Ambrosia beetles are common, tiny (only about 1/16” long), and can infest hundreds of different woody plant species. In South Carolina, these little beetles typically infest stressed trees, vines, or shrubs. Females will bore into stems and branches, creating a gallery. Beetles carry fungi on their bodies, and this fungus then grows inside the galleries, often appearing as white, gray, or black. The beetles feed on the fungus that grows inside the galleries.
Ambrosia beetle galleries. The white and black parts of the gallery indicate areas where fungi are growing.
David Coyle, ©2024, Clemson University
Most ambrosia beetles are secondary pests, meaning they only attack and impact plants that are already stressed (e.g., from frost damage, flooding, drought, or poor planting). For this reason, proper tree and plant care is essential to prevent ambrosia beetle damage. When ambrosia beetles attack, they often leave characteristic spaghetti-like projections coming out of the host. These projections are called noodles, frass tubes, or toothpicks and are made mostly of sawdust, beetle frass (poop), and some fungal mycelium. These are sure signs of ambrosia beetle infestation. In South Carolina, the granulate ambrosia beetle is one of the most common species that attack woody plants on landscapes.
Ambrosia beetle noodles. Each noodle represents a place where a single female ambrosia beetle entered the tree. These noodles are fragile and will blow off in the wind or get washed off by the rain. Two entrance holes are also visible in this picture in the middle of the stem, where adult females entered the stem; the noodle has just fallen off.
David Coyle, ©2024, Clemson University
Some species of ambrosia beetles are primary pests, meaning they can and do attack healthy trees. The redbay ambrosia beetle attacks all species in the family Lauraceae, which includes redbay, swampbay, avocado, and many others. This beetle carries the fungus that causes laurel wilt, which is a disease responsible for killing millions of trees across the Southeast. The black twig borer is common throughout the state but especially in the Lowcountry. This is one of the smallest ambrosia beetles and creates its galleries in small twigs. This damage causes branch flagging, which can reduce the aesthetics of trees and shrubs.
Branch flagging on a magnolia tree caused by the black twig borer.
David Coyle, ©2024, Clemson University
Managing ambrosia beetles is challenging since once they’re inside the tree, they are unaffected by insecticides (though several are available as topical or preventative treatments). In some cases, the damage can be pruned off. Overall, the best thing to do is to maintain the health of your trees, vines, and shrubs, which will prevent ambrosia beetle damage in the first place. This can be a challenge, as late or early freezes often stress plants, and this can lead to ambrosia beetle damage. But by maintaining the health of your woody plants, you’ll give them the best chance to fend off ambrosia beetle damage before it ever happens.
Black twig borer entrance hole. Pruning the affected branch just below this point can eliminate the beetle from the tree.
David Coyle, Clemson University
