can be prevented. Existing spores overwinter on infected fallen leaves and stems, waiting for favorable conditions. The spores germinate in spring and are disseminated by water splashing onto the plant. Spores must be continuously wet for 7 hours before infection occurs. The spores develop fruiting bodies, called acervuli, in the black lesions. These produce spores that splash onto new tissue, spreading the disease.

Give the Plant Ideal Growing Conditions

True for avoiding any plant disease, a healthy, vigorous plant is less susceptible to problems. Roses prefer a sunny location with well-draining soil and regular, weekly watering. Plant roses in a place where they receive morning sun, which helps dry moisture from the leaves. Full, all-day sun is best.

Good Air Flow

Provide good air circulation around and through your rose plants. Do not plant your roses too close to other plants. Prune to open the spaces between canes, if the plant gets too dense and air cannot get through. By providing good air circulation and ensuring canes don’t cross, black spot will have a harder time spreading.

Proper Watering

Avoid getting the leaves wet while watering. There is not much you can do about rain, but avoid overhead sprinklers and focus water directly to the plant's roots.

Pruning

Remove any infected leaves and always do a thorough cleanup each fall. Remove and dispose of any remaining leaves when you do your dormant rose pruning in late winter/early spring. Spores can remain on leaves and stems and can reinfect whenever conditions are favorable. Within 10 days of the first symptoms, the disease has already started spreading. Spores spread by water. Prune out any canes showing signs of infection. Prune 6 to 8 inches below the infection and only prune in dry weather. Disinfect your pruners with a 10 percent bleach solution or alcohol between cuts. Dispose of infected leaves and canes—do not compost them, as the spores can reinfect plants. Make sure to clean up fallen leaves as well, and dispose of them properly.

How to deal with black spot leaf disease

Mulch

Apply a thick layer of mulch around the plants. Mulch prevents soil from splashing up on the plant, and if the spores are present in the soil, it will help prevent the spread of the fungus.

Topical Sprays for Treatment and Prevention

There are commercial and homemade, DIY-solutions you can use to try to prevent the spread of black spot. The treatment may seem time-consuming; it is a pesky problem. And, if after you have treated the plant, the black spots reoccur, you may need to spray your plants weekly starting in early spring.

    : Dissolve 1 teaspoon baking soda in 1 quart of warm water. Add up to 1 teaspoon of liquid soap. Spray leaves thoroughly. This mixture works as a preventive. It also offers some protection from powdery mildew.
  • Bordeaux mix: This is a fungicide that contains copper sulfate and hydrated lime. It can be used as a powder or mixed with water and sprayed. Bordeaux mix also repels some insect pests, but it can burn plant leaves. It is generally used as a preventative in the spring before plants leaf out.
  • Insecticidal soaps with added fungicide: You can use an organic fungicide, which is often sulfur added to regular insecticidal soap. The soap coats the leaves and helps the fungicide adhere to the plant.
  • Neem oil: Neem is an organic fungicide and pesticide, derived from the seeds of the neem tree. It gets inside the plant’s system, so you do not need to worry about coating everything or reapplying after rain. However, it can burn plant leaves in the hot sun. You should not apply neem oil within two weeks of using a product containing sulfur.
  • Sulfur: Sulfur prevents fungus diseases. It is also used to control several insect pests. Sulfur comes as a finely ground powder. If you prefer to spray it on, look for one that is labeled as wettable so that it will mix with water.

How to deal with black spot leaf disease

Warning

Sulfur can be mildly toxic to humans and other animals. You should wear protective clothing when you spray it. It can also corrode metal, so use a plastic sprayer. And it can burn plants leaves in hot weather.

Plant-Resistant Cultivars

Roses are often labeled for resistance, from highly resistant on down. If you are looking into black spot-resistance, you might as well look for a rose that is also resistant to rust fungus and powdery mildew. Rugosas, a newer shrub and ground cover rose, and many of the Canadian Explorer series roses like ‘John Cabot’ and ‘William Baffin’, show good resistance.

How to deal with black spot leaf disease

A common rose disease is known as black spot (Diplocarpon rosae). The name is very appropriate, as this fungal disease forms black spots all over the foliage of rose bushes. If left unchecked, it can cause a rose bush to totally defoliate. Let’s look at what causes black spots on rose bush leaves and steps for treating black spot roses.

What Causes Black Spots on Rose Bush Leaves?

Many frustrated gardeners wonder, “What causes black spots on rose bush leaves?” Black spot and roses usually go hand in hand. In fact, many roses get a little black spot, which can even be tolerated to some degree without any harm to plants. However, heavy infections can seriously defoliate plants.

Rose black spot is caused by fungus. Dark-brown to black leaf spots develop on the upper leaves, which eventually become yellow and drop. Black spot can be distinguished from other leaf spot diseases by its fringed edges and dark black color. Raised, reddish-purple spots may also appear on rose canes. Warm, humid conditions favor its germination and growth.

How to Control Black Spot on Roses

Once your rose bush gets attacked by the black spot fungus, its markings are there to stay until the marked leaves fall off and a new leaf is generated. The fungus that causes the black spots can be killed and not do any further damage to the foliage but the marks will remain for some time. In my rose beds, a rose named Angel Face (floribunda) was a black spot magnet! If I did not spray her when her leaves first started to form in early spring, she would most certainly get black spot.

My fungicidal spraying program for the last several years to prevent black spot in roses has been as follows:

In the early spring when the leaf buds on the rose bushes first start to push out the little leaves, I spray all the rose bushes with a black spot treatment fungicide called Banner Maxx or a product called Honor Guard (a generic form of Banner Maxx). After three weeks and then at three-week intervals, all rose bushes are sprayed with a product called Green Cure until the last spraying of the season. The last spraying of the season is done with Banner Maxx or Honor Guard again.

Should the dreaded roses black spot get ahead of you in the rose beds, a product called Mancozeb fungicide will stop black spot on rose bushes in its tracks. I found out about this great product a few years ago when rose black spot got ahead of me and the rose Angel Face was well under attack. The Mancozeb does leave a yellowish powder on all of the foliage, but that is part of how it works. This product is applied every 7 to 10 days for three sprayings. After the third spraying, the normal spraying program may continue. The black spot fungus should be dead, but remember the black spots on the rose leaves will not disappear.

The Mancozeb product may be mixed with another fungicide called Immunox and then applied to the rose bushes to lessen the amount of yellowish powder left on the foliage. Both are added to the spray tank as if they were the only product in the tank mix. I have personally used both of these application methods and both worked very well.

Preventing Black Spot on Rose Bushes

Treating black spot roses begins with prevention. Black spot rose disease control includes adequate planting sites, the use of resistant cultivars, and pruning. Roses should be planted in areas with plenty of sunlight and good circulation.

Good garden hygiene is important for treating black spot roses. During the growing season, overhead watering should be avoided. Removal of leaf litter and pruning of diseased canes (back to healthy wood) is also important. Keeping the rose bushes thinned well at pruning and deadheading times will help the airflow through the bush, thus also helping to prevent black spot on roses and other fungal disease outbreaks.

With any of the fungal diseases, an ounce of prevention truly is worth a pound or more of cure! Either having a routine spraying program or keeping a close eye on your rose bushes is a priority. The sooner roses black spot treatment starts, the easier it is to gain control of it. I like to use the Green Cure as my main fungicidal spraying product, as it is earth-friendly and does the job it needs to do. Neem oil can also be used, which helps control many rose pests as well.

Some people also use baking soda, which helps change the pH level on leaf surfaces, making it more difficult for black spot to infect plants. To make this organic solution, mix a couple of tablespoons (29.5 mL.) of baking soda with a gallon (4 L.) of water. Adding a drop or two of bleach-free dish soap will help keep the baking soda on the leaf. Spray both sides of the foliage. Reapply weekly and repeat after any rain.

How to deal with black spot leaf disease

Photinia shrubs sometimes contract a disease called Photinia leaf spot or Photinia black spot. Leaves are dotted with black spots that slowly spread until leaves wilt and fall off.

Little spots similar to tar spots appear on leaves. This disease is rarely deadly, although it does lessen the beauty of your Photinia.

Read on to learn about how to treat the disease and what causes it.

  • Read also:black spot disease

Treating Photinia leaf spot disease

Protecting photinia from leaf spot

  • Anti-fungal spray such as Bordeaux mixture is one of the best ways to prevent Photinia from falling sick.
  • It’s also possible to prepare your own natural fungicide from weeds and plants that might grow in your garden.
  • Spray at the end of winter or at the very beginning of spring.
  • Don’t spray if temperatures are below freezing.
  • Rake up or collect any leaves that are infected instead of leaving them near the shrub. Destroy them either by burning them or thorough composting.

Since the fungus spreads through splashing water from shrub to shrub, you can prevent photinia leaf spot if you :

  • Plant different varieties near each other in a mixed hedge, instead of only planting Photinia.
  • Alternate Photinia with other evergreen hedge shrubs
  • Prune your photinia as a standalone into a tree shape, to avoid low-lying leaves.
  • Water only near the ground, without splashing the leaves.
  • Avoid pruning in summer, because this would trigger new growth that the fungus will quickly colonize.

How to treat photinia leaf spot

Once leaf spot disease has appeared:

  • You should pick all infected leaves by pruning them out.
  • Diligently disinfect your pruning shears, scissors or secateur with methylated spirits or alcohol between cuts.
  • Spray at two week intervals, preferably just after a rain or shower.
  • Spray again with Bordeaux mix in fall.

What causes Photinia leaf spot?

How to deal with black spot leaf disease

A fungus called Entomosporium maculatum is what causes leaf spot on photinia. It is a microscopic fungus that overwinters on twigs and leaves that have fallen on the ground.

Symptoms of Photinia Entomosporium leaf spot

  • It starts off by creating spots of light swelling on leaves and then the color changes to brown and dark red, and ultimately to black or gray.
  • Young leaves and growth are the most affected.
  • In severe cases, spots grow until the entire leaf is weakened and falls off. Sometimes this happens before the leaf is even fully mature (still red).
  • First signs of infection appear near the ground on the lower levels of the tree.
  • Usually only leaves are affected, but sometimes buds and green shoots show signs of infection, too.
  • If untreated and conditions are suitable to the fungus, the photinia may die.

What conditions trigger photinia leaf spot?

  • Moisture, as for all fungus, is the main driver for photinia leaf spot.
  • Cool temperatures speed the spread of the disease (but it’s dormant when freezing).
  • Growing photinia close together also makes the fungus spread quickly.
  • Water splashing spreads the fungus spores (like seeds) from leaf to leaf.
  • Branches and leafage that hover near the ground are particularly prone to leaf spot, such as in hedges.

From all the photinia species, one of the most vulnerable varieties is the “Red tip” Photinia x Fraseri.

Entomosporium leaf spot is usually harmless in most climates, especially where summers are hot and dry. However, in moist climates with very wet spring and fall seasons, it may prove fatal to your photinia hedge.

Photinia leaf spot spread and contamination

Photinia is a wonderful hedge shrub and it’s often grown as a hedge. When leaf spot appears, it’s time to check for alternatives that may also bring joy without the hassle of dealing with the disease.

Can Photinia leaf spot spread to other trees and shrubs?

This particular strand of leaf spot, Entomosporium, can directly infect other members of the Rosaceae family such as:

What shrubs similar to Photinia resist leaf spot?

A favorite shrub that resists leaf spot is holly, as does its North-American endemic counterpart yaupon.

With unremarkable flowers but beautiful silvery leaves, silverberry also fills the spot… without leaf spots!

Spotted laurel is also beautiful, with built-in yellow spots on its evergreen leaves that don’t endanger the plant as a fungus would.

  • Also:Black spot disease in shrubs and garden trees

Smart tip about Photinia leaf spot

If you’re preparing cuttings from your favorite photinia, try to collect cuttings from specimens that aren’t infected to make sure the disease isn’t propagated, too.

Credits for images shared to Nature & Garden (all edits by Gaspard Lorthiois):
Red photinia leaf spot by John Vangelis under © CC BY-SA 3.0
Green photinia leaf spot by Krzysztof Ziarnek under © CC BY-SA 4.0

How to deal with black spot leaf disease

Many ornamental and edible plants display dark, necrotic looking spots on their leaves. This is a symptom of bacterial leaf spot disease. Bacterial leaf spot on plants will discolor, and in extreme cases, kill leaves. Tiny, microscopic, single celled organisms are what causes bacterial leaf spot. There are several methods on how to treat bacterial leaf spot and save your plant’s glorious leaves. Early identification is crucial to effective management of bacterial leaf spot disease.

Symptoms of Bacterial Leaf Spot

Bacterial leaf spot on plants may manifest in several different ways. Symptoms of bacterial leaf spot may include black edged lesions, brown spots with yellow halos, or just light and dark areas on the foliage. Spots are irregular and measure between 3/16 and ½ inch (5 mm. to 1 cm.) wide. They can occur on the top or bottom of a leaf and kill sections of the tissue when they cluster together.

Symptoms of bacterial leaf spot may also appear on the edges of a leaf, where it appears brownish yellow and the tissue dries and breaks off. The leaves become quite papery and delicate when the bacterial disease attacks the leaf edges. The disease is most prevalent on older leaves, but will quickly establish on newer tissue.

What Causes Bacterial Leaf Spot?

Organisms that cannot be seen with the naked eye are the cause of this visibly damaging plant disease. Wet, cool conditions promote the formation of these bacteria, which can spread on plants quickly. The bacteria splash onto leaves or overwinter on plant debris in soil.

Bacteria divide to reproduce and one bacterium can multiply quickly in just a matter of hours. Bacteria reproduce the fastest when temperatures are 77 to 86 degrees F. (25-30 C.). High rates of infection will cause leaf loss and can seriously compromise a plant’s health. This makes the disease extremely contagious and bacterial leaf spot disease treatment extremely important.

The pathogen is carried in infected seed as well, although, there are some disease resistant seed strains for food crops. Additionally, choose disease free transplants, rotate crops, and avoid overhead watering to prevent spreading the bacteria.

How to Treat Bacterial Leaf Spot

In addition to the previous tips on preventing the spread of the disease, you can use a copper fungicide on crops. This has limited management use unless it is applied early in the disease cycle.

On ornamental plants, remove the affected leaves at the first sign to prevent the bacteria from jumping onto adjacent leaves. Some of the most common hosts are lettuce, beets, eggplant, peppers, and large leaved ornamental plants, such as philodendrons.

Remove old vegetable debris in the garden and do not plant new crops where host plants were once growing. There are no recognized chemical treatments for bacterial leaf spot disease. Your best bet is prevention and mechanical control at the first sign of symptoms of bacterial leaf spot.

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Even the most conscientious and hardworking gardener is likely to encounter leaf spot problems on trees and shrubs. The seemingly sudden appearance of brown or black blotches on leaves and defoliation are common occurrences. It is unlikely that most homeowners will make it through a season without at least one problem with a leaf spot pathogen.

How to deal with black spot leaf disease
Rose Downy Mildew image by Joan Allen

Symptoms of leaf spots vary depending upon the causal agent. Although leaf spots can be caused by air pollutants, insects and bacteria et al., most are a result of infection by pathogenic fungi. Once into the leaf, the fungi continue to grow and leaf tissue is destroyed. Resulting spots vary in size from that of a pinhead to spots that encompass the entire leaf. Dead areas on the leaves are usually brown, black, tan or reddish in color. Occasionally the necrotic areas have a red or purple border. Partial to complete defoliation may occur under favorable conditions for the causal fungus.

Many of the leaf spot fungi have a similar life cycle. The causal fungus over-winters on fallen leaves. In the spring, during or following a rain, spores produced by the fungus are discharged and carried by the wind and splashing rain to newly emerging leaves. The spore germinates and penetrates these young tender leaves causing infection. In a few days to several weeks, depending on temperature, small spots appear on the leaves. As the fungus grows, the spots enlarge. The fungus in the spots may produce more spores. These spores are capable of causing secondary infections on other leaves.

In general, the leaf spot fungi are favored by cool, wet weather early in the growing season. Leaf spot diseases are seldom a problem following warm, dry weather in the spring.

How to deal with black spot leaf disease
Phyllosticta leaf spot of maple image by Joan Allen

All commonly grown trees and shrubs are subject to attack by one or more leaf infecting fungi. Although coniferous trees (needled evergreens) can be severely injured by leaf spot fungi, they are rarely attacked in successive years. Therefore, control measures are rarely required. Many different fungi cause a variety of symptoms on hardwood trees and shrubs. Oak, maple, sycamore, ash, walnut, hickory and horse chestnut are some trees commonly attached by the anthracnose fungi. Anthracnose is caused by several species of closely related fungi that produce brown or black lesions on leaves. Distortion of the leaves and defoliation usually result. Another leaf spot fungus will often completely defoliate susceptible hawthorns such as Paul's scarlet and English varieties by midsummer. Leaf blister of oak is common following cool, wet spring weather. Many circular raised blisters are scattered over individual leaves. Although unsightly, there is little or no damage to affected trees. Symptoms of fungal leaf spots on elms vary from small, black, pinhead lesions to brown blotches covering an extensive portion of the leaf.

As many as ten different leaf spot fungi can be found on rhododendron. Although unsightly, they rarely cause serious injury. The above are a few of the hundreds of leaf spot problems likely to be observed by the home gardener.

In many cases, the home gardener becomes overly alarmed when encountering a severe leaf spot problem. A common reaction is to run for the sprayer and quickly apply a chemical to the ailing tree. Usually this is a waste of time and money. The majority of trees and shrubs have learned to live with leaf spot diseases. Even severe defoliation will not cause the death of an otherwise healthy tree. Also, by the time symptoms of leaf spot are obvious, it is often too late to apply a chemical for control. Trees, which are subject to serious injury when attacked by a leaf spot fungus, are those trees that are under stress. This might include recently transplanted trees, trees growing under droughty conditions or trees weakened by continuous insect attack. The additional stress of a leaf spot disease on an already weak tree may cause permanent injury or death. In such cases, chemical control of leaf spots is often recommended in the spring. In order to be effective, the proper fungicide must be applied as a protectant before the fungus spore is disseminated to the leaf. Most leaf spot fungi infect trees early in the spring just as the leaves are unfolding.

Successful control usually requires two to three spray applications. In general, the first spray is applied at bud break and the second seven to fourteen days after that. A third spray might be necessary, particularly during rainy periods. The more rain the more frequent the spray applications must be. Since many of the leaf spot fungi over-winter on fallen leaves, one cultural method of reducing the severity of leaf spots is to rake and remove from your yard all old leaves under the tree. This will reduce the number of fungal spores available to infect developing leaves in the spring. Disposing of old leaves is not likely to be effective if leaves from the same species of tree or shrub in your area are not disposed because spores of most of the causal fungi can be wind disseminated for long distances.

Despite good cultural practices, pests and diseases at times may appear. Chemical control should be used only after all other methods have failed.

For fungicide and pesticide information or other questions please call toll free: 877-486-6271.

Of all the problems that plague a garden, soil-borne pathogens are the worst. Here’s what to do when a fungus wrecks your plants.

How to deal with black spot leaf disease

Fungal Leaf Spot

Leaf spots originate with bacteria or fungus, both of which reside in soil or on nearby plants. Read on to find out what to do when a fungus takes over your garden.

Photo by: Julie Martens Forney

Julie Martens Forney

Leaf spots originate with bacteria or fungus, both of which reside in soil or on nearby plants. Read on to find out what to do when a fungus takes over your garden.

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Gah! Your garden has a fungus. Some microscopic, plant-killing pathogen has infected the soil, and now your tomatoes are stunted and yellowing, your onions are rotting at the ground and your pepper plants are laying on the ground with black spots on their dying leaves. So much for that garden-fresh salsa.

Soil-borne diseases like fungus are one of the most frustrating things a gardener can deal with because you don’t know it’s there until it makes your plant sick. And once you realize there’s fungus in your soil, it’s not easy to get rid of it. Soil-born diseases can live in your soil for a long time, waiting for you to put a plant in the ground. Once you do, the pathogen hops aboard that hapless host plant and spreads through your garden like wildfire.

What Is Fungus in Garden Soil?

Fungus exists naturally in soil, and most of it’s beneficial for your plants. But there are 8,000 varieties that have no purpose other than messing up your garden plants. They spread sickness like root rot that infects plant roots and keeps them from drawing water and nutrients into the plant. Stem, collar and crown rots hit the plant at ground level, where it touches the soil. Then there’s good old wilt disease that, no matter how much water you give your plants, leaves them as droopy as one of those melted clocks in a Dali painting. Damping off disease slays seedlings, causing them to die suddenly just after they germinate.

If you’re not sure what sort of fungus is messing with your garden soil, take a sample into your local Extension office for a free soil test. The local office is part of the Cooperative Extension System, a nationwide network of universities and federal, state and local governments that collaborate to teach you to be a better gardener, among other things.

CORVALLIS, Ore. – Do new buds and branches on your lilac look blackish, like they’ve been scorched by a blowtorch? Your bush might have a bacterial plant disease called lilac blight.

A cool, wet, rainy, spring season favors development of lilac blight, especially if rains follow a late frost or winter injury. Oregon State University Extension plant pathologists are warning that this might be a favorable year for the disease.

Actually known to plant pathologists by the complete name of “lilac bacterial blight,” this disease is caused by a bacterium Pseudomonas syringae pv. Syringae. The same organism is the source of bacterial blight on pear, blueberry, cherry, maple, and many other woody plants and the symptoms of lilac blight are similar in appearance to fire blight in fruit trees.

At first, leaves look perfectly healthy and then a short time later they look as though someone has placed an open flame near them. The dark black streaks on one side of young shoots show the progression of the disease. The flowers will wilt and turn brown and unopened flower buds become blackened.

Do not fertilize late in the growing season. Do not over fertilize young plants.

Lilac blight is difficult to control and it is recommended that you buy blight-resistant varieties whenever you plant new lilacs.

It also helps to space and prune your lilac plants so they are not rubbing against each other and air can circulate freely between the plants. Do not fertilize late in the growing season. Do not over fertilize young plants because high nitrogen favors disease development, explained Melodie Putnam, OSU Extension plant pathologist.

If your lilac bush does have infection, prune and burn all infected parts as soon as you notice them. A spray of copper sulfate during the early spring each year should help prevent the problem before the buds begin to break.

It also helps to space and prune your lilac plants so they are not rubbing against each other and air can circulate freely between the plants.

Lilac blight bacteria over-winter on diseased twigs or on healthy wood. Factors that weaken or injure plants – wounds, frost damage, soil pH, poor or improper nutrition and infection by other pathogens – predispose them to the disease.

Sources of this disease can include old cankers, healthy buds, leaf surfaces and nearby weeds and grasses. Wind, rain, insects, tools and infected nursery stock spread the bacteria.

Some species of lilacs have shown resistance in western Washington including S. josikaea, S. Komarowii, S. microphylla, S. pekinensis, and S. reflexa. Most cultivars of S. vulgaris are susceptible, but some have been observed with less disease when planted in a garden; those include ‘Edith Cavell’, ‘Glory’, ‘Ludwig Spaeth’, and ‘Pink Elizabeth’. Note that ‘Ludwig Spaeth’ is highly susceptible under intense nursery production systems.

If your lilac bush does have infection, prune and burn all infected parts as soon as you notice them. Spray copper sulfate during the early spring.

The disease starts as brown spots on stems and leaves of young shoots as they develop in early spring. A yellow halo may also be around the spot. Spots become black and grow rapidly, especially during rainy periods. Further infectious development depends on the age of the part of the plant attacked.

On young stems, infection spreads around the stem and girdles it so the shoot bends over at the lesion and the parts above it wither and die. Infections on mature wood occur only on cherry trees, not on lilacs.

Young, infected leaves blacken rapidly starting near the margin and continuing in a wedge-shaped pattern down to the petiole. Eventually the entire leaf dies. On older leaves, spots enlarge slowly. Sometimes, several spots will run together, and the leaf may crinkle at the edge or along the mid-vein. Flower clusters also may be infected and rapidly blighted and blackened. Buds may fail to open or may turn black and die shortly after opening. Symptoms are similar to those of winter injury.

To see photos of this disease, visit OSU Extension’s PNW Plant Disease Management Handbook. The handbook also reiterates these cultural controls for treatment:

Hi Tui, I have a Garden Belle pear tree in a sunny sheltered spot in my garden. I planted it about 6 years ago. For the first time this year it has produced some pears, but the leaves have black spots on them. I don’t know what I should do. Should I spray? If so, what and when? Thanks.

This sounds like black spot, which is a a fungal disease that pears are susceptible too. Controlling the disease is to understand the lifecycle of it. Black spot lands on the leaf of the plant and if conditions are ideal (usually wet weather in spring) it will start multiplying. The leaf then drops on to the soil and the fungus is spread on to the surface of other leaves by rain splash or watering.

Protectant sprays such as a copper based spray and plant spraying oil are effective as clean up sprays through winter and into early spring. Your local garden centre or DIY store will be able to recommend a suitable spray. Also, clearing away infected leaf litter from around the tree and disposing of by burning, throwing in the rubbish and not composting will help prevent spread.

Pick off infected leaves as you see them, this is not always practical but it does help prevent the spread. Mulch around the tree to help conserve soil moisture and keep them actively growing. Apply Tui Organic Seaweed Plant Tonic directly to the soil or as a foliar spray. This strengthens the cell wall of the plant and helps it withstand pest and diseases. Water the tree regularly and feed every 3-4 months with Tui Enrich Fruit, Citrus, Tree & Shrub Controlled Release fertiliser.