Pruning Wound Cankers Found in Almond Trees

Making pruning cuts on almond trees is risky business. Every cut provides the opportunity for fungal/bacterial pathogens to enter the tree (Think: a cut on you hand can allow bacteria to enter). Once the pathogens enter the tree and successfully colonize, poor tree performance and shortened orchard life can be expected.

Figure 1: Fungal canker associated with a pruning wound on a young tree. Upon bark removal, canker growth and damage is evident.

Fungi are the most commonly found pathogens invading tree wounds. In figure 1, a large pruning cut was made on a super-vigorous first leaf almond. The pruning wound became infected with the fungi Eutypa which grew through the tree causing a large canker. This canker did not become noticeable until the third leaf. Upon bark removal, it is clear that the canker grows outward from the point of origin. As the canker continues to grow, it has the ability to kill branches by girdling (Figure 2), weaken scaffolds which then break (Figure 3), and/or killing the tree by girdling the trunk (Figure 4). Botryosphaeria is another fungi that may cause this problem.

Figure 2: Scaffold killed by fungal canker girdling the vascular tissues of the branch.

Figure 3: Scaffold split caused by weakening of crotch angle by invading fungi.

Figure 4: Tree killed by wood fungal canker girdling the vascular tissue of the tree trunk. Bark removal shows the advancement of the canker.

Irregardless of the possible infection by fungi, trees need to be pruned to shape (young trees), remove unwanted branches, and remove dead/diseased tissue. Knowing this, how can we prune the tree and reduce the chance of fungal infection? Most fungi require moisture/high humidity/rain event to produce spores. These spores are usually transferred by wind-blown rain.

The “window of opportunity” for these fungi to infect almond trees occurs when the tree has an open wound. Large cuts (larger than a quarter) made on an almond tree may take up to 14 days to heal, while smaller cuts can take up to 10 days. This open wound can provide a point of infection for fungi until the cut tissue “heals.” At this point it becomes resistant to most infections. To prevent these types of problems, it is advised that growers prune their trees when rain is not forecasted for the foreseeable future (7-10 days). For super-vigorous first/second leaf trees, consideration should be made to prune unwanted branches during a period of low humidity (late summer/early fall). Available pruning wound paints do not appear to be effective in preventing invasion by Eutypa and Botryosphaeria in almond.

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3 thoughts on “Pruning Wound Cankers Found in Almond Trees

  1. Is it manditory to prune a first year almond tree? Can I wait untill the second year when u have a better limb selection?

  2. Waiting till the second year to make the primary scaffold selection is not recommended fro the following reasons:
    1. It will be more difficult to select a branch and make a clean, correct cut due to crowding within the crotch area of the tree.
    2. All of the energy that the tree placed into the development of the branch is wasted – since it is removed from the tree. The amount of energy used is much less than the first year.
    3. Cutting away that much new growth will set you back at least one year, maybe two, since the ratio of shoot to root is now thrown off. So your third leaf trees will look like most people’s second leaf trees.
    4. Larger pruning cuts will have to be made, taking longer to heal, therefore being more susceptible to the diseases mentioned above.

    I hope this helps in your decision making process.

  3. Pingback: When to Prune First Leaf Almonds - The Almond Doctor

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