Effects of 2018 Fires and July Heat Wave on California Avocados

  • Oct 08, 2018

A recent blog post by Dr. Ben Faber provides an overview of the after effects of the 2018 wildfires and July heat wave on the current and future California avocado crops.

Following the December wildfires in California, many of the trees damaged by fire, heat and gases began to re-leaf and flower in the spring. Unfortunately, the mild weather was suddenly interrupted by an excessive heat event July 6 – 8 with temperatures in excess of 120˙F. Because the spring and early summer were mild, California avocado trees did not have the opportunity to acclimate to rising temperatures and were caught off guard by the sudden extreme heat. Tree stomates, which act to cool a tree, had to transpire at unusually high rates. Because avocado trees have shallow root systems, they are more susceptible to rapid transpiration. As a result, water flow to the canopy was shut off, leading to the browning and death of foliage and buds. Young trees and trees recovering from fire damage were the most severely affected.

As the canopies wilted, California avocado trees were further damaged by sunburn. Dr. Faber notes that branches that were not whitewashed may never fully recover from the burns.

In addition, fruit also was affected by the excessive heat. Mature fruit softened and became unmarketable; many avocados simply dropped off trees. Fruit that was set on the tree for the 2019 season also shriveled and dropped. As for the fruit that was harvested, the heat may have affected the oils in the avocados leading to a decrease in fruit quality. Because the heat wave took place in July, many trees suffered damage to the summer flush that was set to produce fruit for 2020.

For now, growers should continue to clean up the affected trees to prevent the spread of disease and sunburn. Damaged trees should be whitewashed to prevent sunburn and dead leaves and branches should be removed to prevent the spread of fungal diseases.

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