Canker On Fruit Trees: What To Do For Trees Weeping Amber Color Sap


By: Jackie Carroll

Tree cankers that ooze orange or amber colored sap may indicate that the tree has Cytospora canker disease. The only way of fixing tree cankers caused by the disease is to prune out diseased branches. The best method of control is preventing damage that allows the airborne fungus to gain entry into the tree. Keep reading to learn more about what causes amber sap on trees and what can be done for a tree weeping amber color sap.

What is Cytospora Canker?

Cytospora cankers occur when the airborne cytospora fungus enters a tree through injuries and damage. It forms a sunken canker that spreads gradually, eventually girdling the branch and killing everything beyond the site of the canker. The diseased area may become covered with a growth of black fungus.

What Causes Amber Sap on Trees?

Cytospora canker is caused by the fungus Cytospora chrysosperma. The fungus enters the tree through damaged bark. The types of damage that leave the tree susceptible to infection include pruning wounds, flying debris from lawn mowers, string trimmer injuries, frost, fire, and cat scratches.

Tiny, bumpy fruiting bodies, called pycnidia, form on the dead tissue, giving the bark a rough texture. The pycnidia ooze an orange or amber, jelly-like sap that stains and discolors the bark. Symptoms are seen on a variety of fruit and shade trees throughout the United States.

How to Control Cankers

There is no cure for cytospora canker on fruit trees and shade trees, but you can control the spread of the disease by pruning out the infected area. In late winter or early spring, remove infected branches at least 4 inches (10 cm.) below the canker where the tree is weeping amber color sap. Disinfect pruners between cuts with a disinfectant spray or ten percent bleach solution. If you use bleach on your pruners wash, rinse, and dry them before putting them away to prevent corrosion.

Proper tree maintenance that prevents stress goes a long way toward helping a tree resist disease and recover from cytospora canker. Water the tree slowly and deeply during dry periods. Fertilize annually in late winter or spring with a low-nitrogen, high-potassium fertilizer.

Prune regularly so that you don’t have to make severe cuts later on. Remove dead, damaged, and weak twigs and branches that may provide an entry point for disease and never leave stubs attached to trunks or large branches. Remember to disinfect your pruners.

Avoid injuring trees when performing lawn maintenance. Raise the mower blades high enough so that they won’t nick exposed roots and mow so that debris flies away from the tree rather than toward it. Use string trimmers with care to prevent cuts in the bark of the tree.

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The most common host of Phytophthora bleeding canker is European beech (Fagus sylvatica). Additional hosts in the region include: maple (Acer), American beech (F. grandifolia), birch (Betula), magnolia (Magnolia), dogwood (Cornus), oak (Quercus), horsechestnut (Aesculus hippocastanum) and walnut (Juglans).

Phytophthora bleeding canker kills the bark and outer sapwood tissues of trees and shrubs. The most prominent symptom of the disease is dark-colored sap oozing from bark cankers. The fluid is typically reddish-brown and it stains the surrounding bark as it flows downward. Infected bark is often water soaked and stained while the inner sapwood can exhibit a range of abnormal colors (brown, bluish-green, orange and pink) depending on the particular species of Phytophthora present. The cankers typically have a well-defined margin that is clearly associated with the bleeding of sap observed from the trunk or scaffold branch. Phytophthora species do not decay wood they consume sugars in the cambium and outer sapwood. However, the resulting death of the bark and outer sapwood can provide an infection site for wood-rotting fungi to invade at a later time. Research has shown that once Phytophthora invades the outer sapwood, the pathogen can be drawn upwards in the vascular tissue to create cankers higher on the trunk or on main scaffold branches.


HOW TO TREAT CANKER

The copper fungicide Bordeaux Mixture has previously been recommended as a spray to prevent canker in fruit trees. However it has now (or soon will be) withdrawn from sale in the UK. Currently there are no alternatives which have been scientifically proven to be anywhere near as effective as Bordeaux Mixture

Various alternatives are suggested, for example aspirin solution or milk, but none have been proven to have any effect.

The only proven method of treating canker is to remove all infected wood and bark by pruning it out. If the canker is in a stem or branch this means cutting off the branch or stem below the site of infection into good clean wood. Infected wood is brown whereas clean wood is creamy green. Leave not one ounce of infected wood on the tree if you want to eradicate canker completely. Sterilise tools before and after pruning of this type and burn all pruned wood and foliage - ALL of it!

If canker affects the main trunk of the tree below a certain level it's clearly not an option to prune off all the tree. In this case you have a stark choice, either dig up the tree and start again with a new one (the option a commercial orchard would take) or to perform surgery on the trunk.

Rather than go into endless words on how to this we have found an excellent and instructional video (see end of this page) from Huw's Nursery on how to this. See also the picture below of canker affecting the main trunk of an apple tree.


We would disagree with one aspect of the video however, the sealing of the site of pruning with a sealant. Recent evidence exists which indicate that it is best to leave the wound open. It may sound a bit unusual but all the evidence indicates that trees heal wounds better if they are left open.

BEST TIME TO TREAT CANKER IN APPLE AND PEAR TREES

The video below doesn't mention it but it's best to perform the pruning for canker is in a dry spell during the dormant period for apple and pear trees (mid November to mid-February). Pruning out diseased wood at this time of year will minimise the risk of spreading the canker to other parts of the tree and other trees nearby. Canker is dormant during this period so watch the weather forecast, bide your time and wait for that elusive dry spell.

Although it's best to prune out canker in the dormant period, inspect your apple trees for canker during the year. If you notice an area that needs to be treated then spray it with red paint so that it can easily be located when return later in the year.


Comments on the Disease

Members of the fungal family Botryosphaeriaceae are known to cause branch cankers on a variety of woody hosts, including avocado. The disease was previously known as Dothiorella canker because the pathogen most often isolated at the time was known as Dothiorella gregaria (teleomorph B. ribis).

Botryosphaeriaceae spores enter and initiate infection primarily through pruning wounds on the trunk or branches. More frequent pruning, such as would occur in a high-density grove, can increase dissemination of this pathogen among trees, leading to an increase in canker development and a possible decrease in yield as branches with cankers are pruned out.

Heavy rainfall causes increased spore production and infection. Spores spread by air and rain or irrigation splash that are hitting infected tissues. Trees that are stressed are much more susceptible to this disease. Common stresses include poor irrigation, low-quality irrigation water, nutritional deficiencies, or severe insect and mite feeding. Drought stress especially promotes symptom development and triggers latent infections to develop into disease.


Transmission

Bacterial canker colonizes the surfaces of healthy plant tissues without causing disease, but can enter into living tree tissues through leaf scars or wounds created by pruning or other means. However, bacterial canker is a weak pathogen capable of spreading and causing disease only in trees that are stressed by some external factor. Healthy, vigorously growing trees are much less likely to be affected.

The rate of the spread of the pathogen within a tree depends on the condition and age of the tree, as well as environmental factors. High rainfall in the fall and winter with temperatures generally remaining above freezing favor the spread of the disease. Depending on the severity of the stress and environmental conditions, the bacterium may be limited to small twigs or, in the most severe cases, may spread rapidly within vascular tissues and lead to the death of the tree within a couple of months.


Tree Fruit Canker Removal and Scouting for Scale While Pruning.

Pruning fruit trees is an important horticultural practice that promotes proper tree vigor and canopy architecture for optimal fruit production. Generally the best time for dormant pruning pome fruit in the northeast is January through early March. Stone fruit, with the exception of sweet cherry, may be safely pruned as late as the delayed dormant and early bloom periods.

Apple and pear diseases that form overwintering cankers are fire blight, white rot, and nectria twig blight. Stone fruit diseases that form overwintering cankers are cytospora canker on peach, plum and cherry, and bacterial canker on sweet cherry. Sweet cherry should not be dormant pruned. The time to prune Sweet Cherry is after harvest to disrupt the disease cycle of bacterial canker. In general winter cuts should be made at least few inches below the infection site to remove any infected wood that is not visible. Many of these cankers can be easily removed from the canopy while pruning, however removal is generally not practicable if the infection occurs on the trunk or base of the scaffold.

Scale infestations should also be noted while pruning. Scale infestations often start in a small area of the orchard from which they build rapidly and spread. Dormant pruning offers an excellent opportunity for the grower or orchard worker to take note of new or building scale infestations that might otherwise go unnoticed until they cause significant damage. Scale insects that attack tree fruit are san jose scale and rarely, oyster shell scale in pome fruit. In addition to san jose scale, white peach scale can often be found infesting peach orchards in the south and mid-atlantic regions, especially after a string of mild winters. San jose scale can be difficult to spot if the populations aren’t large. Look for wood that looks weak or dead and has a dark grey, blackish, or ashy appearance. White peach scale is very easy to spot in the orchard. Look for bright cottony white spots that look like splashed paint. Removal of infested wood has little if any value for controlling scale populations, however it is important to note where they exist so that dormant oils and spring applications of effective materials can be planned and prioritized.


Watch the video: Gumosis on fruit trees


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