Black spot on leaves

Black Spots on a Palm Tree

Thinkstock/Comstock/Getty Images

Palm trees often grow in areas where frequent rainfall, tropical storms, and high levels of humidity are the norm. But these environmental factors contribute to the development of diseases that produce black spots on the palm tree, often defoliating the leaves and — in extreme scenarios — killing the tree.

Graphiola Leaf Spot

Graphiola leaf spot, also commonly referred to as false smut, is brought on by a pathogen of the Graphiola species, and is most prevalent in palm trees planted in geographic locales where the humidity level is exceptionally high. The Sabal palmetto, Chinese fan palm, and Washington palm are among the species most frequently affected. The disease manifests on the leaves — fronds — of a palm in the form of tiny, black spots that possess the appearance of a wart.


These black spots appear on both sides of the leaves and — just like a wart — are sometimes accompanied by the sprouting of a small, hair-like structure from within the growth. Young fronds typically display no symptoms of the problem. The rate of infection from this disease can be minimized by allowing significant space between trees in order to promote good air circulation and thus a reduction in the level of humidity in the surrounding air.

Bud Rot

A number of fungal pathogens of the Phytophthora and Thielaviopsis species, in addition to bacterial pathogens, cause the disease referred to as bud rot. Symptoms display as black lesions on the buds and young leaves of a palm tree. Periods of extreme rain, especially tropical storms, heighten the likelihood of the development of bud rot, while bacterial bud rot usually comes to fruition when the bud has been injured by cold weather. Fronds will wilt and the infected area eventually appears and feels slimy to the touch.

Bud Rot Management

Mature leaves sickened by the disease still remain green for several months before dieing. In extreme cases, the entire tree may defoliate, leaving only the trunk remaining. Once bud rot attacks a palm tree, the recovery of the specimen is unlikely. The best preventative method is to avoid overhead irrigation and never apply water to the leaves directly. Palm trees that are infected with bud rot should be removed and destroyed to prevent the spread of the pathogen.

Why Do My Palm Tree’s Leaves Have White Spots?

You might love the frilly look of a fan palm tree, or maybe prefer the understated beauty of a pygmy date palm.

But whatever your style, one thing’s for sure: palm trees with discolored leaves aren’t so good-looking. When palm trees are affected by a pest or disease, their leaves can take on a couple of different colors. Here, let’s talk about white spots on palm tree leaves— what are they, and where’d they come from? Most importantly, do white spots mean your palm tree is dying?

Keep reading for a quick rundown on why palm leaves turn white and what you can do.

What are these white spots on my palm tree’s leaves?

There are two common reasons why palm leaves might be spotted white. You’ll want to take a close look at your tree to figure out what’s what.

Why your palm fronds have white spots

Some palm trees, such as Pygmy date palms, have waxy surfaces which appear as tiny white spots on the leaves. This is normal and is nothing to worry about.

More plump, white “spots” that are slightly raised point to a scale insect infestation. A common critter that attacks sago palms is the cycad scale. When lots of scale pests invade your palm, they make leaves look as if they’re covered in white spots. Plus, leaves will likely turn yellow or brown as the insects drain nutrients from the plant.

Is my palm tree dying?

A scale insect infestation can be serious. If these persistent pests stick around long enough, the plant can eventually die.

Unfortunately, once scale insects are on your tree, there’s no guarantee it can be saved. But, if you catch them early on and take action right away, there’s a chance you can eliminate scale insects.

Here’s what to do:

Consult with a Davey certified arborist to determine the best course of action. Many scale insects are difficult to control with horticultural oils and require special applications of systemic insecticides.

Plumeria leaf spot

Hello there!
Sorry to see your Plumeria is having some issues there. It looks like it could be a combination of problems.
Because of the frequency of rains this very well could be a fungal issue, that’s what I am guessing many of the brownish spots are. But it also appears to be a little chlorotic.
Could you answer some follow up questions?
Is the Plumeria getting sufficient sunlight? It would need at least 4 hours.
Does the pot it is in have drainage? is it sitting in a saucer of water? (Be sure it is well draining soil too 🙂
Have you fertilized it this season? With what? (If you have liquid seaweed go ahead and give it a dose of that; get it started on a healing process)
Have you seen any insects at all, any webbing? Do any other plants on patio have insects? (Inspect under the leaves and on the stems)
The good news is that this plant will certainly grow new leaves to replace these and there are certainly things to treat all of these issues.
Here is a website with some general care instructions.

I will wait to hear back from you so we can go from there.
Thanks for reaching out.

Why did the leaves on my Plumeria alba develop black spots and fall off?

Hot Network Questions

  • What should a pilot flying IFR in IMC and on final, do if the vacuum system fails?
  • Relicensing content under CC BY-SA
  • Trade off between number of constraints and bounds of a variable
  • Choosing my name for my first publication
  • What are the various ‘properties’ of a diode?
  • Demystifying Seirawan-Kasparov 1983 king and pawn endgame
  • Can I delay my turn to the end of a round, by not rolling for initiative?
  • Given a list of strings, find all elements which are still in the list when any character is deleted
  • Can early 2000 era frame use the latest group sets
  • How to replace the string
  • What is the meaning of “officially” here?
  • Can the Actor feat allow a character to effectively speak a language they don’t know?
  • Can we call forms like “Зин”, “Дим”, “мам”, “пап” vocative case?
  • Short story about intergalatic pizza delivery via time travel
  • How do I handle a “fake” co-author?
  • What is the polite way to tell taxi driver that he can stop here?
  • What is this star shape artifact in old cartoons?
  • Fundamentally, why do some nuclei emit ionizing radiation?
  • Why aren’t expander cycle engines used on lower stages?
  • What is this web on the surface of the Sun?
  • What does “gross of” mean?
  • What is the purpose of using 8.33 kHz instead of 25 kHz frequency spacing?
  • How can merging two sorted arrays of N items require at least 2N – 1 comparisons in every case?
  • Ubuntu 18.04: Is dynamic swap space sizing practical? Running out of memory crashed Ubuntu

more hot questions

UConn Home & Garden Education Center

Leaf Spot Disease of Trees and Shrubs

Printable PDF
Click on images to see larger view
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.

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.
Life Cycle
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.

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.

Revised by UConn Home and Garden Education Center 2016.
Issued in furtherance of Cooperative Extension work, Acts of May 8 and June 30, 1914, in cooperation with the U.S. Department of Agriculture, the Dean of the College, Cooperative Extension System, University of Connecticut, Storrs. The Connecticut Cooperative Extension System is an equal opportunity employer and program provider. To file a complaint of discrimination, write USDA, Director, Office of Civil Rights, Room 326-W, Whitten Building, Stop Code 9410, 1400 Independence Avenue, SW, Washington, DC 20250-9410 or call (202) 720-5964.

5. Pests and Diseases of Hibiscus by F.D. Hockings

Hibiscus are attacked by a number of pests and diseases. Some are not very important but others require treatment to prevent the leaves and flowers from being destroyed.

Correct diagnosis of problems is of utmost importance because fungicides are effective against fungal diseases only and pesticides are even more specific. Each pesticide is effective against only a particular class or group of pest. If you use the wrong chemical you are wasting your time and money and your plants will continue to be damaged.

Always read the label on garden chemicals. Be aware of what the actual chemical is (the active ingredient) and not just the trade name. Carefully follow the recommended dilution rate stated on the label; too weak may not control the problem and too strong may harm the plants or more importantly you. Metricated measuring receptacles are inexpensive, so do not guess quantities. Addition of a non ionic wetting agent such as Agral or X77 will improve the effectiveness of sprays, but thorough coverage of both sides of the leaves is the key to successful pest and disease control. Spray materials should be mixed fresh for each spraying operation; do not use solutions that have been mixed and left overnight. If the plants are drought affected or if the temperature at the time of spraying is too high (32°C or 90°F or higher) plants may be damaged by sprays. Water plants thoroughly a day or two before spraying and apply sprays in the early Chewing Pest morning or late afternoon.

Wettable powder forms of chemicals are safer for plants than emulsifiable concentrates and further more, two or three wettable powders may be mixed with relative safety. Malathion, Lannate and several systemic insecticides sometimes cause injury to hibiscus plants.

In general, plants that are grown in clean surroundings and are properly fertilised and regularly (but not too frequently) watered, are less likely to be attacked by diseases and pests.
The pests of hibiscus can mainly be grouped as chewers or suckers according to the way they feed. In addition, there are a few miscellaneous pests that damage plants in other ways.

Chewing Pests

These include caterpillars and grasshoppers. Caterpillars are the larval stage of moths and butterflies. They devour foliage, sometimes stripping a plant of all its leaves. The Heliothos grub and the cabbage looper (commonly called inch worm) are the most prevalent worm pests of hibiscus buds, flowers and foliage. The Heliothos grub is nearly 5 cm (2 in) long when full grown, yellowish, green, or brown or lengthwise light and dark stripes. It is usually found in the bud or flower. The cabbage looper is greenish, the body tapering to the head, with a thin white line along the body. It is more often found on the leaf.

Grasshoppers and katydids consume large quantities of foliage. Katydids are green and feed at night. Neither are found in great numbers. Control to eliminate immediately, before they become too numerous. They can frequently be removed by hand.
Sucking Pests

These include aphids, jassids or leaf hoppers, mealybugs, scale insects, bugs and mites. Their mouth parts limit their feeding to piercing the surface tissue of the plant and sucking the sap.

Mealybugs are important pests. They excrete honeydew which attracts ants and serves as a medium for the development of sooty mould. Mealybugs are soft bodied and scale like insects usually covered with powdery or cottony, wax like material. They are around 6 mm ( %4 in) long when mature and make cottony nests at twig joinings and under leaves.
Spider mites or red spiders are tiny, less than 0.5 mm (1/50 in) long, and one of the most common pests. They are found by checking the undersides of leaves with a magnifying glass. They may be tan, red or purple. They suck plant juices causing tiny white spots on the leaves. Control early before infestation is great with Kelthane.

Aphids or plant lice are small, soft bodied insects about the size of a pinhead which attack new growth, causing leaves to curl and blossoms to be malformed. They are green to brownish, with one type being black. Ladybugs and aphid lions are natural enemies of aphids.
Whiteflies are about the size of a gnat, and their young are circular, flat, almost translucent, and hard to detect.

Thrips are tiny, fast moving, yellow winged insects. They leave silvery patches on leaves and cause buds to drop. Close examination with a
magnifying glass is necessary to find them.
Stink bugs are 1 to 2.5 cm ( ½ – 1 in) long, of a variety of colours and markings. They suck sap from buds, leaves and stems. They leave an odour on plants.

Miscellaneous Pests
Various other pests also cause damage to hibiscus.

Snails and slugs are night feeders and injure plants, especially in damp, shady areas. Shiny trails may be seen, and snail baits should be applied when the pests are most active, e.g. dewey mornings or in wet weather.
Beetles are chewing, hard shelled insects. Some feed on leaves, others on flowers. Some feed at night and hide during the day, others feed during the day. Their larvae feed on roots and bore through stems and branches. Carbaryl will protect against many of them.
Leaf miners are small insects that feed between the upper and lower surfaces of the leaves. They leave distinctive trails on the leaves.

Cutworms are the immature stage of certain moths. Typically they stay in the soil during the day and feed at night at the base of tender plants. Some feed on buds and leaves. Carbaryl as a dust or spray in the late afternoon is effective.

Leaf tiers and leaf rollers are caterpillars which make `homes’ for themselves by rolling and tying foliage together with strands of silk. It is difficult to get insecticide into them, however dipel and carbaryl are good controlling agents.

Millipedes, pillbugs and sowbugs thrive in moist soil, attacking roots and sprouting seeds. Soil applications of Diazinon are suggested.

A number of fungal and viral diseases commonly infect hibiscus plants; in addition, physiological disorders also occur.

Fungal Diseases
Leaf spots: Several species of fungi may cause brown or black circular or irregular shaped spots on the leaves. Infected leaves should be removed and burnt and the plants sprayed with a fungicide such as Mancozeb (Dithane M45, Manzion, Manzate). Sooty mould is a black fungus on the upper surfaces of leaves, growing in the secretion of aphids, mealybugs, many scales, and immature whiteflies. The mould spoils the appearance of foliage but is not particularly injurious to the plant. Kill the insects and the problem will disappear. Oil emulsion or miscible oil sprays will loosen the mould and help clean up the plants. By spraying this material at about sundown, the dew helps to free the sooty mould from the leaf, and a forcible stream of water from a hose nozzle next morning before the sun dries the leaf will wash away 90 % of the sooty mould. A fungicide such as Mancozeb may also be used.

Ants are fond of the honeydew excreted by aphids and mealybugs, and they may protect and move these pests around from plant to plant. Chlordane and Baygon are effective controls directed to a broad area around the ant hills as well as in the centre of the hill.

Root rots and collar rots: Several species of fungi may cause soft rotting of roots and sometimes also stems. Infected plants will often wilt as though they are short of water. In general, root rots are associated with over wet conditions brought about by overwatering or poor drainage. Treatment involves watering less frequently and improvement of soil drainage as well as soil drenches with fungicides such as Terrazole (Terrazole WP) or Fongarid (Fongarid).
Viral Diseases
Plants infected with viral diseases may bear deformed or cupped leaves or leaves with mottle patterns. Infection may be carried by insects or on secateurs or by propagation of infected plants. These plants generally lack vigour. Leaf symptoms are more obvious at some times during the year than at other times. There is no cure or treatment.
Physiological Disorders
These disorders resemble the symptoms caused by a disease but are not associated with infection by a fungus, bacteria or virus. Physiological disorders are the result of some unsuitable factor in the growing conditions such as over fertilising, trace element deficiency, over or under watering, soil too acid or alkaline, position too hot or too shady etc.

Bud drop: This is one of the most common physiological disorders of hybrid hibiscus. The problem is more severe in some seasons than in others and some varieties are more severely and more regularly affected than others. Sometimes an improvement can be effected by shifting the plant to another part of the garden. Sometimes if a variety is severely and continually affected by bud drop, it is better removed and replaced with another variety. The most common causes of bud drop appear to be lack of food or lack of water. Excessive amounts of nitrogen, particularly when associated with foliar fertilisers, have been known to cause bud drop. Double flowered forms seem more affected than singles. Regular watering and fertilising is the best cure.

Yellow leaves: Hibiscus bushes naturally discard their old leaves several times a year. The larger older leaves on the bottom of the bush will turn bright yellow a few days before they drop. This is perfectly natural and should cause no concern, unless of course the yellowing and dropping continues up the stems to the top of the bush. If this happens it is usually caused by excessive fertiliser or moisture around the root zone. The yellowing is usually triggered off by an excessively hot day, cold snap, or by spraying with unsuitable insecticides such as Malathion or Lannate. A number of the systemic insecticides will also cause yellow leaves, and could lead to complete defoliation if used constantly. Worrying is of no help; if you are really concerned don’t look at your bushes for a couple of days, by then the leaves will have dropped and the plants be looking good again. Remember the old leaves must die for the new ones to take their place.
Spraying Safety Measures and Equipment

When spraying on a regular basis, it is advisable to cover every part of your body for self protection. Cover ails or overalls, boots or shoes, safety gloves, respirator and safety glasses are adequate protective apparel. Do not smoke while handling poisons or spraying. Shower well after spraying, and wash clothes separately from normal washing. Obtain a poison and antidote list from your Department of Agriculture or Primary Industries. It’s a must to have on hand. Make sure your spraying equipment is in good working order and condition at all times. Thoroughly wash the equipment after use so it is ready for next time.

Do not use your spraying equipment for any weedicides at all, particularly herbicides containing hormone 2 4 D and 2 4 5 T. Have a separate unit for this as these herbicides are particularly toxic to hibiscus and other plants, causing malformed leaves and flowers. It will take your plant a long time to get over this type of damage if it ever does. Remember when spraying with herbicides that any slight drift can cause severe damage, so keep well away from your precious hibiscus. Never use white oil sprays and fungicide sprays mixed together as this will have toxic effects. Always read the compatibility chart on the label before mixing two or more sprays together! Never use left over sprays that were pre mixed the day before. It is desirable not to pour excess sprays down drains where they can be washed into creeks, streams and rivers. Burying this waste is one safe method of disposal.

There are many different types of sprayers on the market, some are excellent products whilst others barely do the job for which they were intended. Choose a sprayer that will do the job for you with the least amount of effort. Remember hibiscus are reasonably large plants and require fairly frequent spraying and if this turns into a heavy chore or major operation then the task is more apt to be put off, resulting in more damage to your plants. A Big Boy spraying attachment which uses the pressure from your water supply is an easy method of applying sprays, particularly when there are plenty of large hibiscus bushes in the garden. It does use a little more spray but the savings in effort and time more than compensate for this. The Rega gen spray and uni spray are also ideal units. Their adjustable spraying heads make it easy to reach high branches. A little extra time spent in choosing the right sprayer for your needs will result in less time spent in spraying.
How and When to Spray
It is a fact of life that to obtain the best from hibiscus they must be sprayed at certain times of the year. Many people spray their hibiscus constantly and regularly to combat invasions of bugs, etc., and while this does keep the plants healthy, constant spraying can have a disastrous effect on other helpful insects in the garden, not to mention the birdlife.

When pests appear, the first thing to do is identify them. The next step is to select the right spray for that particular pest. In the past we had certain knockdown sprays that simply killed everything, poisoned the garden beds and would not break down for many years. These chlorinated hydrocarbons were accepted as the great breakthroughs in their time, saving people time and money by only spraying once. We know now that the war on pests is a constant one. Instead of killing off harmless predators by indiscriminate spraying, selecting the right spray for the right pest keeps the predators around to help us in the war against the pests.
Today there are many newer and better sprays on the market, and one of the great advantages of these new insecticides is that they break down rapidly. Hibiscus growers in the past encountered many problems from using systemic insecticides, and although a number of the new insecticides are still systemic they do not have the same damaging effect as the old types. It is alright to use systemics occasionally it is their constant and regular use that creates a problem.

Past experience tells us not to spray hibiscus regularly with the same insecticide. Always try to alternate your sprays, e.g. if you use endosulphan this week use diazinon the next time you spray, then change to carbaryl and so on.

While the best time for spraying is generally not during the heat of the day, for a bad infestation of hibiscus beetle the middle of the day is best. At this time the blooms are wide open and you can direct the spray onto the beetles it is just a waste of spray and energy if you do the spraying when the flowers are not fully open. If you have a problem with army worms or heliothos caterpillars, spraying toward evening is advised.

Always read the instructions on the label carefully; if in doubt ring your local nursery or Department of Agriculture for correct dilutions. Many insecticides have very small hard to read instructions (a good magnifying glass is handy for reading labels on bottles). A well defined medicine glass is also necessary for correct dilution rates. It is always a good idea to use a wetting agent when spraying as this helps the spray `stick’. White oil is good for this purpose; however, it is not recommended on hot days and never with fungicides.

Do not spray for the sake of spraying; sometimes only a couple of caterpillars are causing the damage and they can be picked off by hand. Aphids can often be hosed off, and snails captured by using an old terracotta drainpipe.

Do not put off spraying either. An infestation of beetle or army worm can gallop away and it will take a lot of spraying and a long time for the plants to recover. Look at your plants regularly; neglect is the biggest cause in the outbreak of insect pests. Remember also, healthy plants can repel insect pests better than unhealthy ones. Keeping your plants well watered and nourished keeps them free from pests and diseases as well.

Investing in a good sprayer is well worth a few dollars extra for the time saved. Learn to use it properly for each pest. Spray where the pests are, e.g. under leaves for loopers and aphids, in the flowers for beetles and caterpillars, around the base of plants for army worm. Do not be frightened to ask questions regarding the use of certain sprays on certain pests; most nurseries these days have good qualified staff who are only too happy to offer expert advice on insecticides and spraying.

Never mix insecticides together, even though many insecticides are compatible homemade ‘cocktails’ are definitely not the way to go. Mixing insecticides and fungicides together can be hazardous to hibiscus. Different plants are attacked by different pests there is no `wonder insecticide’ available to combat all the pests on all the different plants. Use the insecticide applicable to your problem and you will find better results obtained each time.

Excessive spraying is just as damaging as not spraying at all. Use the right insecticide and spray only when necessary. Read the instructions carefully and clean your equipment thoroughly after use. Encourage the predators who in turn will help keep a lot of pests down.

Recommended Fungicides

Not many fungicidal problems are encountered in growing hibiscus; however, an infection of Phytophthora or Pythium can be fatal. While there are fungicides to help combat these diseases, the control is often more expensive than replacing the plant with a new and healthy specimen. When a plant succumbs to these diseases it is good practice to remove the infected soil and replace it with fresh soil before replanting. Selecting plants that have been grafted onto good disease resistant rootstock, such as H. albolacinatus `Ruth Wilcox’, will ensure that the need to spray for such diseases is kept to a minimum. Culture that keeps the plants vigorous and healthy will aid in warding off many fungus diseases.

Black spot

Black spot, also spelled blackspot, common disease of a variety of plants caused by species of Pseudomonas bacteria or by any number of fungus species in the genera Asterina, Asterinella, Diplotheca, Glomerella, Gnomonia, Schizothyrium, Placosphaeria, and Stigmea. Infections occur during damp periods and appear as round to irregular black spots on leaves and sometimes on petioles, stems, and flower parts of susceptible plants.

Black spot on rose leavesW.H. Hodge

Black spot of roses is a serious widespread disease caused by the fungus Diplocarpon rosae. On rose plants, the spots are roundish and up to 1 cm (0.5 inch) in diameter with fringed margins. Leaves on susceptible varieties turn yellow and drop early. Affected plants may defoliate twice in a season, are greatly weakened, produce fewer and inferior blooms, and are subject to canker diseases and winterkill. Large numbers of spores are formed in speck-size fruiting structures (acervuli) and disseminated by splashing rain, dew, overhead sprinkling, and gardeners working among wet plants. The spores germinate and penetrate rose tissue in 9 to 18 hours or longer; new leaf spots appear in 3 to 16 days and spores in 10 to 18 days. The cycle may be repeated throughout the growing season. Black spot may be controlled by fungicide application, planting resistant varieties, and removing any infected leaves immediately.

Leaves and sometimes stems are marked by dark blotches caused by a fungus. The spores overwinter on fallen leaves, stem lesions and bud scales, and reinfect the plant the next spring when there’s a flush of new foliage. If these leaves are then infected, they too eventually turn yellow and drop. If not dealt with, the plant will weaken.


Rose black spot is very similar and can be dealt with in the same way.


Leaves are marked with purple or brownish-black spots, then turn yellow and fall. Smaller marks sometimes also blotch the stems. Plants can be weakened by regular attacks.

Find it on

shrubs, roses


Fallen, affected leaves must be promptly destroyed, along with any stems showing signs of infection. The best way to avoid the problem – which thrives in warm, wet conditions – is to lay a thick mulch around the plant. This helps lock moisture in the ground, and stops rain splashing the spores from the soil on to new growth.



Spray with a fungicide containing myclobutanil. Begin spraying each fortnight from early spring, just as the new foliage emerges, as a preventative measure.

Leave a Reply

Your email address will not be published. Required fields are marked *