Ask The County Agent: Ambrosia Beetles can seriously damage trees, shrubs

Pictured above: Female Ambrosia beetles dig tunnels to lay eggs and create toothpick-like structures that come out of the tree trunk. Photo Credit: North Carolina Cooperative Extension

By STEPHANIE BUTCHER, UGA Coweta County Extension Coordinator

QUESTION: Ambrosia beetles attacked my fig tree. Can I save my tree? 

AGENT:  Granulated ambrosia beetles are a serious invasive pest of trees and shrubs in Georgia. Whether or not your tree can survive an attack depends on the extent of the damage.

As the female beetles dig tunnels to lay eggs, they create toothpick-like structures that come out of the trunk or stem. This is a sure sign that you have ambrosia beetle damage. Sometimes wind and rain can cause the fragile “toothpicks” to fall, so look for them at the base of the tree and inspect the trunk and branches for tiny holes too.

If your tree is vigorous enough, the beetles may be drowned or forced out by heavy sap flow. However, if the tree is weak or not producing large amounts of sap, then the attack could be successful. 

Ambrosia beetles commonly attack weak or dying plants, such as fig trees that were damaged by freezing temperatures or waterlogged soils. Environmental conditions this year may have weakened some trees and made them more susceptible to beetle activity. 

Adults and larvae bore into twigs, branches, or small trunks of woody host plants, excavate a system of tunnels in the wood or pith, and introduce a symbiotic ambrosial fungus. The beetles are highly specialized and feed on fungi they cultivate on the walls of the galleries. Both the adults and larvae feed on the fungus. This fungus and tunneling will damage and clog the plant’s tissue that transports water, called xylem. This ultimately kills all or part of the plant. 

The beetles are active during warm periods of the year, but you will not usually see the adults. Most of the time, they are inside the tree and the damage is done by the time you see evidence that they are present. They breed in stems that are 2 to 30 cm in diameter. Smaller branches are usually attacked first. 

When female beetles mature, they leave infested plants and fly to new host plants. And they don’t just attack fig trees. Ambrosia beetles are known to attack pecan, peach, plum, cherry, persimmon, oak, elm, sweet gum, magnolia, buckeye, crape myrtle, maple, and dogwood too. 

Controlling ambrosia beetles is difficult. Heavily infested plants or plant stems should be pruned out and burned. Insecticide sprays do not work when applied to an already infected plant. 

To help reduce the spread of infection to other susceptible trees and shrubs in your landscape, you can apply a preventative insecticide spray (permethrin or bifenthrin), but it must be applied to healthy plants before adult beetles emerge from their host plant and move on to attack the new plant.

Using proper horticultural practices to keep plants healthy will help prevent future attacks. This includes maintaining the soil pH and properly fertilizing based on a soil test. 

For more information about growing figs or pest control in landscape plants, contact the Coweta County Extension office at 770-254-2620 or [email protected] and ask for the publications, “Home Garden Figs” or “Control of Common Pests of Landscape Plants.” 

The University of Georgia College of Agricultural & Environmental Sciences is an equal opportunity, affirmative action organization. 

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