How to Prevent and Get Rid of Bacterial Canker

If you have a small farm or homestead, you’ve likely considered the many benefits of growing ornamental or fruit trees. While trees are beautiful statement pieces on any property, requiring minimal attention and care, there is one disease that is known to afflict fruit trees that can make your work a lot harder.

Has your tree begun to develop sunken wounds that weep a rusty-looking liquid? If so, you may be dealing with a bacterial canker infection.

Bacterial speck on tomato

What is Bacterial Canker?

This disease is caused by a bacteria, Pseudomonas syringae, that regularly coexists peacefully with host trees. As a weak pathogen, it usually does not present any issues and can go for several years unnoticed.

It goes by several other names, like sour sap and gummosis, and this usually harmless pathogen can be found in apple and pear trees as well as on all stone fruit trees (like cherries). It can infect both ornamental and fruit-bearing trees, causing the canker to kill branches and bark until the tree eventually dies.

This disease infects the leaves and stems of these species, with cankers forming in mid-spring and causing issues throughout the summer and early fall.

It enters the tree through injured bark or through a wound, such as a pruning cut on a branch. Frost damage can also lead to infections. They are spread through cool, wet weather, either by the rain itself or through pruning tools.

Once bacteria sets in, it’s difficult to get rid of. It will live in infected buds and on the surface of both healthy and infected weeds and trees. It can also overwinter in cankers or in systemically infected branches or buds. This bacteria can also live on the leaves of many plants, including many common weed species.

Signs of Bacterial Canker

Bacterial canker usually emerges with symptoms in the spring and early summer. You will notice signs in several areas of the tree, with the most pronounced symptoms appearing on the spurs and stems of the plant.

You may notice sunken, dead-looking areas of bark. These will appear with a sticky ooze. The infection will rapidly spread but you should look for other symptoms that accompany this oozing, also known as gum production.

Gum production is not uncommon in many tree species, and if there isn’t any sunken or dead-looking bark, you may not have anything to worry about.

Check the shoots of the tree as well. If shoots are not emerging or if they start to grow normally in the spring and then die back rapidly, you may have an issue with bacterial canker.

This can infect a large majority of the shoots on a tree in extreme cases. Dieback of shoots can also be caused by blossom wilt, so make sure you are watching for the other signs of bacterial canker, too.

Cankers will often develop on the base of the buds. On the limbs or trunks of the tree, the cankers are usually darker than the normal bark and will look sunken in the center.

Finally, the loves of your tree will develop small brown dots. These will look round and will fall out, leaving holes in the tree. It may look as though your tree has been hit with a shotgun blast.

When your trees are infected, they will develop cankers. These cankers are the result of bacterial cells gaining entry through leaf scars or wounds when the leaves fall. These cankers usually are dormant throughout the summer months, but become a problem when the trees exit dormancy in the early spring. The cankers will be large and often have a sour smell.

Why is Bacterial Canker a Problem?

In many cases, bacterial canker can be successfully treated with nary a damage to the tree. However, in severe cases, bacterial canker can become systemic, infecting the branches, fruit, and flowers of the tree. The tree may experience largescale twig dieback, the death of larger branches, or even the death of a tree.

At the very least, if your tree is trying to fight a bacterial canker infection, the likelihood of collecting a healthy, substantial fruit harvest is reduced. A tree that is stressed by disease simply won’t be as productive as a healthy, uninfected one.

How to Prevent Bacterial Canker

When it comes to addressing bacterial canker, an ounce of prevention is worth a pound of cure. Consider these tips for eliminating the likelihood of bacterial canker -as well as other diseases – from appearing in your backyard orchard in the first place.

Avoid Stress

Trees usually become infected with bacterial canker, as well as other diseases, when they are stressed. If your trees are not received the proper nutrients or are subjected to intense weather conditions, they are more likely to become infected with this disease. When you plant your trees, avoid planting them in hard soils, which will make it difficult to root.

You should also check the pH and nutrient content of the soil at planting -as well as on an annual basis – to make sure your soil is not depleted of necessary nutrients. You can add lime, aged compost, or other amendments to keep your soil healthy.

Always check the nutrient content of your soil before applying any fertilizer. Too much nitrogen, particularly in the form of nitrogen-rich synthetic fertilizers or manure, can cause excessive soft growth that is extremely vulnerable to infection.

Consider a Protective Foliar Spray

If your tree is nutrient deficient in some way, a foliar spray may help. You can use a foliar spray comprised of various micronutrients, like boron or zinc, to protect your tree from bacterial canker damage. These should be applied in the fall or spring.

Get Rid of Nematodes

Nematodes are unique creatures in that they can increase tree stress levels. Carefully fumigate your planting site and select species of trees that are grafted onto nematode resistant rootstocks. For example, huardian rootstocks can be very resistant to nematodes (which are tiny roundworms that can cause extensive damage).

Invest in High-Quality Rootstock

Some rootstocks are tolerant and resistant to bacterial canker. If you haven’t yet purchased a tree, consider investing in one of these resistant stocks. You can also purchase a hybrid, which tends to be more resistant to most diseases.

Practice Preventative Pruning

Pruning is a great way to reduce the likelihood of bacterial canker becoming a problem, and it’s also a good way to treat it once it emerges. You should do all of your preventative pruning in July or August, when the trees are more resistant to infectious damage, but you can do any treatment pruning in the winter.

Keep Things Dry

It can be difficult to keep conditions dry once you’ve already planted your trees, but to the greatest extent possible, try to select a dry planting site for your fruit trees. Bacterial canker is more common during periods of cold, wet weather after bloom. This is when you will notice more leaf spots.

Periods of heavy rain and high winds, accompanied by low temperatures, produce an environment that is most favorable for infection. Select a planting site that has good internal soil drainage and that is more or less protected from the elements.

Removing weeds and grass from the base of your tree can also help prevent the spread or occurrence of this disease. Unwanted plant matter can keep the ground too damp. It can also prevent adequate air circulation.

Keep Things Clean

Bacterial canker is a severe disease, but it can more easily be prevented by keeping things hygienic. This infection is more common, as well as more damaging, on trees that are injured.

To avoid this, make sure you sanitize your pruning tools before and after each pruning. If you have a tree that has a known history of bacterial canker, you need to be especially careful with this.

To disinfect your tools, use a mixture of one part bleach to for parts water. This will help remove any lingering bacteria or other diseases that can infect your plant.

How to Get Rid of Bacterial Canker

It’s definitely easier to prevent bacterial canker than it is to treat it, but there are some easy steps you can take to get rid of it once it’s set in.

Mechanical Removal

The easiest way to get rid of bacterial canker is to remove any infected branches. You should use sterile pruning tools and wait until late winter to do this. When the tree is in a state of cold-weather – induced dormancy, you will be less likely to reinfect the tree and this task will be easier to complete.

When you’re ready to prune back the dead branches, you should peel the bark back until you view clean white flesh. This will allow you to see where the cankers end. Cut at least six inches past the wound close to the tree. This will ensure that you remove areas where the bacteria has already spread but not yet begun to show symptoms.

Make sure you also cauterize the wound where you remove the branch to prevent reinfection. This can be done by hitting it with a handheld propane torch. You can also paint the wood with a wound paint, which will protect it from reinfection.

When you’re done pruning the tree, make sure you dispose of the damaged branches immediately. Do not compost them, but instead burn them or throw them in the trash. This will reduce the likelihood that the bacteria will spread to other trees.

Paint Your Tree

No artistic skill required here, but painting your tree can help seal out some of the damage caused by bacterial canker. You should brush damaged ark with white latex paint (diluted down with water) to help reduce the impact of temperature fluctuations on the bark.

Fungicidal Sprays

Unfortunately, there are very methods of chemical control available for backyard gardeners in treating and preventing bacterial canker. Fungicidal sprays are generally not effective on this disease.

That being said, you can use a copper spray in the fall. These sprays must be continued for several years, and you must wait until the majority of the leaves have dropped in the fall and before buds swell in the spring. Copper sprays do not do much to treat an infection during the growing season itself.

Can My Tree Recover From Bacterial Canker?

Bacterial canker can be a difficult disease to treat, but it’s much easier to prevent. Fortunately, a tree that has been infected with bacterial canker has not necessarily been issued a death sentence – there is plenty that you can do to help your tree prevent, deal with, and recover from this nasty disease.

Follow these tips and you won’t have to worry about bacterial canker becoming a permanent issue in your backyard orchard. What are other tips or tricks do you have for preventing or treating bacterial canker?

Be sure to let us know in the comments, and don’t forget to pin this using the image below!

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2 thoughts on “How to Prevent and Get Rid of Bacterial Canker”

  1. I have three apple trees which were over 8ft high when put in so I reduced most of the top branches in February following a very dry spring they all have canker 18″ above ground level is there anything I can do to save them.They all have some fruit but also new growths which look poorly with some leaf curl.

    During the last 2-3 weeks I have since given them plenty of water and some extra nutrient is there anything else I can do to save them? I am in Mudeford Dorset

    1. I’m no pro. I’ve read several articles though. If the spots are isolated you can try cutting it out with a knife, than torching it a bit, and then putting on tree sealer.

      On youtube there is an instance where an orchard was able to reverse a bad infection through nutrition. But this involved using Sap Analysis and then giving lots of the nutrients the tree was missing. By giving the trees what they needed they were able to fight off the infections. So try doing lots of foliar feeding of both major and micronutrients.

      Start with Alaska FIsh Emulsiona and Alaska Pure Kelp and Southern Ag’s Citris Spray. Put it both on the leaves after dark and in the ground. And try to baby the trees the best you can.

      I planted 8 trees this spring. I ripped some of the roots on one of my cherry trees getting it out of the pot. So I babied it using the above and managed to save it through the transplant shock. High summer heat in Florida (not the place for cherry trees either). But its now growing new shoots. So I think the roots are catching up.

      Problem is I think I have one spot on the tree with gumosiss and its might be bacterial spot. My plan is to watch it a few more days. And when it gets to a dry period I’m thinking of cutting it out now. The article above says to wait till tree is dormant but man I dunno. I think maybe best to get on with it.

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