Protecting California Avocado Trees from Red Imported Fire Ants

  • Feb 22, 2023

A recent article in the Topics in Subtropics newsletter notes red imported fire ants were found to be girdling and killing young avocado trees in the summer of 2022. Dr. Peggy Mauk of UC-Riverside observed the fire ants at UCR’s research station in Riverside and determined approximately 2% of the trees had died as a result of the girdling.

As soil temperatures begin to warm with the onset of spring, it is important California avocado groves are monitored for imported red fire ant activity by young avocado trees. The easiest way to distinguish the red imported fire ants from other ants is to observe its openly aggressive behavior when a nest is disturbed — they will quickly climb onto and sting anything touching their mound. The mounds are typically dome-shaped and often resemble gopher mounds. Imported red fire ants also will build nests in rotten logs, the walls of buildings, in outdoor utility boxes or under sidewalks.

Dr. Mauk’s team controlled the fire ants at the research station with two applications of commercial fire ant bait. The baits are inexpensive, effective and safe for the environment. Baits tend to be more effective than spraying a nest because the ants carry the bait poison back to the nest whereas spraying a nest may lead to the pests dispersing. Baits should be placed where ants are seen walking. If daytime temperatures rise above 90˚F, baits should be placed during the evening when it is cooler. Baits also should be placed on dry ground to avoid deterioration.

When choosing a bait, check the label for “fire ant bait.” Mound treatments and broadcast granules with cyfluthrin, deltamethrin, pyrethrin, acephate, d-limonene, permethrin, bifenthrin and lambda-cyhalothrin are not recommended, as they do not produce good long-term results that will effectively reduce the colony. A list of baits is available on the UC-Riverside red imported fire ant webpage.

More information concerning red imported fire ant management practices is available on the UC-Riverside Integrated Pest Management webpage.

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