Identifying Herbicide Injury to California Avocado Trees

For California avocado growers, it can be difficult to ascertain whether a tree is suffering from disease, pests, nutrient deficiencies or damage caused by insecticides. Dr. Travis Bean’s new blog post examines herbicide damage in California avocado groves, including the specific symptoms associated with different insecticide groups.

Herbicide injury can impact the yield, number of fruit, plant vigor and health of California avocado trees. In most cases, damage occurs because of spray drift, improper application of the herbicide and tank contamination.

When assessing trees, it may be difficult to determine whether a damaged tree has been impacted by an herbicide or some other environmental stressor. In general, if a tree appears “damaged” on just one side, then this could be an indicator of pesticide spray drift. If damage is only visible along the edge of the tree’s skirts, then it’s likely an indicator of uneven ground spray application.

To determine the specific cause of the damage, Dr. Bean notes it’s important to examine a number of factors. Take soil and plant tissue samples, note symptoms and injuries, record herbicide use and weather conditions and determine whether other plant species in the orchard are affected.

The Weed Science Society of America categorizes herbicides by Mechanism of Action (MOA) —the biological processes each herbicide disrupts. Each group has specific injury symptoms that can help California avocado growers determine whether tree damage has potentially been caused by a specific herbicide they are using. For example, Norflurazon damage leads to white/bleached plant foliage. Dr. Bean’s blog post includes a table of eight of the most common herbicides used in California avocado groves and their injury symptoms. In addition, a complete searchable database of pesticide injury images, MOAs and injury symptoms can be found online.