Shot Hole Disease (Coryneum Blight) Control & Treatment

Found mainly on the Prunus family, shot hole disease affects fruit trees including plum, peach, apricot, and cherry varieties. It’s often mistaken as the work of an insect but instead, it’s caused by shot hole fungus. It can affect fruiting and ornamental trees and displays in the forms of holes in the leaves, uneven surfaces on fruit, and deformities on the branches.

Cherry tree leaves infected with shot hole disease / coryneum blight
Cherry tree leaves infected with shot hole disease.
Gypsypitcrew, CC BY-SA 4.0, via Wikimedia Commons
shot hole disease / coryneum blight infection on peach tree leaves
Peach tree leaves suffering a shot hole infection. Note the brown spots forming as an initial sign of disease.
CoolKoon, CC BY-SA 4.0 , via Wikimedia Commons

This fungus affects stone fruits and is caused by the pathogen Stigmina carpophila. When the infection takes a firm hold, leaves will begin to  fall off the tree. In serious cases, fruit production will be severely hindered. The spores of this disease are spread through moisture and spread well during rainy weather. Severe instances of shot hole hinder the photosynthesis process.

Shot Hole Disease Symptoms

As previously mentioned, at first glance as the Coryneum Blight progresses, you may mistake shot hole infection with insect damage. However, when you take a closer look you will be able to determine quickly if your tree is infected with shot hole disease.

Symptoms On The Fruit Tree:

  • Symptoms begin with red or brown spots with a yellowish ring around them on the leaves themselves.
  • As the disease takes hold, the infected parts of the leaves fall away, leaving “BB” sized holes behind.
  • As shot hole disease spreads, the leaves will continue to see damage until they fall off.
  • Infected fruit may have purple spots on them that will turn into white lesions. There will be rough areas to the fruit as well.
  • Branches can become diseased and weakened and infected buds may appear darker in colour compared to healthy ones.

Shot Hole Disease Treatment & Control

Rain and moisture causes shot hole disease to spread quickly so the quicker you take action, the less damage there will be. Prolonged wet periods will accelerate this disease so be mindful of checking after particularly wet weather. Damage from Coryneum Blight will be most noticeable in the spring months, so keep a watchful eye on your fruit trees.

Organic Treatment & Control

Organic treatment and control of shot hole disease can be achieved through a combination of good orchard hygiene, and immediate pruning of any leaves and branches showing signs of infection. You can also make use of natural anti fungal sprays.

  • Regular pruning of weak branches and shoots can help keep this disease at bay. Any infected leaves and branches should be immediately removed and destroyed.
  • Overhead watering should be avoided as this encourages the disease to spread more quickly.
  • Being aware that spores travel through moisture can help you observe any potential symptoms.
  • Regularly check the leaves for brown or red circles or BB-sized holes.
  • Try to sterilise your pruning equipment after each use.
  • Use an organic anti fungal treatment to kill the infection if you notice the disease has taken hold on your fruit tree.

Pesticide Treatment & Control

You will need to take pesticide control measures once this bacterial or fungus infection takes hold. This can help minimise the damage.

  • Treatment is most effective when the new shoots are appearing.
  • There are also sprays you can use other times of the year which will act as a preventative.

Biology & Lifecycle

Shot hole is spread through environmental conditions – particularly when you bring together warm and wet conditions. Young trees are most susceptible to this bacterial or fungus infection, the older the tree gets the less this problem should occur. Infected spores can lie dormant for many months until conditions are right. When the weather warms up and water droplets remain on leaves, you can witness a fast spread of this disease.

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