Ambrosia Beetles

What Is An Ambrosia Beetle?

We've recently been made aware by the TN Dept of Agriculture that Ambrosia Beetles are once again at peak season. Some ambrosia beetles are native, performing a very important ecological role as de-composers by breaking down dying trees. Other Ambrosia Beetles are non-native (introduced from Asia and Europe in untreated packaging materials such as pallets) and can cause significant damage to your trees. For those of you who may not be aware of these pests, they can be very dangerous and cause significant damage attacking healthy fruit, nut or ornamental trees, often killing them by introducing fungi that block water movement. This can happen no matter the age of the tree or the health of the tree.

What types of plants do Ambrosia Beetles attack?

Although this isn't a all full list since Ambrosia beetles have an incredibly broad host range, attacking species including crape myrtles, redbuds, dogwoods, oaks, tulip poplars, figs, Japanese maples, flowering cherries, sweetgum, magnolia, rhododendron, azalea, pecan, peach, apple, plum, and persimmon. Given that this list isn't all inclusive since we find out additional information on these beetles each year, it is best to keep a close look out on all of your trees while in peak season. Keep in mind that they require wood with internal moisture content of at least 48%. So, while they may attack dying or recently dead trees, they will not attack completely dead trees or dry firewood.

How Will I know If Have Ambrosia Beetles?

These beetles are tiny and you probably won't see them but rather the bore into the trees that they have chosen. They don't actually consume the wood of the tree instead, they dig tunnels specifically to create a environment suitable for the growth of the ambrosia fungi. The fungus actually kills the plant by clogging the stem so no water can move up from the roots. So you see, they don't eat the plant but rather they gnaw the plant and push it out behind them as they construct their tunnels. The most recognizable sign is the presence of sawdust plugs, also known as “toothpicks,” that stick out from the bark, each representing an entry point of a single female beetle. You will see signs like below to identify the infestation:

How Do I Help Eliminate An Infestation?

Managing an existing infestation is difficult because the beetles are protected inside the tree and do not consume the wood, making systemic insecticides (soil based) largely ineffective. The most effective way to prevent damage is through proper tree care, as healthy trees are less attractive to beetles and can better withstand low level infestations. Prevention starts at planting – property owners should select trees suited for our USDA hardiness zone and site them appropriately. Irrigate as needed during extended periods of drought, and avoid wounding trees with maintenance equipment. These wounds put further stress on trees and could serve as entry points for the ambrosia beetles. Weird but the beetles actually smell chemicals released by sick trees.

Even with the best protection though, healthy trees naturally may still be attacked by ambrosia beetles. Once beetles have attacked a tree, early detection and removal of infested plant materials is the best solution. While topical treatments, such as permethrin or bifenthrin (we carry several types at the garden center), can repel females, the timing of application must be very precise (as a preventative). If a tree is infested, removing the affected material is the best solution. For vigorously growing plants, like figs, only the damaged trunks need to be removed, as they can regrow from the stump. Importantly, infested wood does not need to be burned. The beetles are already well-established in the ecosystem, and burning will not significantly reduce their populations. Infested wood can be composted, chipped, or left to dry. 

How Long Will This Last?

These beetles normally start wood boring activity as soon as we get three 70 degrees days in a row. That's traditionally in the early spring March & April here in Tennessee. Boring activity lasts until the trees fully leaf out in mid-April. 

Feel free to discuss any additional questions that you may have with us at the garden center. For more information, you can visit https://www.tn.gov/protecttnforests/insects/granulated-ambrosia-beetle.html