Georgia pecan growers should be monitoring for ambrosia beetle now, especially if they have planted new trees or their orchards include trees that are less than three years old. The tell-tale sawdust “toothpicks” sticking out of trees is a sure sign of ambrosia beetles boring into trees.
Young trees are at particular risk because they are coming out of dormancy using only what small carbohydrate reserves they have to put out new leaves, making them stressed and vulnerable to this pest.
Ambrosia beetle, primarily Xylosandrus crassiusculus (Mot.), X. germanus and other related species, is a tiny beetle in the weevil family that attacks stressed and dead trees by boring into the heartwood of trees. There they excavate tunnels in order to cultivate fungal gardens, their sole source of nutrition.
Spring flight of this pest happens in the space of about two to three weeks when temperatures are more consistent. So, as temperatures warm, University of Georgia Cooperative Extension specialists advise monitoring for this pest early because management will need to take place as soon as growers see evidence of beetles in their orchards.
“Growers should also pay close attention to areas that are poorly drained, because trees will more likely be stressed in those areas, making them vulnerable to attack,” said UGA Extension pecan entomologist Angel Acebes-Doria. “Although trees can recover from attacks by these beetles, the higher the attack, the more likely the trees could die.”
New adaptations of previous ambrosia beetle traps have been designed to allow growers a method of identifying when ambrosia beetles are attacking trees.
The traps are called bolt or log traps and are made using freshly cut segments of young trees that have been bored out and filled with ethanol or ethyl alcohol. The traps are hung about a meter off the ground and placed between orchards and the surrounding forested areas.
Ambrosia beetles coming out of dormancy will start to move into the orchard, so they will ideally hit the traps first, allowing for rapid identification and action on the grower’s part.
Bottle traps are another tool for monitoring the presence of ambrosia beetle in orchards. They are helpful for monitoring the timing of emergence and population density of this pest but, Acebes-Doria said, seeing ambrosia beetles in traps does not mean they are actively boring into trees.
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“The beauty of using log traps is that when ambrosia beetles bore into the wood, they create visible holes and the tell-tale sawdust ‘toothpicks’ so growers can immediately see if this pest is actively attacking trees,” she said. “This helps (growers) make more informed management decisions.”
Acebes-Doria suggests growers who find beetles in their traps should initiate scouting for attacks on vulnerable trees and begin management using pyrethroid materials sprayed on trunks of infested trees. Reapply after seven to 10 days, if needed.
“Growers often ask if they can use a systemic insecticide, but because these beetles are not actually ingesting the plant tissues, these types of insecticides don’t work,” said Acebes-Doria. “For that reason, we recommend using a contact application of pyrethroids on the trunks of trees – as more of a preventative than a curative treatment.”
Once the beetles make their way inside the wood, they are difficult to control.
Acebes-Doria does not recommend spraying insecticides without first knowing for sure that ambrosia beetles are present and attacking their trees.
“That is costly and unnecessary,” she said.
This monitoring program is part of a larger collaborative project between researchers from Georgia, New York, North Carolina, Ohio, South Carolina, Tennessee and Virginia. The working group is funded through the Southern IPM Center and meets annually to provide updates on monitoring and impact of this pest in various production systems in order to develop and assess priorities year after year.
“A lot of the previous research on ambrosia beetles has been done in ornamental production systems but, in the last couple years, there have been increased issues with this pest in apple and pecan systems,” said Acebes-Doria.
Ambrosia beetles have an incredibly wide host range and are economically significant to several commodities, she said, so this collaborative work expands the research of this pest into multiple production systems and regions.
Acebes-Doria and other researchers are in the planning phase of seeking continued funding to help further these and future research efforts. They hope to find more efficient ways of reporting trap captures online so agents and growers can stay apprised of the pest’s behavior each year.