How to treat plum tree fungus

Plum Tree Diseases - What to Watch for and How to Protect Your Plum Tree

Our trees form such important parts of our yards and home gardens. They give us privacy from neighbors, shade to make our yards tolerable on hot summer days, and sometimes even tasty fresh fruit. In this article, we will identify plum tree diseases, treatment options, and, of course, prevention of the diseases .

Plum Tree Diseases: Bacterial

Bacterial canker (

Pseudomonas syringae)

Bacterial canker is easiest to spot in the spring when buds do not open and the nearby twigs die back. Cankers also occur and trunks and main branches and manifest as oozing spots, or sores, that produce a sour smell. The cankers additionally create spots on leaves that begins as small purple spots that transitions to black before finally turning into a shot hole as the leaf tissue dies and falls out.

Ultimately, the canker causes necrosis of the leaves and woody tissues until the branch, and perhaps the whole tree, dies.

photo shows gummosis, a bacterial canker causes decline of fruit trees
Source and Treatment of Bacterial Canker

Bacterial canker affects all stone fruit trees and colonizes on the surface of healthy trees. It only becomes a problem for stressed trees or trees with an entry point of leaf scars or pruning wounds.

Unfortunately, treatment for bacterial canker is disappointingly inconsistent and ineffective. Some options are to apply a copper fungicide or a broad-system fungicide. In addition to trying a fungicide, containment will be your most important course of action as it can be spread from tree-to-tree.

Bacterial Spot (

Xanthomonas campestris)

Bacterial spot also produces oozing cankers on the tree trunk, sometimes so significantly that the tree is left pitted and ridged from the ever-increasing cankers. Long before you notice the cankers, the bacterial spot will damage the leaves.

You will see angular, as opposed to round, spots on the underside of the leaves. Shot holes will appear. And then finally, the leaves will turn yellow and fall off the tree, which will then lead to sunburned fruit. Fruit may also have black sunken spot.

Sunken canker on trunk of tree, a common symptom of bacterial
Source and Treatment of Bacterial Spot

Bacteria colonizes on healthy tree tissue then spreads with rain to the leaves, fruit, and twigs. Warm rain and temperatures above 65 degrees Fahrenheit permit the bacterial growth, so warm, wet springs year after year promote severe infections.

The oozing cankers can also spread the disease to uninfected trees.

Chemical applications can prevent additional or new infections but cannot cure an existing infection. Prevention will again be key.

Crown Gall (

Agrobacterium tumefaciens)

Crown Gall creates burly gnarls on the root or trunk of trees, and it impacts many, many types of fruit and nut trees. On plum trees, the gnarls will be soft and sometimes hollow. The galls stunt the growth on young trees and can cause wood rot on older trees.

Tree Burr Knot (Burl) or Crown Gall close-up, plant disease that cause abnormal growths of galls
Source and Treatment of Crown Gall

Crown Gall is a bacterial, and it is particularly problematic because it can live independently in soil and in roots. This means that even if you get rid of a diseased tree, the crown gall can remain.

There are no effective treatments for Crown Gall, but botanists suggest just tolerating it for the life of the tree. Trees can continue to bear fruit.

Plum Tree Diseases: Oomecyte

Phytophthora Root and Crown Rot (

Phytophthora spp.)

Root and crown rot is caused by Oomecytes, which are water molds. Plum tree leaves will have noticeable maladies – wilting, followed by discoloration and then premature drop. As the disease progresses, you will see branch and twig dieback. Brown lesions encircle feeder roots, and the feeder roots eventually disappear. Ones left behind will be woody and brittle. The tree may ooze black sap.

Root and crown disease can stunt growth, and eventually cause the death of the tree. Young trees are most susceptible.

Source and Treatment of Root and Crown Rot

Root and crown rot can survive in the soil for years, but it requires a high level of moisture to infect a tree. Gardeners are most likely to have the disease introduced to their property by the planting of an infected tree purchased elsewhere. It can then spread through the soil.

Phosphonates can help control the rot. Ensure your soil has proper drainage.

Plum Tree Diseases: Fungal

Armillaria Root Rot (

Armillaria mellea)

Armillaria root rot is commonly known as oak root fungus and is ultimately fatal to infected frees. The soil-borne fungus infects the root and crown of the plum tree, and by the time you can see above-ground symptoms, it is likely too late to save the tree.

During wet seasons, mushrooms may appear at the base of the tree, but the small stand of mushrooms is a deceptive sign of the massive infection below the ground.

Source and Treatment of Root and Crown Rot

Containment of infected soil, wood, and root tissue is critical for preventing the spread of the fungus. The fungus continues to live in the dead root tissue long after the tree is cut down or dies back. Planting a new susceptible tree in the same soil is not recommended unless there is complete removal of the tree and and fumigation of the soil.

Black Knot (

Apiosporina morbosa)Closeup of a fungus growth on a tree branch

Black knot is a blissfully accurate and descriptive name for fungal diseases. On plum trees, you will see black, swollen masses on the twigs and branches. The masses will start as subtle green or light brown soft spots that grow over multiple seasons to black tumor-like growths. They can be up to a foot long and encircle an entire branch.

When the branch is encircled by the knot, the branch will die. The tree may suffer from decreased fruit production, structural damage, and ultimately death if the infection is severe. Mature trees are more resilient and may survive without any noticeable ill effects.

Source and Treatment of Black Knot

The knots house the fungus, and the fungus spreads throughout the tree and even to other trees by spores that settle on new green growth. Without moisture, the spores will not develop into a larger colony that creates the knot.

Unfortunately, fungicides alone will not remedy black knot, and removal is much more laborious. Botanists recommend pruning the tree in the winter to remove any visible knots. Remember, the spores will be released from those knots in spring. Applying a copper fungicide can help prevent the creation and spread of the stores.

Dip your shears in a 10% bleach mixture between cuts, and burn the infected branches. As it takes a few seasons for the knot to materialize, it may take a few years of heavy winter pruning to fully control the infection.

Brown Rot (

Monolinia spp.)Plum Fruit Infected by Fungal Disease Monilia cinerea in Orchard.

Brown rot impacts stone fruit like plum trees the world over, but it will actually be most noticeable as fruit rot rather than abnormal tree growth. Like black rot, brown rot is a fungus spread by springtime spores. The fungus overwinters in infected fruit and twigs and then settles on the blossoms in spring after being transported by wind and rain.

The fruits develop brow spots that expand into larger spots or rings of spores. The fruit rots and shrivels, known as a mummy.

Cankers will also appear on the twigs and branches, creating cankers that can disrupt the vascular system in the tree and cause damage or death.

Rotten mummified plums on the fruit tree, Monilia laxa (Monilinia laxa) infestation, plant disease
Source and Treatment of Brown Rot

Because the spores overwinter in the infected fruit and twigs, you must be sure to clear infected fruit as it appears and at the end of the growing season. Prune the infected twigs and branches to remove the source of the infection, and treat with a fungicide.

Apply a fungicide during bloom and prior to harvest for maximum effect

Powdery Mildew (Sphaerotheca pannosa and Podosphaera tridactyla)Powdery mildew on leaf of apple tree

These two fungi manifest as a white, powdery substance that rapidly spreads throughout the tree. Sphaerotheca pannosa effects the fruit while Podosphaera tridactyla attacks the leaves. Depending on which type, it may look stringy or like a powder.

Source and Treatment of Powdery Mildew

The spores overwinter on fallen leaves, bark, and on shoots of the tree. The powdery mildew easily spreads from roses and other stone fruit trees, so any treatment must treat the collective impacted plants. Apply fungicide starting at full bloom at 10-14 day intervals until fruit pits harden. Rotate fungicides to prevent resistance.

Rust (

Tranzschelia discolor)Plum rust (Tranzschelia pruni-spinosae) on green leaf of Plum or Prunus domestica

Plum rust creates tiny, rust-colored spores on plum tree (and other fruit tree)leaves. It can cause leaf drop and a reduced plum yield, but it is unlikely to kill the tree. Plum trees are usually impacted at the end of the growing season, making it more resistant to the mal effects of the fungus.

Source and Treatment of Plum Rust

The spores spread easily on the wind, but the fugus can be treated with fungicides. Rotate your chemicals to manage any resistant fungi.

Plum Tree Diseases: Viral

Plum Pox Virus

Virus-triggered symptoms of chlorotic mottling and mosaic on green leaves of bird cherry.

The USDA identifies plum pox virus (PPV) as a serious viral disease impacting plum and other fruit trees. Fortunately, it does not kill the tree, but it does reduce the fruit yields of impacted trees and it mottles and severely deforms the fruit, rendering it unmarketable. PPV does not cause harm to humans, but it can devastate commercial orchards.

Source and Treatment of Plum Pox Virus

PPV is highly contagious and is spread by the infected plant or fruit.

Once an infection is identified, the source tree and all trees within a 50-meter radius should be removed and destroyed.

Plum Tree Disease Prevention

Because many of the above diseases are easily or effectively healed, prevention will be the best bet to maintain the beauty, fruit production, and ultimate survival of your plum trees. Here are some key tips to avoid infection of your plum trees

Beautiful ripe purple plum on a branch in autumn
  • Correct pruning is the number one thing you can do to keep your trees safe. Prune flowering trees when they are blooming because wounds heal the fastest. By eliminating weak, damaged, or brittle branches, you are removing possible entry points into the tree. The increased air circulation promotes a dryer environment to impede fungal growth
  • Apply sealant to any wounds to prevent diseases from entering the tree, and not jus pruning cuts. Did you nick the tree with the weed whacker? Did your teenager tie a hammock and cause a break in the bark? Seal it.
  • Select disease-resistant varieties. Many species of plums are resistant to some diseases but not others. Consider the most pressing risks in your climate, and be sure to choose a strain that is resistant to that issue.
  • Apply NEEM oil to fungus-infected trees. NEEM oil is a natural infection control medium that smothers insects and spores alike. For trees struggling with a fungicide-resistant fungus, the NEEM oil can inhibit the spread of spores and give you a leg-up in controlling the fungus through pruning and condition control.

Excited for more plum content? Then check out our plum trees page for the latest growing tips, care guides, recipes, and more!

Black Knot Disease: Symptoms, Treatment and Control

Best product
for Black Knot

Black knot is a widespread fungal disease that attacks plum and cherry trees, both fruiting and ornamental. The fungus, Apiosporina morbosa, (also identified as Dibotryon morbosum and Plowrightia morbsum), singles out trees of the genus prunus, which includes peach, apricot, and chokecherry. Once established, black knot is easily identified with its hard, uneven, black galls that seem to enwrap twigs and branches. Black knot is a slow developer, taking a season before it’s visually apparent and producing spores. The trick to controlling the fungus is identifying the infection well-before the disease becomes firmly established. If left to grow, it effectively strangles new growth, girdling branches and dooming the tree to deterioration and poor fruit production. Insects and plant diseases use the galls as an entry to the tree.

The disease cycle starts when spores are released from established knots where the fungus overwinters. This occurs during damp spring conditions when temperatures reach 60 degrees or higher. The spores travel to other parts of the tree and, depending on the breezes, to nearby host trees. The spores germinate on stems beneath a thin film of moisture, often at the juncture of a new leaf start. They form small, olive-colored swellings over the first season, darkening in color as the season progresses, hidden by the leaves they’ll eventually kill,. By the second year, the galls are expanding quickly, especially where the weather remains humid. The growing infection begins releasing its own spores as it swells into the dark, easy-to-spot (especially after leaves have fallen) warty black fungus that coils along stems and branches. At this point, astute pruning and chemical treatments may not be enough to save the tree, no matter how careful the pruner is not to spread spores or leave them behind when removing the galls.

Paying close attention to your fruit trees and catching the infections as soon as they’re apparent, followed by quick pruning and careful disposal of the gall-infected branches, can save trees. Organic treatments can also help protect trees while keeping harmful chemicals off your fruit.

When choosing new plantings, consider that some varieties of tree and shrubs are more susceptible to the disease than others. They should be avoided in areas where the fungus is prolific. Tart cherry varieties are said to be less susceptible to the disease than sweet. Japanese plums are said to be less susceptible than American varieties. A number of plums, including President, Early Italian, Santa Rosa and Shiro carry varying degrees of resistance to the fungus. Susceptibility varies depending on the climate zones. Varieties that are susceptible in humid southern climates may be less so in dryer or cooler ones. Talk to your local nursery staff to see which varieties of plums, cherries, and ornamentals do best in your area. The Ohio State University Extension site has a chart on their black knot page that list the various levels for susceptibility to a number of plum and cherry tree varieties. (Not surprisingly, plum trees with resistance to black knot don’t do well in cold, northern climates.)

How to Control

  • Inspect your trees carefully for first signs of the disease. This is best done in winter, when leaves are absent, but should be continued as well throughout the growing season. Look for cracks, discoloration, swelling, or other first signs of infection. Check carefully around twig and leaf axils.
  • Remove any knots that are found. This is best done during winter when spore production is down. Cut well-past the galls, four to eight inches, to ensure all the infection and its spores are removed. Larger branches with established knots should be removed entirely. Use a pruning knife or chisel to remove galls on trunks and large branches, cutting down to the wood and out to at least an inch beyond the infection.
  • Continue to inspect for and remove galls as the season progresses.
  • Take care not to spread spores when pruning trees with black knot. Don’t allow twigs or other cuttings to fall to the ground where the spores could survive.
  • Dispose of infected stems and branches by burying or, where allowed, burning. Small cuttings can be stuffed in trash bags and hauled away. Do not compost any infected cuttings unless your heap has an internal temperature of 160 degrees (not many do).
  • Clean pruning tools as you use them with a solution of 1/2 cup bleach to a gallon of water. Wipe tools between cuts and leave your pruning blades in the solution for three to six minutes when finished. Or use a safe, commercial fungicide cleaner such as Physan 20.
  • The Alberta Ministry of Agriculture and Forestry has a detailed guide to pruning and disposing of infected trimmings at their website.
  • Fungicides can offer significant protection against black knot, but are unlikely to be effective if pruning and sanitation are ignored. Organic gardeners will want to avoid all but OMRI listed fungicides.
  • Spraying trees with NEEM oil, a natural fungicide that controls leaf spot, rust, scab, and other tree fungus, can help inhibit the spread of black knot (it will not kill fungus that is already present). Spray trees per instructions just ahead of leaf and blossom emergence and, if possible, ahead of rain. Continue on a 7-10-day cycle until weather dries. Use of other fungicides can also discourage spores from germination. But few are specifically indicated for use on already infected trees.
  • Spraying lime sulfur on trees during the dormant period is said to prevent the production of spores. Copper sprays applied during dormancy may also inhibit spore production.
  • Take out wild cherry and plum trees around your property. They harbor the disease and release spores that are easily carried to your susceptible nursery trees.
  • When planting new trees, place them away and upwind from established or wild prune and cherry trees.

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Diseases of plums – we treat the fungus and recognize the virus + video

Wounds on the leaves and gum on the fruits – what is happening?

It happens that oval spots of gray-brown color with a crimson edge 4-5 mm in size appear on the leaf plates, which dry up and fall out after a couple of weeks, and through holes form in their place. These signs indicate the development of a fungal disease called clasterosporiasis or perforated spotting. With a large scale of damage, the leaves dry out ahead of time and fall off.

Gum on fruits

Fruits are often affected. On them you can see small depressed spots, where growths form over time, from which gum protrudes. With the further development of the disease, the plum is affected to the very bone, is significantly deformed, stops growing and dries up.

In advanced cases, entire branches are affected. Elongated spots form on the bark, they burst, and gum oozes from the cracks. Neglect of treatment leads to the death of entire groups of shoots and bacterial cancer. The spores of this fungus overwinter in the leaves, so clean up fallen leaves regularly and don't leave them to decompose until next year. Remove affected shoots promptly in early spring and autumn after harvest, do not overcrowd plantings, clean wounds in case of gum formation and treat them with garden pitch.

Use 1% solution of Bordeaux liquid or copper oxychloride to control perforated spotting. We carry out the first spraying in early spring before bud break and after the appearance of the first buds. Then we repeat the procedure immediately after flowering and again after 2-2 weeks. The last spraying should be no later than three weeks before harvest. If klesterosporiosis has affected the stone fruit culture too much, additionally spray the tree with a more concentrated 3% solution of Bordeaux mixture after the final collection of all fruits.

Gum disease – how to avoid the “bitter tears” of a tree?

Gum disease is a common problem in stone fruits, including plums. It appears as a thick mass, the color of which varies from light yellow to brown. In appearance, the gum resembles a hardened resin. It is formed in the most vulnerable parts of the cortex. Mechanical damage, inaccurate pruning of branches, lack of sealing with garden pitch, sunburn and adverse weather conditions - all this leads to cracking of the bark and the formation of wounds that gum fills over time.

Gum treatment

Excessive watering and oversaturation of the crop with mineral fertilizers, especially nitrogen, can provoke the development of gum. Damp and cold weather, numerous damage to the bark by pests are another faithful companions of gum treatment. Gum is a good platform for the development of bacteria, stem cancer and the death of the tree as a whole.

To prevent gum bleeding, regularly monitor the condition of the bark, do not allow the formation of cracks and wounds on it. In case of gum formation, remove it with a sterile garden knife, clean the place to living tissue, disinfect with a 1% solution of copper sulfate and carefully seal it with petrolatum or garden pitch. Remove severely affected branches.

Rust, coccomycosis and black fungus - a triple attack on the leaves

Brown spots that are localized near the veins of the leaf blades indicate infection of the plum with a fungal disease - rust. The main peak of the disease occurs in July. If the tree is left untreated, then small brown swellings will appear on the outside of the leaf, which over time can occupy the entire area of ​​\u200b\u200bthe leaves. Trees affected by rust are weakened due to premature fall of leaves and a decrease in immunity. Rust is caused by a fungus. Therefore, in order to avoid infection, remove fallen leaves in time, and also treat trees with fungicides. Before flowering, spray the horticultural crop with copper chloride and 1% solution of Bordeaux liquid after harvest. Attention, three weeks before harvesting the fruits, we stop all spraying.

Sooty fungus

Dangerous and very common plum disease - coccomycosis. The main focus of its defeat is the deciduous part of the tree, although the fungus can also affect young shoots and fruits. The activity of coccomycosis occurs in the first half of July. The first signs of damage - the formation of multi-colored spots on the leaves, from purple-violet to red-brown. With a prolonged course of the disease, small spots grow and cover almost the entire surface of the leaf plates, and a pink-whitish bloom appears from the inside of the leaf. These are fungal spores. These leaves dry up and fall off.

If the fungus infects the fruits, they become covered with watery spots, stop growing and dry out. Favorable conditions for coccomycosis are warm, humid weather. However, the spores of the fungus perfectly tolerate cold and frost, settling in fallen leaves, so it must be removed and burned for the winter. We fight coccomycosis using standard familiar methods: we spray the trees before flowering and after harvesting with a 1% solution of Bordeaux mixture or copper oxychloride, using 30–40 g of the substance per 10 liters of water to prepare a solution.

Is there an unpleasant black coating on the leaves and shoots? This is a clear sign of soot fungus. It prevents the penetration of oxygen and sunlight into the tissues of the plant, thereby slowing down growth and disrupting the normal vital activity of the culture. Whatever the cause of the soot fungus, reduce watering and reduce planting density. As the main control measure, use spraying with a copper-soap solution, at the rate of 5 g of copper sulfate and 150 g of laundry or green soap per 10 liters of water.

Monilial burn - how to deal with a dangerous fungus?

If the branches of plum trees dry, become covered with brown spots, this is a sign of a fungal disease - moniliosis. This disease appears in cold and wet weather in the spring, when the flowering of trees begins. The flowers are the first to fall into the lesion, then the leaves and branches dry. Over time, spores form on them, from which the bark becomes covered with gray growths. Affects monoliosis and fruits. Wet weather is ideal conditions for the development of the fungus in fruits.


Plums with mechanical damage and cracks are the first to be affected. Penetrating into them, the fungus forms brown spots, they increase in size and merge. At the final stages of the lesion, the spores of the fungus form small gray-brown growths on the drain. This is one of the most dangerous fungal diseases. If measures are not taken to treat it, infected trees can completely die.

The fight against moniliosis begins with the collection of affected fruits located on the tree and under it. We must burn all collected specimens; they are not suitable for compost. After harvesting, we spray the trees with a 1% solution of copper, iron sulfate or Bordeaux mixture.

Plum pockets - causes and manifestations of the disease

Deformed plums are not uncommon in the garden. However, if the fruits on your trees form elongated and do not have a distinct shape, these are clear signs of plum pockets or marsupial disease. In such infected specimens, there are no seeds, the taste of the fruit is lost. Another characteristic sign of a fungal infection is the formation of a sticky powdery coating with spores. You can track the infection of stone fruit crops with marsupial disease immediately after the start of flowering. As with many fungal diseases, the ideal conditions for the development of plum pockets are high temperature and high humidity. The fungus overwinters in the scales of the buds and forms mycelium on the shoots.

Plum pockets

If you do not start the fight against marsupial disease, you can lose up to 60% of the crop. To prevent this from happening, remove the branches that are dry and damaged by the fungus, and burn the affected fruits. In early spring, before bud break, treat the trees with a 3% solution of Bordeaux liquid, and immediately after flowering begins with a 1% solution of the same preparation. In order for the chemical preparation to linger in the tissues of the plant, and not to be washed off during the first precipitation, use systemic fungicides, such as Horus, before and after flowering.

Viral infections - a global threat to the plum crop

If fungal diseases are easy enough to treat, then the same cannot be said about viruses. One of the dangerous viruses is plum dwarfism. Its initial signs can be seen in small leaves, they have an elongated shape and uneven edges. Over time, the compaction of the sheet plate and its fragility are added to the non-standard form. A large number of such leaves are located at the top of the shoots. The flowers of stone fruit crops are tied poorly, have a painful and pale appearance. As a result, the dwarfism virus leads to slow growth and death.

Fighting the virus is useless. Dig up the infected tree and burn it. As a preventive measure against dwarfism, we recommend using only sterile garden tools, using all pest control methods on the site, and choosing virus-resistant seedlings.

Smallpox occurs not only in humans, but also in stone fruit crops. Smallpox, also known as Sharkey's virus, primarily infects leaves, forming chlorotic ring spots on them, which can be clearly seen in sunlight. The fruits are also susceptible to infection. They become dense, significantly deformed. Inside, the pulp acquires a brown-red hue, and ring depressed spots form on the skin, gum is visible in the cracks. Such fruits lose their taste, they fall off and are absolutely not suitable for human consumption.

Plum virus infections

To prevent the development of Sharkey virus, choose resistant varieties such as Renklod, avoid planting Mirabell Wangangheim, Nancy and Zimmer. The disease can manifest itself on stone fruits throughout Russia, it is especially common in the southern regions, where all favorable conditions are created for its development. Aphids are frequent carriers of Sharka, so be especially attentive to this pest and take appropriate measures to destroy it in time. Ornamental plants should not be planted near plums, as well as those crops that can be potential carriers of the virus - clover, sweet clover, nightshade, etc. Infected specimens are not subject to treatment, they are uprooted and burned.

Chlorotic ringspot is another dangerous plum virus. It is characterized by the formation of a blurry pattern on the leaf plates. Over time, the annular spots fall out, and in their place there is a thin mosaic border and through holes. The virus also affects the leaves. They become smaller, become narrow and rigid, have a wrinkled texture. Infection can occur through non-sterile equipment, poor-quality planting material, and also be carried by pests. Affected trees must be dug up and burned.

Witch's broom - what does it have to do with mystical inventory?

Witch's broom is a fungal disease that affects stone fruits, especially plums. Affected branches become thin, close to each other, there are no flowers on them, and leaves are rarely found, which are significantly deformed and small. Outwardly, the overall picture really resembles a panicle, from which the disease probably got its name. Over time, a whitish coating (spores) can be seen on the underside of the leaf plates, from which they become even more fragile and wrinkled. The pale shade of the leaves often changes to red.

Witch's broom

The proven method of spraying trees with a 3% solution of Bordeaux mixture in early spring, as well as a less concentrated 1% solution of the drug after flowering, helps to prevent the development of the disease. Among other fungicides, Ridomil Gold has a good effect against the fungus, which should be applied a few days before flowering, as well as Thiovit Jet after flowering.

  • Author: Ole Lukovoe