After Fire in Avocado Orchards, Stop!
Avocado orchards are often right in the thick of fire because of their location near wildlands. Every year many trees are fire damaged, but most trees don’t die, they get toasted. That’s because a fast-moving fire often only heats up the canopy and low hanging fruit and moves on without causing significant burn damage to the trunk and structure.
Orchard recovery after a fire requires flexibility and close observation of the trees. Recovery may take multiple years. Below are some suggested steps to follow if your trees have been affected by a fire.
- Initially do nothing other than to repair the irrigation system and reduce water application amounts to affected trees where the canopy has burned. Even if no canopy exists, a short irrigation should be made for perhaps an hour or two to keep the feeder roots alive, which will help the tree recover. The water needs of an avocado or any plant are dependent upon the foliage, therefore, if there is no canopy then little water is needed. In fact, continuing to apply significant amounts of water to a tree without a canopy can increase the chances of root rot or other diseases hurting or killing the tree. If there is little canopy remaining after the fire, stop significant watering until a significant amount of the canopy has re-grown. Apply only enough water to keep the feeder roots in a moist but not wet soil, which will likely mean that infrequent and shorter water applications are needed.
- After about three months during the growing season (longer if the fire happens in late fall/winter) you will see re-growth in the trees that are still alive. Apply more water as you start to see the canopy recover but be careful not to overwater. At this point, the tree is likely at a state where you will be able to determine which portions of the tree need to be pruned and which trees are dead and need to be removed. It is best to wait until six months have passed to make this decision. The viable wood remaining on the tree will provide the resources the tree needs to regenerate and premature pruning might remove some of this wood. Additionally, the branches and leaves will provide sun protection while the tree continues to recover. Applying a whitewash to the entire tree will further protect it from sunburn.
- Before spending any significant amount of time or money the entire grove should be evaluated. An orchard with a wide range of tree sizes and ages on different rootstocks can be difficult to manage and irrigate. If more than 50% of the trees are destroyed, consider removing the remaining trees and replanting. Many of the "surviving" trees may be so damaged that even though they may appear to be recovering they are likely to die anyway.
- If the long-term viability of the orchard is in question, it might be worth considering tree replacement with a new tree grafted on a superior clonal rootstock, which may improve long-term production for the grove.
- Trees which have had more than about 50% of the circumference destroyed will need to be replaced.
- Even a small fire can significantly stress trees. Applications of phosphorous acid can help protect the trees from root rot, which is especially important when a tree has been stressed.
- Hold off on fertilizer application until the following year and apply in smaller amounts.
- Apply mulch to protect the roots and promote increased growth rates. The root system of a healthy avocado tree is growing in natural mulch created by the fallen leaves of the tree itself. After a fire, these leaves have likely burned, and the canopy of the tree is gone as well so direct sunlight on the soil can damage the sensitive shallow feeder roots if left unprotected. A four inch or greater layer of mulch will protect these roots until the tree recovers and reproduces its own natural leaf litter mulch.
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