Fire ants have been problematic this summer in newly planted satsuma trees. This was a problem new to us; as we are learning a lot about citrus from our first-time growers and we wanted to share some info on how they can damage trees, and provide some solutions.
Here is an excerpt from the University of Florida’s Citrus Production Guide
Fire Ants
While fire ants (Solenopsis invicta) are largely predaceous and may attack pests such as citrus leafminer larvae or newly hatched root weevil larvae, some situations can favor a high density of fire ants and lead to direct damage to citrus. For example, trunk wraps applied to very young trees can provide a protected environment for fire ants to attack tender young bark. Density of fire ants can also dramatically increase on soil mounted to protect young trees from frost. Fire ant damage to trunks of young trees produces sap flows that are collected by the ants. Girdling and death of the tree may result from direct effects of ant feeding and/or foot rot caused by infection of Phytophthora. Leaf buds may also be damaged by feeding. High densities of fire ant mounds can create problems for grove workers during maintenance of irrigation systems and for fruit pickers at harvest. Long-term control is best obtained with food baits, although soil applications of contact insecticides or even foliar applications of oil may provide temporary relief sometimes needed during harvest.
Here are some photos of young satsuma trees with girdled trunks from fire ant damage.
Here are a couple trees where the girdling was appearing to severely damage or kill the tree.
Overall, it is important to put out a residual or bait insecticide in the spring as ants become active for long term protection through the summer into fall.
Here are some labeled fire ant baits from the University of Florida’s Citrus Production Guide