How to protect Landscape and Fruit Trees that are being killed by Ambrosia Beetles in the Tampa Bay Area

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By Mark Govan, Host “Florida Gardening” on 970WFLA Live on Sunday’s 7-9am

Tampa Bay’s Landscape and Fruit Trees are being killed by Ambrosia Beetles. Find out how to protect them

Trees throughout the Tampa Bay area are being eaten from the inside out by a small one-eighth inch long beetle called the Granulate Ambrosia Beetle. Do not let the size of these insects fool you, the damage they cause can be immense. The majority of these beetles attack trees, shrubs, and vines that have been weakened by environmental factors. These factors include trees that have been flooded or tipped over during this past hurricane season. Others could have been stressed by the recent drought we have been experiencing. Even parking your car under your favorite tree to keep cool can cause enough stress on the trees root system to weaken it, making the tree susceptible to these foraging beetles. Another beetle in the same family called the Redbay Ambrosia Beetle also targets trees. Unfortunately, the trees they go after are live healthy trees with no outward signs of stress. In this article, I will go over steps in identifying these insects and how you can lessen their impact in your landscape. Let’s get started.

Trees weakened by stress release pheromones insects are attracted to. Once an insect senses this pheromone, they make a beeline to it. When a female Granulate Ambrosia Beetle finds such a tree, she starts to gnaw a hole through the coarse bark and enters the tree. As she bores into the tree, the sawdust she creates is then pushed out of the entrance hole. As this sawdust exits the tree, it forms long toothpick sized straws, which can be as long as two inches. These straws break off the tree very easily as they are entirely formed of sawdust. Rain and high winds can also eliminate this sign of an infestation. You need several days of calm weather to see the straws. When you finally find a tree that is infested with these beetles, you will note that there are hundreds of these tiny straws emerging from the tree.

Remember, these Granulate Ambrosia beetles are merely secondary invaders and rarely attack healthy trees, shrubs, or plants. Once these pests have bored into the tree and cleaned the galleries of the sawdust, these beetles inoculate the sides of their tunnels with an ambrosia fungus. This fungus grows rapidly on the tunnels they have created turning them a reddish color. This fungus then becomes the primary food source of the ambrosia beetle and her young. Because these pests dig deep into the core of the tree, topical insecticide applications are ineffective. Tree injection services or systemic insecticides applied to the bark of the tree can help prevent an infestation before damage occurs to the tree. Systemic insecticides should not be applied to fruit-bearing trees.

Unfortunately, the Redbay Ambrosia beetles attack living trees in the Laurel family and trees with no outward signs of having any problems. Avocados, a member of this family, seem to be one of their preferred hosts. When the Redbay Ambrosia beetle finds a healthy host tree, it burrows into the tree just like its’ relative the Granulate beetle. Once the tunnels are formed they start inoculating the walls with the laurel wilt fungus they carry in a special pouch in their mouth. As this fungal pathogen grows on the tunnel walls, it spreads into the sapwood of the tree. You can see the spread of this disease in samples taken from cross-cut sections of the tree.

Purple stains in the sapwood indicate the spread of the fungus. At this stage, the trees circulatory system begins the spread of the fungus throughout the tree. Ultimately, the entire tree will die. Major limbs of the tree may die in as little as four weeks with large trees succumbing in eight weeks. There is no control for infested fruit-bearing trees. Homeowners should try to control the spread of this beetle through preventative measures of keeping the tree healthy, well fertilized, and watered frequently. Scouting your trees should be done weekly with contact insecticides applied to the bark of the tree to prevent foraging beetles from gaining a foothold. Knowledge of these pests and what to look for can be a great help in the ultimate control of these and other pests in the landscape. Maintaining a healthy landscape is paramount in any control program. Please enjoy your garden and remember, without plants, we would not be here.