Apricot Leucostoma Canker Info – Treating An Apricot With Leucostoma Canker

Apricot Leucostoma Canker Info – Treating An Apricot With Leucostoma Canker

Leucostoma canker generally isn’t a problem in healthy, actively growing apricot trees, but once infected, apricots with leucostoma canker are extremely difficult to control and can shorten tree life substantially. This stubborn disease, which also affects peaches, cherries, nectarines, and plums, is a serious problem worldwide, especially in cooler climates. Read on for more apricot leucostoma canker information.

What Causes Leucostoma in Apricots?

Leucostoma canker in apricots is caused by two related fungal pathogens: Leucostoma cinctum and Leucostoma persoonii. The pathogens invade the trees only through dead or wounded tissue, usually in late fall and early winter, or late winter and early spring.

The disease can enter the tree through scars or injuries on small twigs, and wounds on larger branches. The most common infection sites are insect injuries, pruning wounds, and bark and buds damaged or killed by winter cold. Damage by rodents and mechanical damage by equipment also creates an entryway for the disease.

Apricot Leucostoma Canker Symptoms

Diseased bark forms cankers and pimple-like growths that ooze copious amounts of amber gum. The cankers grow larger every year, gradually turning from dark brown to black, with a rotten smell. Usually, a callus forms around the damaged area, thus creating a protective wall. However, the canker may resume growth in late fall or early spring when the tree is dormant.

The affected bark shrinks from surrounding healthy bark, eventually drying out, cracking, and sloughing from the tree. Twigs and branches die when they are completely girdled by the cankers. Leaves turn yellow, wilt, and die.

Treating an Apricot with Leucostoma Canker

There are no fungicides currently registered for use against apricot leucostoma canker symptoms, and the disease is notoriously difficult to control. However, the following tips may help prevent the disease, or at least keep it in check.

Control pests, especially peach tree borer and oriental fruit moth, as the pests can do serious damage that allows the pathogen to enter.

Wrap trees with plastic guards to deter rodents but be sure to remove the guards during the summer.

Fertilize properly in early spring but avoid excessive fertilization. Avoid fertilizing late in the season, especially with high nitrogen fertilizers. Late fertilization results in succulent new growth that is highly susceptible to winter damage.

Mound soil against the base of the tree to drain water away from the trunk. The soil will also help prevent ice buildup and injury by cold temperatures.

Prune apricot trees correctly and at the proper time. Avoid severe pruning. Remove all damaged and dead growth. Burn it immediately to prevent the spread of pathogens.

Water properly, using practices that prevent run-off. Careful watering practices are critical in irrigated orchards.

Gummosis can be described as a situation in which there is a discharge of sap or gum from a tree. It is mostly associated with stone fruits, apricots, peaches, and plums.

This behavior in trees is caused by a number of factors which will be explained in the course of this read.

The most prevalent factor attributed to gummosis in trees is caused by a fungus known as Cytospora, now called Leucostoma.

Interestingly, gummosis can only infect vulnerable weakened trees which have been stressed over time resulting in wounds on the tree.

Also, cuts inflicted on trees as a result of pruning is another cause for gummosis infection. Natural factors like Sunscald and even extreme cold temperature can also provide an opportunity for gummosis infection on your tree.

The only way to prevent this infection is via prevention.


There are believed to be two species of Leucostoma that infects trees which are L. persoonii and L. cincta.

L. persoonii infection is mostly associated with stone fruits, apricots, plums, peaches, and cherries which are grown at a low elevation in warmer climates.

L.cincta on the other hand, is associated with apples and cherries grown at a high elevation in cooler areas.

The two species of fungus are known to be prevalent across the United States, throughout British Columbia and Ontario, Canada. Haven caused problems in states such as South America, Europe, and Japan.


Trees with symptoms of gummosis normally display signs of tree flagging looking worn out, and bearing a different texture and color from other parts of the tree.

The Leucostoma fungi leaves an imprint of a dark amber color on the part of the tree it infects. Once scrapped off, the phloem beneath the tree’s bark takes the color of cinnamon brown.

Normally, it is common to see the effect of gummosis on trees during the periods of winter and spring. However, the tree is able to fight back the infection when it starts growing again, but unable to do so in the fall. This effect on trees can be seen in periods when tree tissues take on a lighter or darker color.

In order to ascertain if the infection is caused by Leucostoma canker or other causes, a look at the tree’s fruiting bodies – identified where you can find protrusions on the surface of the tree’s tissues that takes the form of small black pimples.

The fruiting creates thousands of spores on the tree’s tissue, while those of L.persoonii can travel as high as 260 feet.


Haven being aware the opportunistic infection gummosis can only attack vulnerable and worn out trees, you should practice healthy mulching, water and nutrition.

Take steps to fertilizing with nitrogen during the periods of late winter or early spring. This should be done to prevent your tree from being vulnerable as a result of cold in the fall.


It is important to take utmost care when pruning so as to avoid cuts on your tree. You should not prune in wet or cold weather. While pruning, make proper cuts such as leaving stubs, flat cuts, and flush cuts will make your tree vulnerable to gummosis.

You can prune back to healthy wood by carefully taking out the infected limbs and twigs from off your tree. This should be done during periods of dry weather conditions so as to provide a conducive atmosphere for the wound to heal in quick time.

Also disinfect your tools between cuts with Lysol wipes or 10% bleach solution.

Note that in cases where there is extensive damage to your tree, it may not be possible to prune out all the parts that the fungus has spread to.


To prevent a gummosis infection as a result sunscald during winter, you can consider any of these two solutions:

The first is to paint your tree with half white latex and half water-based paint.

Your second choice is to apply white tree wrap on your trees from December to March.


You should take protective measures in treating rodents and insect attacks on your tree. Simply spray insecticides to keep off borers from boring holes on your tree.


This can be adopted as a preventive medium against gummosis infection to the base of your tree in cold weather conditions. All you need do is drain out water from the tree’s base.

If you reside in areas where there is a large concentration of this fungus, it is important to constantly treat your tree with chemicals that help prevent its attack.

Make use of captan, thiophanate-methyl, or lime sulfur (Bordeaux mixture) in 50% latex or kaolin clay to areas to freshly cut pruning wounds. Do not use copper hydroxide-based chemicals as it is toxic to trees.


Always endeavor to keep an eye on your trees to check if there are any parts with wounds or worn out.

It is common to find Leucostoma canker attacks in backyard trees, therefore great care should be taken while pruning to prevent cuts. However, if in the event of pruning you inflict cuts resulting in wounds on the tree, apply a chemical treatment. This will help prevent the fungus attack.

Keep a close watch for gummosis infection on your tree. Where you find any, determine if it was caused by fungal injury. When sure, take out the damaged tissue before it spreads by pruning back to healthy wood.

In the event you lose a tree to gummosis, completely take off such tree from the root to prevent it from spreading to other trees as the fungus have discovered to continue living on dead tissue.

If you have experienced and successfully treated a gummosis attack on your tree, let us know how you did it

2) Bacterial spot of peach and nectarine, Xanthomonas arboricola pv. pruni

Photo: Gerald Holmes, CA Polytechnic St. San Luis Obispo, Bugwood.org (left), Photo: Clemson Un. - USDA Coop. Extension Slide Series, Bugwood.org (right)

This is a difficult and expensive disease to control. Infections occur only when foliage and fruit are wet. Foliar lesions begin as small dark spots. In defense, the leaf quickly walls off the spot and drops the spotted area, leaving a shot-hole. Many infections can make leaves look tattered. Where infections occur on the midvein, leaves turn yellow and often defoliate. Fruit infections cause spotting and cracking of the fruit. The best approach is to choose varieties that are moderately to strongly resistant to this disease.

Philadelphia Orchard Project

We recently received an update from Penn State Extension about bacterial canker on stone fruits (cherry, plum, peach, etc.) which provides one upside to hot midsummer temperatures. According to their recommendations, “summer is the best time to prune your [effected] trees, particularly during dry weather. The bacteria do not like hot, dry conditions and the pathogen population will be at its lowest. Research out of Cornell showed no benefit of copper applications before and after pruning. Save copper sprays for the fall and early spring when cool, wet weather favor bacterial populations to grow and trees will be the most vulnerable.”

So, what is canker? I’ve done some more research and found online resources to help you out with explanation, identification, pruning, and management tips! When there’s no precipitation scheduled in the forecast and its been dry for a couple days, please get outside, monitor your trees, and water any young plants, get your emergency pruning done!

To ask more questions and learn more about pest and disease management of fruit trees, stay tuned in to POP’s upcoming events lists for Community Orchard Resilience Education (POPCORE) course updates and specific Pest and Disease Management Classes.

Latin names: Pseudomonas syringae and P. morsprunorum

Common names: gummosis, blossom blast, spur and twig blight, sour sap, and dieback

Latin names: Leucostoma persoonii and Leucostoma cinctum (teleomorph) and Cytospora leucostoma and Cytospora cincta (anamorphs)

Common names: perennial canker, peach canker, Valsa canker, and Leucostoma canker

Identification (plenty of photos below)

These infections are most noticeable when it looks like sap is oozing out of your tree in one or more places. This sap is, in fact, the pathogen surrounded by a sugary layer of protection, which can then be spread via water droplets carrying the bacteria or through fungal spores carried in wind and water.

Cankers don’t always have to be oozing, however. Older or dormant infections might appear as sunken areas on branches or trunk bark, dessicated (dry) and cracked areas, areas that look like the tree has tried to heal over old wounds, or areas that look scarred.

Fruiting buds, vegetative buds, flowers, leaves, and fruits can all be affected by these diseases and show dieback (flowers, leaves), spotting (leaves and fruits), or gummosis (buds, fruits) as well.

NOTE: Identification, pruning, and management of the bacterial fire blight ( Erwinia amylovora ) and fungal apple canker ( Neonectria ditissima ) on pome fruits (apple, pear, Asian pear, juneberry, etc.) are very similar to those of these stone fruit diseases. If you have any of these, emergency pruning is also necessary at this time.

ANOTHER NOTE: Some of these symptoms may be from insect pest problems. Oozing sap could be an indication of oriental fruit moth, peach twig borer, or peachtree borer getting into your shoots, trunk, or fruits. Dieback (called flagging in this case) of new shoots could be an indication of oriental fruit moth or peach twig borer. However, any entry point in your tree from insects is an open wound that could be more susceptible to fungal or bacterial infection.

Bacterial canker of plum tree (Robyn Mello) Blossom and leaf dieback are also symptomatic of infection, though there are insect pests that can cause similar appearances. (http://www.ipm.msu.edu/uploads/diseases/_full/Bacterial_canker_(blossom_blast)-WWT-E.jpg) Manifestation of advanced canker on unripe peaches. This will completely rot fruit before it ripens, and fruit left on the ground will continue to spread the disease next season. (photo credit: Robyn Mello) Blossom and leaf dieback are also symptomatic of infection, though there are insect pests that can cause similar appearances. (http://www.ipm.msu.edu/uploads/diseases/_full/Bacterial_canker_(blossom_blast)-WWT-E.jpg) Blossom and leaf dieback are also symptomatic of infection, though there are insect pests that can cause similar appearances. (http://www.ipm.msu.edu/uploads/diseases/_full/Bacterial_canker_(blossom_blast)-WWT-E.jpg) An infection may not always look like it’s oozing. Here, a dry wound may still be harboring bacteria or fungus and should be cut out. (http://livinginthegarden.net/wp-content/uploads/2015/05/057.jpg)

Always disinfect your tools with isopropyl alcohol, bleach solution, or hot water and soap before removing every new canker. One organic orchardist out of Wales disinfects his tools with milk between cuts instead, which has anti-bacterial qualities and apparently works for him.

Tools you will likely need are pruning shears, pruning saw, a sharp knife (grafting knife, pruning knife, pocket knife, or sharp kitchen knife), and possibly chisel and hammer. Placing a sheet, tarp, or large garbage bag under you while pruning may help to keep infected debris from getting lost on the ground. You’ll want to remove all material from the site.

If infections are apparent in your main trunk, thicker branches, and branch crotches connected to the main trunk or thicker branches, you may be able to get away with cutting out the infection rather than removing the entire limb. To do so, cut into the outer layer of bark a couple of inches out from where your canker is showing, and peel that back to reveal the wood underneath. Infected wood is most likely brown/black and may have gummy residue. Cut all of that brown/black wood out by notching with a knife, saw, or chisel and hammer until all that you see exposed is clean and green, healthy wood.

After cutting into a canker site, the darkened center of this wood is what the infection looks like inside the tree. If cutting canker off, make sure you have clean, green wood or you haven’t cut deeply enough. (photo credit: Robyn Mello)

If smaller branches are infected and you can’t find clean and green wood below your cut, you’ll have to prune the entire branch back to where it is clean and green, and to a bud that’s pointed in an outward direction and angle preferable for a new new branch to grow . You don’t want any brown/black discoloration anywhere to be showing behind remaining pruning cuts.

NOTE: Emergency pruning for the bacterial fire blight ( Erwinia amylovora ) and fungal apple canker ( Neonectria ditissima ) on pome fruits (apple, pear, Asian pear, juneberry, etc.) are essentially the same. Pruning out fire blight is often recommended to cut back 8” from visible infection.

Pruning tools, bottom to top: 12’ telescoping pole saw and pruner, expandable pole saw, limb spreaders of various sizes, pruning saws, 70% isopropyl alcohol, loppers, extendable pole pruner, hand pruners, gloves, and twine (Robyn Mello)

Prevention and Management:

Remove all diseased plant parts from your orchard via trash bags, adding to a well-managed and hot compost pile, or burning. Placing a sheet, tarp, or large garbage bag under you while pruning may help to keep infected debris from getting lost on the ground.

Michael Phillips, author of must-have orcharding book, The Holistic Orchard , has some great herbal tips for helping your afflicted trees , including rubbing calendula salve or garlic paste onto newly pruned wounds for their antimicrobial effects. Plants healing plants seems like a winning option! There are many other common antibacterial and antifungal plants growing in most of POP’s partner orchards, as well, such as thyme and oregano that can be used the same.

Though we generally don’t recommend sealing pruning cuts because trees are best at healing themselves, some orchardists whose trees have been heavily affected by these diseases will use organically approved Abrex Heal and Seal or similar.

Continue to monitor your trees for signs of infection or re-infection, compost well at the end of the season or beginning of the spring, and, if your orchard’s infections are quite bad, spray with copper/sulfur fungicide at the very beginning of spring next year.

High Quality Educational Videos:

This POP Disease Tip is written by Orchard Director Robyn Mello.

SUPPORT US! If you found this entry useful, informative, or inspiring, please consider a donation of any size to help POP in planting and supporting community orchards in Philadelphia: phillyorchards. org/donate.

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Disease Management

Healthy fruit trees are better able to withstand diseases. Stress avoidance as a method of disease prevention is the most important management strategy. Once a disease invades a fruit tree, it is difficult, and sometimes impossible, to eradicate. Pruning infected branches back to healthy growth sometimes mitigates the spread of disease, but unhealthy trees are likely to develop more diseased tissue. Fungicides and bactericides may also retard disease symptoms, but they are most effective when applied as preventive treatments instead of after diseases take hold. Planting in well-draining soil, watering and fertilizing according to recommendations, and preventing mechanical injury from mower blades and string trimmers are strategies that help maintain optimal tree health.

Victoria Lee Blackstone is a horticulturist and a professional writer who has authored research-based scientific/technical papers, horticultural articles, and magazine and newspaper articles. After studying botany and microbiology at Clemson University, Blackstone was hired as a University of Georgia Master Gardener Coordinator. She is also a former mortgage acquisition specialist for Freddie Mac in Atlanta, GA.

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