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Keep close watch on your woody plants as spring approaches; ambrosia beetles threaten, says UK Ag

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As spring approaches, nursery and orchard managers will want to keep a close watch on their woody plants for potential damage from ambrosia beetles, said Zenaida Viloria, University of Kentucky extension associate for nursery crops.

Ambrosia beetles were first detected in Kentucky in 2013 but have been in the United States since 1999. A native of Asia, the beetles likely came to this country in wood packing materials. They attack many native, woody plants. Entomologists with the UK College of Agriculture, Food and Environment have found them in the state’s orchards and nurseries.

The camphor shot borer, left, and the granulate ambrosia beetle are two insects that could cause problems for nurseries.
(Photo by Zenaida Viloria, UK research analyst)

Kentucky has two types of ambrosia beetles, the granulate ambrosia beetle and camphor shot borer. The beetles tunnel into wood leaving behind a fungus that grows in the tunnels. The fungus causes the plants to slowly dieback and eventually results in plant death. The beetles also have a symbiotic relationship with mites that can cause damage to trees.

“These beetles can be particularly troubling, as an infestation requires the grower to destroy the affected plants,” Viloria said.

A tell-tale sign of an ambrosia beetle infestation is small, wooden protrusions that look like toothpicks jutting out from the branches. These protrusions are made by the smaller ambrosia beetles, including the granulate ambrosia beetle, and are debris from the insect tunneling into the tree. The camphor shot borer is a larger beetle. Nursery owners will notice sawdust around the trunk of the plant from the borer’s tunneling. The plants will also have a round, black hole where the insect entered.

The beetles overwinter in the plant as adults and emerge each spring to look for a new host. Each year, the state sees three generations of the beetles during the growing season.

UK entomologists and nursery researchers will begin counting the beetles weekly beginning in March. This will help nursery growers know when to apply an insecticide. Insecticides are available to kill the flying insects and prevent it from boring into a woody plant.

“The best management for this insect is to have healthy trees,” Viloria said. “You want the plants to be well hydrated but not overwatered.”

With funding from the Kentucky Department of Agriculture’s Specialty Crop Program, Viloria, Win Dunwell, UK extension horticulture specialist, and UK entomologist Raul Villanueva will trap the insects and look at various management techniques to help Kentucky growers better manage the insect starting this spring.

UK College of Agriculture, Food and Environment

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