peaches unaffected by bacterial canker

How to Kill Bacterial Spot, Gum Spot and Bacterial Canker in Apricots, Peaches, Plums and Prunes

Apricots, peaches, prunes and plums are all stone fruit. The trees of these fruits are under constant attack during their developmental stages. Some of the diseases that often threaten these stone fruits include bacteria canker and bacteria spots. While these diseases are aggressive, they are treatable and preventable. In this article, we will be exploring solutions of how to rid your fruits of Bacteria Spots and Bacteria Canker.

Bacterial Canker

Bacterial canker is caused by the bacterium, Pseudomonas syringae. The bacterium enters the tree through wounds left on the tree. These wounds may be as the result of previous pruning exercises, and in some cases, frost damage. Infections are common during autumn, winter and in early spring seasons. The bacteria thrives under damp conditions. The bacterium is spread by rainwater or poorly cleaned pruning tools.

Should the canker manage to form a ring around a branch or limb of the tree, all the leaves in that area will curl in and turn yellow.  Also, the area stops growing and eventually dies. Similarly, the same result can be expected if a ring forms in a region around the trunk of the entire tree.

bacterial canker on leaves


There are various symptoms that indicate the presence of bacterial canker. The first of these symptoms is the formation of gummy wounds on the tree trunk or on the twigs. These wounds produce a foul-smelling sap that oozes out of the tree. The affected areas also begin to appear darker than the unaffected healthy regions. The moment you notice such signs, it is time to start thinking of a line of action to treat bacterial canker.

Prevention and Treatment

When it comes to preventing the infection, the most important thing is to keep the tree healthy. Healthy trees are less susceptible to the causative bacteria. Trees most likely to get infected are those in locations where ring nematodes flourishes. Likewise, damp and frost environment are excellent breeding grounds for the bacteria.

Using any culture method like good irrigation methods and providing nitrogen to plants are a few ways to keep a tree healthy. Also, fumigation, before planting takes place, is encouraged as it helps to keep ring nematodes in check.

Taking caution to prevent ring nematodes is the best form of treatment for bacterial canker in stone fruits. It is often said that that prevention is better than cure. However, in the event of an infection, below are some simple treatments to follow to get rid of the bacterial canker infection.

peaches without bacterial spot
bacterial canker on plum tree

Treatment Steps

  • Flowering trees should be pruned when they are blooming; it will make any wound heal faster.
  • Cut off and get rid of dead tree limbs and any other infected parts.
  • Bacteria are more functional in early spring and autumn. Avoid pruning during these periods.
  • Using copper-based chemicals like Copper Oxychloride (also known as dicopper chloride trihydroxide or Demildex) to spray infected areas. It will prevent the re-infection of present lesions. The chemical is easy to prepare. Simply adding water and stirring it up in a plastic container is enough.

Bacterial Spot

Bacterial Spot is caused by the bacterium Xanthomonas pruni. It is known to affect leaves, fruits and twigs. Chronic infections have been known to cause severe drops in fruit quality and harvest. Under favourable conditions, the disease can spread to more than half the produce. The disease is spread by falling rain and wind. It is most active in regions of warm temperatures and light rains. However, it is dormant in hot and dry weather.

In cases of chronic infections, the leaves fall earlier than expected – early defoliation. Early defoliation can cause the tree to become weak and less vigorous. As a result, it is prone to more damage in the winter. Also, when the infection is severe, the tree becomes susceptible to fruit diseases such as brown rot and rhizopus. There is also a chance that the tree will become a host for many insects and pests. In addition, the fruit size reduces, and the fruit is likely to become sunburnt. In some case, the fruits start to crack while still on the tree.

rotten peaches


Leaf: Irregular and angular spots appear on the leaves. The spots are usually brown or black. They can also appear as dark purple spot. When the spots converge into a larger form they make the tree leaves appear charred.

Fruits: On the fruits, the spots can appear to be brown or black. They are usually surrounded by a soaked margin. For peaches, the spots appear on the sides facing the sun. Meanwhile, plums show slight differences like the black spots may be larger or appear in small pit-like lesions forms.

Twigs: There are two types of infection that twigs exhibit. Spring cankers are known to form on young twigs that grew during the summer. At first, they look like dark blisters that have a lot of pus in them. With time, the blisters will break, releasing the bacteria onto the tree surface. Summer cankers form on twigs when the tree is already showing signs of leaf spot.

bacterial spot on tree

Prevention and Treatment

As with bacterial canker, there is nothing quite as good as maintaining a healthy tree to prevent infection. Providing the necessary nutrients and a good supply of water is enough to protect the tree from disease. Strong healthy trees are not as prone to infection as weak trees.  Also using cultural practices that help the plum tree dry faster will drastically cut down the risk of infection.

Furthermore, avoid planting in areas with limited access to both sunlight and air. Areas with good drainage are good spots to plant. Prune trees early and continuously work on improving the airflow around the tree. Pruning is best done in dry seasons. It is advisable to select a variety of seed to help build resistance to infection. Fertilizing the soil on time will also help the trees grow into stronger and healthier trees.

There is no sure-kill chemical for treating this infection. Nevertheless, using copper-based chemicals like copper-oxychloride (Demildex) have shown significant results in regards to fighting off the infection. It’s best that these chemicals are used in preventing rather than treating the disease. The initial application focuses on reducing the chances of contamination on the leaf. Later applications may be done to protect the fruit when they start to blossom out from the husk. The chemical’s effectiveness will vary with the length of the infection.

When spraying ensure that you are well-protected from spills and that your face is well-guarded. Spraying is best done in the morning of a dry and sunny day. After application, the plants should be given time to dry off. As a precaution, the chemical mixture should be prevented from penetrating the tissue of the leaves.

diseased tree
a healthy peach

The Copper Oxychloride (Demildex) works by cutting of the operation of the enzyme system of spores. In so doing, there is irreversible damage to the plant. Nevertheless, it forms a protective chemical barrier against infection.  It is better to use Demildex compared to other bactericides because;

  • Lead and other such metals are reduced during production.
  • Its smaller size (1.58 microns) helps it cling to plant surfaces better than others (around 3.13 microns or more).
  • Copper chloride content is also reduced during production.
  • It continuously works against bacteria, and fungus growth once applied.

In conclusion, if you care about your apricots, peaches, plums and plum, it is crucial that you always monitor the trees for infection. It is not enough to treat infection, take preventive measures to avoid severe damage to the fruits. Lastly, should there be an infection, take swift actions as highlighted in this post to get rid of the disease, especially if they are bacterial spots and bacterial canker.

copper oxychloride demildex used to treat black spots on roses